SqExpress

The library provides a generic sql syntax tree with export to MS t-SQL, PostgreSQL and MySQL text.

It also provides a set of builders and operators which will help you building complex Sql expressions.

It does not use LINQ and your C# code will be close to real SQL as much as possible, so it can be used when you need the full SQL flexibility to create efficient Db requests.

It is delivered with a simple but efficient data access mechanism which warps ADO.Net DbConnection and can be used with MS SQL Client or Npgsql or MySQL Connector.

It can be used in conjunction with the “Code First” concept when you declare SQL tables as C# classes with possibility to generate recreation scripts for a target platform (MS SQL or PostgreSQL or MySQL)

It can be used in conjunction with the “Database First” concept using an included code modification utility. The utility is also can be used to generate flexible DTO classes with all required database mappings.

Articles

"Syntax Tree and Alternative to LINQ in Interaction with SQL Databases" - explains the library principles;
"Filtering by Dynamic Attributes" - shows how to create dynamic queries using the library.

Demo Application

You can find a realistic usage of the library in this ASP.Net demo application - SqGoods

Content

Get Started

Get Started

Add a reference to the library package on Nuget.org:

Install-Package SqExpress

and start with "Hello World":

static void Main()
{
    var query = SqQueryBuilder.Select("Hello World!").Done();

    Console.WriteLine(TSqlExporter.Default.ToSql(query));
}

Now let's get rid of the necessity in writing "SqQueryBuilder.":

using static SqExpress.SqQueryBuilder;
...
    var query = Select("Hello World!").Done();

    Console.WriteLine(TSqlExporter.Default.ToSql(query));

The result will be:

SELECT 'Hello World!'

(Re)Creating Table

Ok, let's try to select some data from a real table, but first we need to describe the table:

Note: Such classes can be auto-generated (updated) using information from an existing database. See "Table Descriptors Scaffolding"

public class TableUser : TableBase
{
    public readonly Int32TableColumn UserId;
    public readonly StringTableColumn FirstName;
    public readonly StringTableColumn LastName;
    //Audit Columns
    public readonly Int32TableColumn Version;
    public readonly DateTimeTableColumn ModifiedAt;

    public TableUser(): this(default){}

    public TableUser(Alias alias) : base("dbo", "User", alias)
    {
        this.UserId = this.CreateInt32Column("UserId", 
            ColumnMeta.PrimaryKey().Identity());

        this.FirstName = this.CreateStringColumn("FirstName", 
            size: 255, isUnicode: true);

        this.LastName = this.CreateStringColumn("LastName", 
            size: 255, isUnicode: true);

        this.Version = this.CreateInt32Column("Version",
            ColumnMeta.DefaultValue(0));

        this.ModifiedAt = this.CreateDateTimeColumn("ModifiedAt",
            columnMeta: ColumnMeta.DefaultValue(SqQueryBuilder.GetUtcDate()));

        //Indexes
        this.AddIndex(this.FirstName);
        this.AddIndex(this.LastName);
    }
}

and if the table does not exist let's create it:

static async Task Main()
{
    using var connection = new SqlConnection("connection_string");
    {
        using (var database = new SqDatabase<SqlConnection>(
            connection: connection,
            commandFactory: (conn, sql) 
                => new SqlCommand(cmdText: sql, connection: conn),
            sqlExporter: TSqlExporter.Default))
        {
            var tUser = new TableUser();

            await database.Statement(tUser.Script.DropAndCreate());
        }
    }
}

Note: See PostgreSQL or MySQL sections if you need to work with these databases.

Actual T-SQL:

IF EXISTS
(
    SELECT TOP 1 1 
    FROM [INFORMATION_SCHEMA].[TABLES] 
    WHERE [TABLE_SCHEMA]='dbo' AND [TABLE_NAME]='User'
) 
    DROP TABLE [dbo].[User];

CREATE TABLE [dbo].[User]
(
    [UserId] int NOT NULL  IDENTITY (1, 1),
    [FirstName] [nvarchar](255) NOT NULL,
    [LastName] [nvarchar](255) NOT NULL,
    [Version] int NOT NULL,
    [ModifiedAt] datetime NOT NULL,
    CONSTRAINT [PK_dbo_User] PRIMARY KEY ([UserId])
);

Inserting Data

Now it is the time to insert some date in the table:

...
var data = new[]
{
    new {FirstName = "Francois", LastName = "Sturman"},
    new {FirstName = "Allina", LastName = "Freeborne"},
    new {FirstName = "Maye", LastName = "Maloy"},
};

await InsertDataInto(tUser, data)
    .MapData(s => s
        .Set(s.Target.FirstName, s.Source.FirstName)
        .Set(s.Target.LastName, s.Source.LastName))
    .AlsoInsert(s => s
        .Set(s.Target.Version, 1)
        .Set(s.Target.ModifiedAt, GetUtcDate()))
    .Exec(database);
...

Actual T-SQL:

INSERT INTO [dbo].[User]([FirstName],[LastName],[Version],[ModifiedAt]) 
SELECT [FirstName],[LastName],1,GETUTCDATE() 
FROM 
(VALUES 
    ('Francois','Sturman'),
    ('Allina','Freeborne')
    ,('Maye','Maloy')
)[A0]([FirstName],[LastName])

Selecting data

and select it:

var selectResult = await Select(tUser.UserId, tUser.FirstName, tUser.LastName)
    .From(tUser)
    .OrderBy(tUser.FirstName, tUser.LastName)
    .QueryList(database,
        r => (
            Id: tUser.UserId.Read(r),
            FirstName: tUser.FirstName.Read(r),
            LastName: tUser.LastName.Read(r)));
foreach (var record in selectResult)
{
    Console.WriteLine(record);
}

Actual T-SQL:

SELECT [A0].[UserId],[A0].[FirstName],[A0].[LastName] 
FROM [dbo].[User] [A0] 
ORDER BY [A0].[FirstName],[A0].[LastName]

Result:

(2, Allina, Freeborne)
(1, Francois, Sturman)
(3, Maye, Maloy)

Updating data

Now let's fix the typo:

await Update(tUser)
    .Set(tUser.LastName, "Malloy")
    .Set(tUser.Version, tUser.Version+1)
    .Set(tUser.ModifiedAt, GetUtcDate())
    .Where(tUser.LastName == "Maloy")
    .Exec(database);

//Writing to console without storing data in memory
await Select(tUser.Columns)
    .From(tUser)
    .Query(database, record=>
    {
        Console.Write(tUser.UserId.Read(record) + ",");
        Console.Write(tUser.FirstName.Read(record) + " ");
        Console.Write(tUser.LastName.Read(record) + ",");
        Console.Write(tUser.Version.Read(record) + ",");
        Console.WriteLine(tUser.ModifiedAt.Read(record).ToString("s"));
        return agg;
    });

Actual T-SQL:

UPDATE [A0] SET 
    [A0].[LastName]='Malloy',
    [A0].[Version]=[A0].[Version]+1,
    [A0].[ModifiedAt]=GETUTCDATE() 
FROM [dbo].[User] [A0] 
WHERE [A0].[LastName]='Maloy'```

Result:

1,Francois Sturman,1,2020-10-12T11:32:16
2,Allina Freeborne,1,2020-10-12T11:32:16
3,Maye Malloy,2,2020-10-12T11:32:17

Note: In addition to Update the library also has Insert and IdentityInsert helpers (see Database Data Export/Import to find an example)

Deleting data

Unfortunately, regardless the fact the typo is fixed, we have to say "Good Bye" to May*:

await Delete(tUser)
    .Where(tUser.FirstName.Like("May%"))
    .Output(tUser.UserId)
    .Query(database, (record)=>
    {
        Console.WriteLine("Removed user id: " + tUser.UserId.Read(record));
    });

Actual T-SQL:

DELETE [A0] 
OUTPUT DELETED.[UserId] 
FROM [dbo].[User] [A0] 
WHERE [A0].[FirstName] LIKE 'May%'

Result:

Removed user id: 3

More Tables and foreign keys

To crete more complex queries we need more than one table. Let's add a couple more:

dbo.Company

public class TableCompany : TableBase
{
    public readonly Int32TableColumn CompanyId;
    public readonly StringTableColumn CompanyName;

    //Audit Columns
    public readonly Int32TableColumn Version;
    public readonly DateTimeTableColumn ModifiedAt;

    public TableCompany() : this(default) { }

    public TableCompany(Alias alias) : base("dbo", "Company", alias)
    {
        this.CompanyId = this.CreateInt32Column(
            nameof(this.CompanyId), ColumnMeta.PrimaryKey().Identity());

        this.CompanyName = this.CreateStringColumn(
            nameof(this.CompanyName), 250);

        this.Version = this.CreateInt32Column("Version",
            ColumnMeta.DefaultValue(0));

        this.ModifiedAt = this.CreateDateTimeColumn("ModifiedAt",
            columnMeta: ColumnMeta.DefaultValue(SqQueryBuilder.GetUtcDate()));
    }
}

dbo.Customer

public class TableCustomer : TableBase
{
    public Int32TableColumn CustomerId { get; }
    public NullableInt32TableColumn UserId { get; }
    public NullableInt32TableColumn CompanyId { get; }

    public TableCustomer() : this(default) { }

    public TableCustomer(Alias alias) : base("dbo", "Customer", alias)
    {
        this.CustomerId = this.CreateInt32Column(
            nameof(this.CustomerId), ColumnMeta.PrimaryKey().Identity());

        this.UserId = this.CreateNullableInt32Column(
            nameof(this.UserId), 
            ColumnMeta.ForeignKey<TableUser>(u => u.UserId));

        this.CompanyId = this.CreateNullableInt32Column(
            nameof(this.CompanyId), 
            ColumnMeta.ForeignKey<TableCompany>(u => u.CompanyId));

        //Indexes            
        this.AddUniqueIndex(this.UserId, this.CompanyId);
        this.AddUniqueIndex(this.CompanyId, this.UserId);
    }
}

Pay attention to the way how the foreign keys are defined:

ColumnMeta.ForeignKey<TableUser>(u => u.UserId)

And indexes:

this.AddUniqueIndex(this.UserId, this.CompanyId);
this.AddUniqueIndex(this.CompanyId, this.UserId);

Since now we have the foreign keys we have to delete and create the table in the specific order:

var tables = new TableBase[]{ new TableUser() , new TableCompany(), new TableCustomer() };

foreach (var table in tables.Reverse())
{
    await database.Statement(table.Script.DropIfExist());
}
foreach (var table in tables)
{
    await database.Statement(table.Script.Create());
}

Now we can insert some companies:

var tCompany = new TableCompany();

Console.WriteLine("Companies:");

await InsertDataInto(tCompany, new[] {"Microsoft", "Google"})
    .MapData(s => s.Set(s.Target.CompanyName, s.Source))
    .AlsoInsert(s => s
        .Set(s.Target.Version, 1)
        .Set(s.Target.ModifiedAt, GetUtcDate()))
    .Output(tCompany.CompanyId, tCompany.CompanyName)
    .Query(database, (r) =>
    {
        Console.WriteLine($"Id: {tCompany.CompanyId.Read(r)}, Name: {tCompany.CompanyName.Read(r)}");
    });

and create "Customers":

var tUser = new TableUser();
var tCompany = new TableCompany();
var tCustomer = new TableCustomer();
var tSubCustomer = new TableCustomer();

//Users
await InsertInto(tCustomer, tCustomer.UserId)
    .From(
        Select(tUser.UserId)
            .From(tUser)
            .Where(!Exists(
                SelectOne()
                    .From(tSubCustomer)
                    .Where(tSubCustomer.UserId == tUser.UserId))))
    .Exec(database);

//Companies
await InsertInto(tCustomer, tCustomer.CompanyId)
    .From(
        Select(tCompany.CompanyId)
            .From(tCompany)
            .Where(!Exists(
                SelectOne()
                    .From(tSubCustomer)
                    .Where(tSubCustomer.CompanyId == tCompany.CompanyId))))
    .Exec(database);

Actual T-SQL:

INSERT INTO [dbo].[Customer]([UserId]) 
SELECT [A0].[UserId] 
FROM [dbo].[User] [A0] WHERE NOT EXISTS
(
    SELECT 1 
    FROM [dbo].[Customer] [A1] 
    WHERE [A1].[UserId]=[A0].[UserId]
)

INSERT INTO [dbo].[Customer]([CompanyId]) 
SELECT [A0].[CompanyId] 
FROM [dbo].[Company] [A0] 
WHERE NOT EXISTS(
    SELECT 1 FROM [dbo].[Customer] [A1] 
    WHERE [A1].[CompanyId]=[A0].[CompanyId]
)

Data Selection

Joining Tables

Now we can Join all the tables:

var tUser = new TableUser();
var tCompany = new TableCompany();
var tCustomer = new TableCustomer();

var cType = CustomColumnFactory.Int16("Type");
var cName = CustomColumnFactory.String("Name");

var customers = await Select(
        tCustomer.CustomerId,
        Case()
            .When(IsNotNull(tUser.UserId))
            .Then(Cast(Literal(1), SqlType.Int16))
            .When(IsNotNull(tCompany.CompanyId))
            .Then(Cast(Literal(2), SqlType.Int16))
            .Else(Null)
            .As(cType),
        Case()
            .When(IsNotNull(tUser.UserId))
            .Then(tUser.FirstName + " " + tUser.LastName)
            .When(IsNotNull(tCompany.CompanyId))
            .Then(tCompany.CompanyName)
            .Else(Null)
            .As(cName)
    )
    .From(tCustomer)
    .LeftJoin(tUser, on: tUser.UserId == tCustomer.UserId)
    .LeftJoin(tCompany, on: tCompany.CompanyId == tCustomer.CompanyId)
    .QueryList(database,
        r => (Id: tCustomer.CustomerId.Read(r), CustomerType: cType.Read(r), Name: cName.Read(r)));

foreach (var customer in customers)
{
    Console.WriteLine($"Id: {customer.Id}, Name: {customer.Name}, Type: {customer.CustomerType}");
}

Actual T-SQL:

SELECT 
    [A0].[CustomerId],
    CASE 
        WHEN [A1].[UserId] IS NOT NULL 
        THEN CAST(1 AS smallint) 
        WHEN [A2].[CompanyId] IS NOT NULL 
        THEN CAST(2 AS smallint) 
        ELSE NULL END 
    [Type],
    CASE 
        WHEN [A1].[UserId] IS NOT NULL 
        THEN [A1].[FirstName]+' '+[A1].[LastName] 
        WHEN [A2].[CompanyId] IS NOT NULL 
        THEN [A2].[CompanyName] 
        ELSE NULL END 
    [Name] 
FROM [dbo].[Customer] [A0] 
LEFT JOIN [dbo].[User] [A1] 
    ON [A1].[UserId]=[A0].[UserId] 
LEFT JOIN [dbo].[Company] [A2] 
    ON [A2].[CompanyId]=[A0].[CompanyId]

Result:

Id: 1, Name: Francois Sturman, Type: 1
Id: 2, Name: Allina Freeborne, Type: 1
Id: 3, Name: Microsoft, Type: 2
Id: 4, Name: Google, Type: 2

Aliasing

Every time you create a table object, it is associated by default with an alias that will be used wherever you refer to the table. Each new instance will use a new alias. However you can explicitly specify your own alias or omit it:

var tUser = new User("USR");
var tUserNoAlias = new User(Alias.Empty);

Select(tUser.UserId).From(tUser);
Select(tUserNoAlias.UserId).From(tUserNoAlias);

Actual T-SQL:

--var tUser = new User("USR");
SELECT [USR].[UserId] FROM [dbo].[user] [USR]

--var tUserNoAlias = new User(Alias.Empty);
SELECT [UserId] FROM [dbo].[user]

Derived Tables

The previous query is quite complex so it makes sense to store it as a derived table and reuse it in future:

public class DerivedTableCustomer : DerivedTableBase
{
    public readonly Int32CustomColumn CustomerId;

    public readonly Int16CustomColumn Type;

    public readonly StringCustomColumn Name;

    public DerivedTableCustomer(Alias alias = default) : base(alias)
    {
        this.CustomerId = this.CreateInt32Column("CustomerId");
        this.Type = this.CreateInt16Column("Type");
        this.Name = this.CreateStringColumn("Name");
    }

    protected override IExprSubQuery CreateQuery()
    {
        var tUser = new TableUser();
        var tCompany = new TableCompany();
        var tCustomer = new TableCustomer();

        return Select(
                tCustomer.CustomerId.As(this.CustomerId),
                Case()
                    .When(IsNotNull(tUser.UserId))
                    .Then(Cast(Literal(1), SqlType.Int16))
                    .When(IsNotNull(tCompany.CompanyId))
                    .Then(Cast(Literal(2), SqlType.Int16))
                    .Else(Null)
                    .As(this.Type),
                Case()
                    .When(IsNotNull(tUser.UserId))
                    .Then(tUser.FirstName + " " + tUser.LastName)
                    .When(IsNotNull(tCompany.CompanyId))
                    .Then(tCompany.CompanyName)
                    .Else(Null)
                    .As(this.Name)
            )
            .From(tCustomer)
            .LeftJoin(tUser, on: tUser.UserId == tCustomer.UserId)
            .LeftJoin(tCompany, on: tCompany.CompanyId == tCustomer.CompanyId)
            .Done();
    }
}

and this is how it can be reused:

var tCustomer = new DerivedTableCustomer("CUST");

var customers = await Select(tCustomer.Columns)
    .From(tCustomer)
    .Where(tCustomer.Type == 2 | tCustomer.Name.Like("%Free%"))
    .OrderBy(Desc(tCustomer.Name))
    .OffsetFetch(1, 2)
    .QueryList(database,
        r => (Id: tCustomer.CustomerId.Read(r), CustomerType: tCustomer.Type.Read(r), Name: tCustomer.Name.Read(r)));

foreach (var customer in customers)
{
    Console.WriteLine($"Id: {customer.Id}, Name: {customer.Name}, Type: {customer.CustomerType}");
}

Actual T-SQL:

SELECT 
    [CUST].[CustomerId],
    [CUST].[Type],
    [CUST].[Name] 
FROM 
(
    SELECT 
        [A0].[CustomerId] [CustomerId],
        CASE 
        WHEN [A1].[UserId] IS NOT NULL 
        THEN CAST(1 AS smallint) 
        WHEN [A2].[CompanyId] IS NOT NULL 
        THEN CAST(2 AS smallint) 
        ELSE NULL 
        END [Type],
        CASE 
        WHEN [A1].[UserId] IS NOT NULL 
        THEN [A1].[FirstName]+' '+[A1].[LastName] 
        WHEN [A2].[CompanyId] IS NOT NULL 
        THEN [A2].[CompanyName] 
        ELSE NULL END [Name] 
    FROM [dbo].[Customer] [A0] 
    LEFT JOIN [dbo].[User] [A1] 
        ON [A1].[UserId]=[A0].[UserId] 
    LEFT JOIN [dbo].[Company] [A2] 
        ON [A2].[CompanyId]=[A0].[CompanyId]
)[CUST] 
WHERE 
    [CUST].[Type]=2 OR [CUST].[Name] LIKE '%Free%' 
ORDER BY [CUST].[Name] DESC 
OFFSET 1 ROW FETCH NEXT 2 ROW ONLY

Result:

Id: 4, Name: Google, Type: 2
Id: 2, Name: Allina Freeborne, Type: 1

Subquries

It is not necessary to create a new class when you need a subquery - it can be directly described in an original expression. It is enough just to predefine the aliases for columns and tables:

var num = CustomColumnFactory.Int32("3");
//Note: "3" (the first value) is for compatibility with MySql
//which does not properly support values constructors

var sum = CustomColumnFactory.Int32("Sum");

var numbers = Values(3, 1, 1, 7, 3, 7, 3, 7, 7, 8).AsColumns(num);
var numbersSubQuery = TableAlias();

var mostFrequentNum = (int) await
    SelectTop(1, numbersSubQuery.Column(num))
        .From(
            Select(numbers.Column(num), CountOne().As(sum))
                .From(numbers)
                .GroupBy(numbers.Column(num))
                .As(numbersSubQuery)
        )
        .OrderBy(Desc(numbersSubQuery.Column(sum)))
        .QueryScalar(database);

Console.WriteLine("The most frequent number: "  + mostFrequentNum);

Actual T-SQL:

SELECT 
    TOP 1 [A0].[3] 
FROM 
(
    SELECT [A1].[3],COUNT(1) [Sum] 
    FROM (VALUES (3),(1),(1),(7),(3),(7),(3),(7),(7),(8))[A1]([3]) 
    GROUP BY [A1].[3]
) [A0] 
ORDER BY [A0].[Sum] DESC

Note: In this example you can see how to use Table Value Constructor

CTE

To perform recursive (actually "incremental") requests the library supports CTE (Common Table Expressions).

The typical scenario is traversing some hierarchical data stored in a table, for example the following query will return a tree closure table:

class CteTreeClosure : CteBase
{
    public CteTreeClosure(Alias alias = default) : base(nameof(CteTreeClosure), alias)
    {
        this.Id = this.CreateInt32Column(nameof(this.Id));
        this.ParentId = this.CreateNullableInt32Column(nameof(this.ParentId));
        this.Depth = this.CreateInt32Column(nameof(this.Depth));
    }

    public Int32CustomColumn Id { get; }

    public NullableInt32CustomColumn ParentId { get; }

    public Int32CustomColumn Depth { get; }

    public override IExprSubQuery CreateQuery()
    {
        var initial = new TreeData();
        var current = new TreeData();

        var previous = new CteTreeClosure();

        return Select(initial.Id, initial.ParentId, Literal(1).As(this.Depth))
            .From(initial)
            .UnionAll(Select(
                    previous.Id,
                    current.ParentId,
                    (previous.Depth + 1).As(this.Depth))
                .From(current)
                .InnerJoin(previous, on: previous.ParentId == current.Id))
            .Done();
    }
}
...

var result = await Select(treeClosure.Id, treeClosure.ParentId, treeClosure.Depth)
    .From(treeClosure)
    .QueryList(context.Database,
        r => (
            Id: treeClosure.Id.Read(r),
            ParentId: treeClosure.ParentId.Read(r),
            Depth: treeClosure.Depth.Read(r)));

Working with CTEs in SqExpress is very similar to derived tables - you need to create a class derived from CteBase abstract class, describe columns and implement CreateQuery method which will return actual CTE query where the class can be used as a table descriptor (to create recursion if it is required).

The example code will generate the following sql:

WITH [CteTreeClosure] AS(
        SELECT [A1].[Id],[A1].[ParentId],1 [Depth] 
        FROM [#TreeData] [A1] 
    UNION ALL 
        SELECT [A2].[Id],[A3].[ParentId],[A2].[Depth]+1 [Depth] 
        FROM [#TreeData] [A3] 
        JOIN [CteTreeClosure] [A2] 
            ON [A2].[ParentId]=[A3].[Id]
)
                
SELECT [A0].[Id],[A0].[ParentId],[A0].[Depth] FROM [CteTreeClosure] [A0]

MySql

WITH RECURSIVE `CteTreeClosure` AS(
        SELECT `A0`.`Id`,`A0`.`ParentId`,1 `Depth` 
        FROM `TreeData` `A0` 
    UNION ALL 
        SELECT `A1`.`Id`,`A2`.`ParentId`,`A1`.`Depth`+1 `Depth` 
        FROM `TreeData` `A2` 
        JOIN `CteTreeClosure` `A1` 
            ON `A1`.`ParentId`=`A2`.`Id`
) 

SELECT `A3`.`Id`,`A3`.`ParentId`,`A3`.`Depth` FROM `CteTreeClosure` `A3````

Analytic And Window Functions

SqExpress supports common analytic and window functions like ROW_NUMBER, RANK, FIRST_VALUE, LAST_VALUE etc.

var cUserName = CustomColumnFactory.String("Name");
var cNum = CustomColumnFactory.Int64("Num");
var cFirst = CustomColumnFactory.String("First");
var cLast = CustomColumnFactory.String("Last");

var user = new TableUser();

await Select(
        (user.FirstName + " " + user.LastName)
        .As(cUserName),
        RowNumber()
            /*.OverPartitionBy(some fields)*/
            .OverOrderBy(user.FirstName)
            .As(cNum),
        FirstValue(user.FirstName + " " + user.LastName)
            /*.OverPartitionBy(some fields)*/
            .OverOrderBy(user.FirstName)
            .FrameClauseEmpty()
            .As(cFirst),
        LastValue(user.FirstName + " " + user.LastName)
            /*.OverPartitionBy(some fields)*/
            .OverOrderBy(user.FirstName)
            .FrameClause(
                FrameBorder.UnboundedPreceding,
                FrameBorder.UnboundedFollowing)
            .As(cLast))
    .From(user)
    .Query(database,
        r => Console.WriteLine(
            $"Num: {cNum.Read(r)}, Name: {cUserName.Read(r)}, " +
            $"First: {cFirst.Read(r)}, Last: {cLast.Read(r)}"));

Actual T-SQL:

SELECT 
    [A0].[FirstName]+' '+[A0].[LastName] 
        [Name],
    ROW_NUMBER()OVER(ORDER BY [A0].[FirstName]) 
        [Num],
    FIRST_VALUE([A0].[FirstName]+' '+[A0].[LastName])
        OVER(ORDER BY [A0].[FirstName]) 
        [First],
    LAST_VALUE([A0].[FirstName]+' '+[A0].[LastName])
        OVER(ORDER BY [A0].[FirstName] 
            ROWS BETWEEN 
            UNBOUNDED PRECEDING 
            AND UNBOUNDED FOLLOWING) 
        [Last] 
FROM [dbo].[User] [A0]

Set Operators

The library supports all the SET operators:

//If you need to repeat one query several times 
// you can store it in a variable
var select1 = Select(1);
var select2 = Select(2);

var result = await select1
    .Union(select2)
    .UnionAll(select2)
    .Except(select2)
    .Intersect(select1.Union(select2))
    .QueryList(database, r => r.GetInt32(0));

Console.WriteLine("Result Of Set Operators:");
Console.WriteLine(result[0]);

Ans actual SQL will be:

(
    (
        (
            SELECT 1 
            UNION 
            SELECT 2
        ) 
        UNION ALL 
        SELECT 2
    ) 
    EXCEPT 
    SELECT 2
) 
INTERSECT 
(
    SELECT 1 
    UNION 
    SELECT 2
)

Merge

As a bonus, if you use MS SQL Server, you can use Merge statement:

var data = new[]
{
    new {FirstName = "Francois", LastName = "Sturman2"},
    new {FirstName = "Allina", LastName = "Freeborne2"},
    new {FirstName = "Maye", LastName = "Malloy"},
};

var action = CustomColumnFactory.String("Actions");
var inserted = CustomColumnFactory.NullableInt32("Inserted");
var deleted = CustomColumnFactory.NullableInt32("Deleted");

var tableUser = new TableUser();
await MergeDataInto(tableUser, data)
    .MapDataKeys(s => s
        .Set(s.Target.FirstName, s.Source.FirstName))
    .MapData(s => s
        .Set(s.Target.LastName, s.Source.LastName))
    .WhenMatchedThenUpdate()
    .AlsoSet(s => s
        .Set(s.Target.Version, s.Target.Version + 1)
        .Set(s.Target.ModifiedAt, GetUtcDate()))
    .WhenNotMatchedByTargetThenInsert()
    .AlsoInsert(s => s
        .Set(s.Target.Version, 1)
        .Set(s.Target.ModifiedAt, GetUtcDate()))
    .Output((t, s, m) => m.Inserted(t.UserId.As(inserted)).Deleted(t.UserId.As(deleted)).Action(action))
    .Done()
    .Query(database,
        (r) =>
        {
            Console.WriteLine($"UserId Inserted: {inserted.Read(r)},UserId Deleted: {deleted.Read(r)} , Action: {action.Read(r)}");
        });

Actual T-SQL:

MERGE [dbo].[User] [A0] 
USING (
    VALUES 
    ('Francois','Sturman2'),
    ('Allina','Freeborne2'),
    ('Maye','Malloy'))[A1]([FirstName],[LastName]) 
ON [A0].[FirstName]=[A1].[FirstName] 
WHEN MATCHED 
THEN UPDATE SET [A0].[LastName]=[A1].[LastName],[A0].[Version]=[A0].[Version]+1,[A0].[ModifiedAt]=GETUTCDATE() 
WHEN NOT MATCHED 
THEN INSERT([FirstName],[LastName],[Version],[ModifiedAt]) 
VALUES([A1].[FirstName],[A1].[LastName],1,GETUTCDATE()) 
OUTPUT INSERTED.[UserId] [Inserted],DELETED.[UserId] [Deleted],$ACTION [Actions];

Result:

UserId Inserted: 4,UserId Deleted:  , Action: INSERT
UserId Inserted: 1,UserId Deleted: 1 , Action: UPDATE
UserId Inserted: 2,UserId Deleted: 2 , Action: UPDATE

For PostgresSQL or MySQL the library generates polyfills that use a temporary table to store passed data. For example the previous query will be converted into the following statements (OUTPUT is not supported):

Actual MYSQL:

CREATE TEMPORARY TABLE `tmpMergeDataSource`(
    `FirstName` varchar(8) character set utf8,
    `LastName` varchar(10) character set utf8,
    CONSTRAINT PRIMARY KEY (`FirstName`))
;
INSERT INTO `tmpMergeDataSource`(`FirstName`,`LastName`) 
VALUES ('Francois','Sturman2'),('Allina','Freeborne2'),('Maye','Malloy')
;
UPDATE `User` `A0`,`tmpMergeDataSource` `A1` 
SET 
    `A0`.`LastName`=`A1`.`LastName`,
    `A0`.`Version`=`A0`.`Version`+1,
    `A0`.`ModifiedAt`=UTC_TIMESTAMP()
WHERE `A0`.`FirstName`=`A1`.`FirstName`
;
INSERT INTO `User`(`FirstName`,`LastName`,`Version`,`ModifiedAt`) 
SELECT `A1`.`FirstName`,`A1`.`LastName`,1,UTC_TIMESTAMP() 
FROM `tmpMergeDataSource` `A1` 
WHERE NOT EXISTS(SELECT 1 FROM `User` `A0` WHERE `A0`.`FirstName`=`A1`.`FirstName`)
;
DROP TABLE `tmpMergeDataSource`;

Temporary Tables

In some scenarios temporary tables might be very useful and you can create such table as follows:

public class TempTable : TempTableBase
{
    public TempTable(Alias alias = default) : base("tempTable", alias)
    {
        this.Id = CreateInt32Column(nameof(Id),
            ColumnMeta.PrimaryKey().Identity());

        this.Name = CreateStringColumn(nameof(Name), 255);
    }

    public readonly Int32TableColumn Id;

    public readonly StringTableColumn Name;
}

and then use it:

var tmp = new TempTable();

var tableUser = new TableUser();
var tableCompany = new TableCompany();

await database.Statement(tmp.Script.Create());

//Users
await InsertInto(tmp, tmp.Name)
    .From(Select(tableUser.FirstName + " "+ tableUser.LastName)
    .From(tableUser))
    .Exec(database);

//Companies
await InsertInto(tmp, tmp.Name)
    .From(Select(tableCompany.CompanyName)
    .From(tableCompany))
    .Exec(database);

await Select(tmp.Columns)
    .From(tmp)
    .OrderBy(tmp.Name)
    .Query(database,
        (r) =>
        {
            Console.WriteLine($"Id: {tmp.Id.Read(r)}, Name: {tmp.Name.Read(r)}");
        });

//Dropping the temp table is optional
//It will be automatically removed when
//the connection is closed
await database.Statement(tmp.Script.Drop());

The result will be:

Id: 2, Name: Allina Freeborne
Id: 1, Name: Francois Sturman
Id: 4, Name: Google
Id: 3, Name: Microsoft

Database Data Export Import

Having a list of table descriptors you can easily export all theirs data into any text format - JSON for example:

static async Task<string> ToJsonString(ISqDatabase database, TableBase[] tableBases)
{
    using var ms = new MemoryStream();
    using Utf8JsonWriter writer = new Utf8JsonWriter(ms);

    writer.WriteStartObject();
    foreach (var table in tableBases)
    {
        await ReadTableDataIntoJson(writer, database, table);
    }

    writer.WriteEndObject();
    writer.Flush();

    var s = Encoding.UTF8.GetString(ms.ToArray());
    return s;
}

static async Task ReadTableDataIntoJson(Utf8JsonWriter writer, ISqDatabase database, TableBase table)
{
    writer.WriteStartArray(table.FullName.AsExprTableFullName().TableName.Name);

    writer.WriteStartArray();
    foreach (var column in table.Columns)
    {
        writer.WriteStringValue(column.ColumnName.Name);
    }

    writer.WriteEndArray();

    await Select(table.Columns)
        .From(table)
        .Query(database,
            r =>
            {
                writer.WriteStartArray();
                foreach (var column in table.Columns)
                {
                    var readAsString = column.ReadAsString(r);
                    writer.WriteStringValue(readAsString);
                }

                writer.WriteEndArray();
            });

    writer.WriteEndArray();
}

Result:

{
    "User": [
	["UserId", "FirstName", "LastName", "Version", "ModifiedAt"], 
	["1", "Francois", "Sturman2", "2", "2021-10-26T08:07:03.160"], 
	["2", "Allina", "Freeborne2", "2", "2021-10-26T08:07:03.160"], 
	["4", "Maye", "Malloy", "1", "2021-10-26T08:07:03.160"]],
    "Company": [
	["CompanyId", "CompanyName", "Version", "ModifiedAt"], 
	["1", "Microsoft", "1", "2021-10-26T08:07:03.080"], 
	["2", "Google", "1", "2021-10-26T08:07:03.080"]],
    "Customer": [
	["CustomerId", "UserId", "CompanyId"], 
	["3", null, "1"], 
	["4", null, "2"], 
	["1", "1", null], 
	["2", "2", null]]
}

Import from a text format is not difficult as well:

static async Task InsertTableData(ISqDatabase database, TableBase table, JsonElement element)
{
    var columnsDict = table.Columns.ToDictionary(i => i.ColumnName.Name, i => i);
    var colIndexes = element.EnumerateArray().First().EnumerateArray().Select(c => c.GetString()).ToList();

    var rowsEnumerable = element
        .EnumerateArray()
        .Skip(1)
        .Select(e =>
            e.EnumerateArray()
                .Select((c, i) =>
                    columnsDict[colIndexes[i]]
                        .FromString(c.ValueKind == JsonValueKind.Null ? null : c.GetString()))
                .ToList());

    var insertExpr = IdentityInsertInto(table, table.Columns).Values(rowsEnumerable);
    if (!insertExpr.Insert.Source.IsEmpty)
    {
        await insertExpr.Exec(database);
    }
}

Syntax Tree

You can go through an existing syntax tree object and modify if it is required:

//Var some external filter..
ExprBoolean filter = CustomColumnFactory.Int16("Type") == 2 /*Company*/;

var tableCustomer = new TableCustomer();

var baseSelect = Select(tableCustomer.CustomerId)
    .From(tableCustomer)
    .Where(filter)
    .Done();

//Checking that filter has "Type" column
var hasVirtualColumn = filter.SyntaxTree()
    .FirstOrDefault<ExprColumnName>(e => e.Name == "Type") != null;

if (hasVirtualColumn)
{
    baseSelect = (ExprQuerySpecification) baseSelect.SyntaxTree()
        .Modify(e =>
        {
            var result = e;
            //Joining with the sub query
            if (e is TableCustomer table)
            {
                var derivedTable = new DerivedTableCustomer();

                result = new ExprJoinedTable(
                    table,
                    ExprJoinedTable.ExprJoinType.Inner,
                    derivedTable,
                    table.CustomerId == derivedTable.CustomerId);
            }

            return result;
        });
}

await baseSelect!
    .Query(database,
        (r) =>
        {
            Console.WriteLine($"Id: {tableCustomer.CustomerId.Read(r)}");
        });

For simpler scenarios you can just use “With…” functions:

var tUser = new TableUser();

Console.WriteLine("Original expression:");
var expression = SelectTop(1, tUser.FirstName).From(tUser).Done();

await expression.QueryScalar(database);

expression = expression
    .WithTop(null)
    .WithSelectList(tUser.UserId, tUser.FirstName + " " + tUser.LastName)
    .WithWhere(tUser.UserId == 7);

Console.WriteLine("With changed selection list and filter:");
await expression.QueryScalar(database);

var tCustomer = new TableCustomer();
expression = expression
    .WithInnerJoin(tCustomer, on: tCustomer.UserId == tUser.UserId);

Console.WriteLine("With joined table");
await expression.QueryScalar(database);

Actual T-SQL:

--Original expression:
SELECT TOP 1 
    [A0].[FirstName] 
FROM [dbo].[User] [A0]

--With changed selection list  and filter:
SELECT 
    [A0].[UserId],
    [A0].[FirstName]+' '+[A0].[LastName] 
FROM [dbo].[User] 
    [A0] 
WHERE 
    [A0].[UserId]=7

--With joined table
SELECT 
    [A0].[UserId],
    [A0].[FirstName]+' '+[A0].[LastName] 
FROM [dbo].[User] 
    [A0] 
JOIN [dbo].[Customer] 
    [A1] ON 
    [A1].[UserId]=[A0].[UserId] 
WHERE 
    [A0].[UserId]=7

Serialization to XML

Each expression can be exported to a xml string and then restored back. It can be useful to pass expressions over network:

var tableUser = new TableUser(Alias.Empty);

var selectExpr = Select(tableUser.FirstName, tableUser.LastName)
    .From(tableUser)
    .Where(tableUser.LastName == "Sturman")
    .Done();

//Exporting
var stringBuilder = new StringBuilder();
using XmlWriter writer = XmlWriter.Create(stringBuilder);
selectExpr.SyntaxTree().ExportToXml(writer);

//Importing
XmlDocument document = new XmlDocument();
document.LoadXml(stringBuilder.ToString());
var restored = (ExprQuerySpecification)ExprDeserializer
    .DeserializeFormXml(document.DocumentElement!);

var result = await restored
    .QueryList(database, r => (tableUser.FirstName.Read(r), tableUser.LastName.Read(r)));

foreach (var name in result)
{
    Console.WriteLine(name);
}

This an example of the XML text:

<Expr typeTag="QuerySpecification">
   <SelectList>
      <SelectList0 typeTag="Column">
         <ColumnName typeTag="ColumnName">
            <Name>FirstName</Name>
         </ColumnName>
      </SelectList0>
      <SelectList1 typeTag="Column">
         <ColumnName typeTag="ColumnName">
            <Name>LastName</Name>
         </ColumnName>
      </SelectList1>
   </SelectList>
   <From typeTag="Table">
      <FullName typeTag="TableFullName">
         <DbSchema typeTag="DbSchema">
            <Schema typeTag="SchemaName">
               <Name>dbo</Name>
            </Schema>
         </DbSchema>
         <TableName typeTag="TableName">
            <Name>User</Name>
         </TableName>
      </FullName>
   </From>
   <Where typeTag="BooleanEq">
      <Left typeTag="Column">
         <ColumnName typeTag="ColumnName">
            <Name>LastName</Name>
         </ColumnName>
      </Left>
      <Right typeTag="StringLiteral">
         <Value>Sturman</Value>
      </Right>
   </Where>
   <Distinct>false</Distinct>
</Expr>

Serialization to JSON

The similar functionality exists for JSON (.Net Core 3.1+)

var tableUser = new TableUser(Alias.Empty);

var selectExpr = Select(tableUser.FirstName, tableUser.LastName)
    .From(tableUser)
    .Where(tableUser.LastName == "Sturman")
    .Done();

//Exporting
var memoryStream = new MemoryStream();
var jsonWriter = new Utf8JsonWriter(memoryStream);
selectExpr.SyntaxTree().ExportToJson(jsonWriter);

string json = Encoding.UTF8.GetString(memoryStream.ToArray());

//Importing
var restored = (ExprQuerySpecification)ExprDeserializer
    .DeserializeFormJson(JsonDocument.Parse(json).RootElement);

var result = await restored
    .QueryList(database, r => (tableUser.FirstName.Read(r), tableUser.LastName.Read(r)));

foreach (var name in result)
{
    Console.WriteLine(name);
}

This an example of the JSON text:

{
   "$type":"QuerySpecification",
   "SelectList":[
      {
         "$type":"Column",
         "ColumnName":{
            "$type":"ColumnName",
            "Name":"FirstName"
         }
      },
      {
         "$type":"Column",
         "ColumnName":{
            "$type":"ColumnName",
            "Name":"LastName"
         }
      }
   ],
   "From":{
      "$type":"Table",
      "FullName":{
         "$type":"TableFullName",
         "DbSchema":{
            "$type":"DbSchema",
            "Schema":{
               "$type":"SchemaName",
               "Name":"dbo"
            }
         },
         "TableName":{
            "$type":"TableName",
            "Name":"User"
         }
      }
   },
   "Where":{
      "$type":"BooleanEq",
      "Left":{
         "$type":"Column",
         "ColumnName":{
            "$type":"ColumnName",
            "Name":"LastName"
         }
      },
      "Right":{
         "$type":"StringLiteral",
         "Value":"Sturman"
      }
   },
   "Distinct":false
}

Serialization to Plain List

Also an expression can be exported into a list of plain entities. It might be useful if you want to store some expressions (e.g. "Favorites Filters") in a plain structure:

var tableUser = new TableUser(Alias.Empty);

ExprBoolean filter1 = tableUser.LastName == "Sturman";
ExprBoolean filter2 = tableUser.LastName == "Freeborne";

var tableFavoriteFilter = new TableFavoriteFilter();
var tableFavoriteFilterItem = new TableFavoriteFilterItem();

var filterIds = await InsertDataInto(tableFavoriteFilter, new[] {"Filter 1", "Filter 2"})
    .MapData(s => s.Set(s.Target.Name, s.Source))
    .Output(tableFavoriteFilter.FavoriteFilterId)
    .QueryList(database, r => tableFavoriteFilterItem.FavoriteFilterId.Read(r));

var filter1Items = 
    filter1.SyntaxTree().ExportToPlainList((i, id, index, b, s, value) =>
    FilterPlainItem.Create(filterIds[0], i, id, index, b, s, value));

var filter2Items = 
    filter2.SyntaxTree().ExportToPlainList((i, id, index, b, s, value) =>
    FilterPlainItem.Create(filterIds[1], i, id, index, b, s, value));

await InsertDataInto(tableFavoriteFilterItem, filter1Items.Concat(filter2Items))
    .MapData(s => s
        .Set(s.Target.FavoriteFilterId, s.Source.FavoriteFilterId)
        .Set(s.Target.Id, s.Source.Id)
        .Set(s.Target.ParentId, s.Source.ParentId)
        .Set(s.Target.IsTypeTag, s.Source.IsTypeTag)
        .Set(s.Target.ArrayIndex, s.Source.ArrayIndex)
        .Set(s.Target.Tag, s.Source.Tag)
        .Set(s.Target.Value, s.Source.Value)
    )
    .Exec(database);

//Restoring
var restoredFilterItems = await Select(tableFavoriteFilterItem.Columns)
    .From(tableFavoriteFilterItem)
    .Where(tableFavoriteFilterItem.FavoriteFilterId.In(filterIds))
    .QueryList(
        database,
        r => new FilterPlainItem(
        favoriteFilterId: tableFavoriteFilterItem.FavoriteFilterId.Read(r),
        id: tableFavoriteFilterItem.Id.Read(r),
        parentId: tableFavoriteFilterItem.ParentId.Read(r),
        isTypeTag: tableFavoriteFilterItem.IsTypeTag.Read(r),
        arrayIndex: tableFavoriteFilterItem.ArrayIndex.Read(r),
        tag: tableFavoriteFilterItem.Tag.Read(r),
        value: tableFavoriteFilterItem.Value.Read(r)));

var restoredFilter1 = (ExprBoolean)ExprDeserializer
    .DeserializeFormPlainList(restoredFilterItems.Where(fi =>
        fi.FavoriteFilterId == filterIds[0]));

var restoredFilter2 = (ExprBoolean)ExprDeserializer
    .DeserializeFormPlainList(restoredFilterItems.Where(fi =>
        fi.FavoriteFilterId == filterIds[1]));

Console.WriteLine("Filter 1");
await Select(tableUser.FirstName, tableUser.LastName)
    .From(tableUser)
    .Where(restoredFilter1)
    .Query(database,
        (r) =>
        {
            Console.WriteLine($"{tableUser.FirstName.Read(r)} {tableUser.LastName.Read(r)}");
        });

Console.WriteLine("Filter 2");
await Select(tableUser.FirstName, tableUser.LastName)
    .From(tableUser)
    .Where(restoredFilter2)
    .Query(database,
        (r) =>
        {
            Console.WriteLine($"{tableUser.FirstName.Read(r)} {tableUser.LastName.Read(r)}");
        });

Table Descriptors Scaffolding

SqExpress comes with the code-gen utility (it is located in the nuget package cache). It can read metadata form a database and create table descriptor classes in your code. It requires .Net Core 3.1+

Package Manager Console

SYNTAX
    Gen-Tables [-DbType] {mssql | mysql | pgsql} [-ConnectionString] <string> [-OutputDir <string>] [-TableClassPrefix <string>] [-Namespace <string>]

GenerateTables.cmd

@echo off
set root=%userprofile%\.nuget\packages\sqexpress

for /F "tokens=*" %%a in ('dir "%root%" /b /a:d /o:n') do set "lib=%root%\%%a"

set lib=%lib%\tools\codegen\SqExpress.CodeGenUtil.dll

dotnet "%lib%" gentables mssql "MyConnectionString" --table-class-prefix "Tbl" -o ".\Tables" -n "MyCompany.MyProject.Tables"

GenerateTables.sh

#!/bin/bash

lib=~/.nuget/packages/sqexpress/$(ls ~/.nuget/packages/sqexpress -r|head -n 1)/tools/codegen/SqExpress.CodeGenUtil.dll

dotnet $lib gentables mssql "MyConnectionString" --table-class-prefix "Tbl" -o "./Tables" -n "MyCompany.MyProject.Tables"

It uses Roslyn compiler so it does not overwrite existing files - it patched it with actual columns. All kind of changes like attributes, namespaces, interfaces will remain after next runs.

DTOs Scaffolding

You can add special attributes to column properties in table descriptors to provide information to the code-gen util to create (update) DTO classes with mappings:

public class TableUser : TableBase
{
    [SqModel("UserName", PropertyName = "Id")]
    public Int32TableColumn UserId { get; }

    [SqModel("UserName")]
    public StringTableColumn FirstName { get; }

    [SqModel("UserName")]
    public StringTableColumn LastName { get; }

    //Audit Columns
    [SqModel("AuditData")]
    public Int32TableColumn Version { get; }

    [SqModel("AuditData")]
    public DateTimeTableColumn ModifiedAt { get; }

    public TableUser(Alias alias) : base("dbo", "User", alias)
    {
        ...
    }
}

To run the code-gen util before a project building, just define the following property in the project file:

<Project ..,>
  <PropertyGroup>
    ...
    <SqModelGenEnable>true</SqModelGenEnable>
    ...
  </PropertyGroup>

The list of all code-generation parameters can be found here: SqExpress.props.

The code generation tool can also be run from the command line:

Package Manager Console

SYNTAX
    Gen-Models [-InputDir <string>] [-OutputDir <string>] [-Namespace <string>] [-NoRwClasses] [-NullRefTypes] [-CleanOutput] [-ModelType {ImmutableClass | Record}]  [<CommonParameters>]

GenerateModel.cmd

@echo off
set root=%userprofile%\.nuget\packages\sqexpress

for /F "tokens=*" %%a in ('dir "%root%" /b /a:d /o:n') do set "lib=%root%\%%a"

set lib=%lib%\tools\codegen\SqExpress.CodeGenUtil.dll

dotnet "%lib%" genmodels -i "." -o ".\Models" -n "SqExpress.GetStarted.Models" --null-ref-types

generate-model.sh

#!/bin/bash
lib=~/.nuget/packages/sqexpress/$(ls ~/.nuget/packages/sqexpress -r|head -n 1)/tools/codegen/SqExpress.CodeGenUtil.dll
dotnet $lib genmodels -i "." -o "./Models" -n "SqExpress.GetStarted.Models"

The result will be the following classes:

UserName.cs

public class UserName
{
    public UserName(int id, string firstName, string lastName)
    {
        this.Id = id;
        this.FirstName = firstName;
        this.LastName = lastName;
    }

    public static UserName Read(ISqDataRecordReader record, TableUser table)
    {
        return new UserName(id: table.UserId.Read(record), firstName: table.FirstName.Read(record), lastName: table.LastName.Read(record));
    }

    public int Id { get; }

    public string FirstName { get; }

    public string LastName { get; }

    public static TableColumn[] GetColumns(TableUser table)
    {
        return new TableColumn[]{table.UserId, table.FirstName, table.LastName};
    }

    public static IRecordSetterNext GetMapping(IDataMapSetter<TableUser, UserName> s)
    {
        return s.Set(s.Target.FirstName, s.Source.FirstName).Set(s.Target.LastName, s.Source.LastName);
    }

    public static IRecordSetterNext GetUpdateKeyMapping(IDataMapSetter<TableUser, UserName> s)
    {
        return s.Set(s.Target.UserId, s.Source.Id);
    }

    public static IRecordSetterNext GetUpdateMapping(IDataMapSetter<TableUser, UserName> s)
    {
        return s.Set(s.Target.FirstName, s.Source.FirstName).Set(s.Target.LastName, s.Source.LastName);
    }

    public UserName WithId(int id)
    {
        return new UserName(id: id, firstName: this.FirstName, lastName: this.LastName);
    }

    public UserName WithFirstName(string firstName)
    {
        return new UserName(id: this.Id, firstName: firstName, lastName: this.LastName);
    }

    public UserName WithLastName(string lastName)
    {
        return new UserName(id: this.Id, firstName: this.FirstName, lastName: lastName);
    }
}

and AuditData.cs

You can use them as follows:

var tUser = new TableUser();

var users = await Select(UserName.GetColumns(tUser))
    .From(tUser)
    .QueryList(database, r => UserName.Read(r, tUser));

foreach (var userName in users)
{
    Console.WriteLine($"{userName.Id} {userName.FirstName} {userName.LastName}");
}

Note: SqModel attribute can be also used for temporary and derived table descriptors.

Model Selection

The library contains a fluent api that helps selecting tuples of models inner or left joined.

SqModelSelectBuilder
    .Select(Model1.GetReader())
    .InnerJoin(
        Model2.GetReader(), 
        on: t=> t.Table.Id1 == t.JoinedTable1.Id1)
    .InnerJoin(
        Model3.GetReader(), 
        on: t=> t.JoinedTable2.Id2 == t.JoinedTable1.Id2)
    ...
    .InnerJoin(
        ModelN.GetReader(), 
        on: t=> t.JoinedTable(N-1).Id(N-1) == t.JoinedTable(N-2).Id(N-1)))
    .LeftJoin(
        Model(N+1).GetReader(), 
        on: t=> t.JoinedTableN.IdN == t.JoinedTable(N-1).IdN))
    ...
    .Get(
        filter: t=> <Boolean Expression>,
        order: t=><Order Expression>,
        tuple=> <Result Mapping>)
    .QueryList(database);

    ... or
    .Find(
        offset, pageSize,
        filter: t=> <Boolean Expression>,
        order: t=><Order Expression>,
        tuple=> <Result Mapping>)
    .QueryPage(database);

Example:

var page = await SqModelSelectBuilder
    .Select(ModelEmptyReader.Get<TableCustomer>())
    .LeftJoin(
        UserName.GetReader(), 
        on: t => t.Table.UserId == t.JoinedTable1.UserId)
    .LeftJoin(
        CompanyName.GetReader(), 
        on: t => t.Table.CompanyId == t.JoinedTable2.CompanyId)
    .Find(0,10,
        filter: null,
        order: t => Asc(
            IsNull(
                t.JoinedTable1.FirstName + t.JoinedTable1.LastName,
                t.JoinedTable2.CompanyName)
            ),
        r => (r.JoinedModel1 != null 
                ? r.JoinedModel1.FirstName + " "+ r.JoinedModel1.LastName 
                : null) 
            ??
            r.JoinedModel2?.Name ?? "Unknown")
    .QueryPage(database);

foreach (var name in page.Items)
{
    Console.WriteLine(name);
}

Using in ASP.Net

There is a demo ASP.Net project which is supposed to show how SqExpress can be used in a real web app.

The ideas:

Each API request uses only one sql connection which is stored in a connection storage;
The connection storage can create an instance of SqDatabase;
The connection storage and SqDatabase have “Scoped” lifecycle;
SqDatabase is used in entity repositories which are responsible for “Domain Logic”.

PostgreSQL

You can run all the scenarios using Postgres SQL (of course the actual sql will be different):

DbCommand NpgsqlCommandFactory(NpgsqlConnection connection, string sqlText)
{
    return new NpgsqlCommand(sqlText, connection);
}

const string connectionString = 
    "Host=localhost;Port=5432;Username=postgres;Password=test;Database=test";

using (var connection = new NpgsqlConnection(connectionString))
{
    using (var database = new SqDatabase<NpgsqlConnection>(
        connection: connection,
        commandFactory: NpgsqlCommandFactory,
        sqlExporter: new PgSqlExporter(builderOptions: SqlBuilderOptions.Default
            .WithSchemaMap(schemaMap: new[] {
                new SchemaMap(@from: "dbo", to: "public")}))))
    {
        ...
    }
}

Note: You need to add Npgsql package to your project.

MySQL

You also can run all the scenarios using My SQL:

DbCommand MySqlCommandFactory(MySqlConnection connection, string sqlText)
{
    return new MySqlCommand(sqlText, connection);
}

const string connectionString = 
    "server=127.0.0.1;uid=test;pwd=test;database=test";

using (var connection = new MySqlConnection(connectionString))
{
    using (var database = new SqDatabase<MySqlConnection>(
        connection: connection,
        commandFactory: MySqlCommandFactory,
        sqlExporter: new MySqlExporter(
            builderOptions: SqlBuilderOptions.Default)))
    {
        ...
    }
}

Note: You need to add MySql.Data or MySqlConnector package to your project.

Auto-Mapper

Since the DAL works on top the ADO you can use Auto-Mapper (if you like it):

var mapper = new Mapper(new MapperConfiguration(cfg =>
{
    cfg.AddDataReaderMapping();
    var map = cfg.CreateMap<IDataRecord, AllColumnTypesDto>();

    if (context.IsPostgresSql)
    {
        map
            .ForMember(nameof(table.ColByte), c => c.Ignore())
            .ForMember(nameof(table.ColNullableByte), c => c.Ignore());
    }
}));

var result = await Select(table.Columns)
    .From(table)
    .QueryList(context.Database, r => mapper.Map<IDataRecord, AllColumnTypesDto>(r));

(taken from "Test/SqExpress.IntTest/Scenarios/ScAllColumnTypes.cs")

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SqExpress

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Auto-Mapper