Faactory.DbContext.Npgsql 0.6.1

ADO.NET Extensions

This project contains a set of extensions to help with managing multiple data sources, more specifically, inside a DI scenario.

Getting started

Before we can use the extensions, we need to register the context provider with our DI container. We'll have to install the appropriate package, depending on the provider we want to use; the following are currently supported

We'll use SqlServer as an example

dotnet add package Faactory.DbContext.SqlClient

We'll then register the provider and configure our databases; we can add as many contexts as we need.

IServiceCollection services = ...;

services.AddSqlDbContextProvider()
    .AddDbContext( "my-db", "connection_string" )
    .AddDbContext( "my-other-db", "connection_string" );

Wherever we need to get access to our database context, we'll use the injected IDbContextFactory instance to retrieve an IDbContext instance.

public class Example
{
    private readonly IDbContext mydb;

    public Example( IDbContextFactory dbContextFactory )
    {
        mydb = dbContextFactory.GetDbContext( "my-db" );
    }

    // ...
}

To construct a new connection, we'll retrieve it from the IDbContext instance.

public class Example
{
    private readonly IDbContext mydb;

    // ...

    public async Task DoSomethingAsync()
    {
        using ( var connection = mydb.GetDbConnection() )
        {
            await connection.OpenAsync();

            // ...
        }
    }
}

We can also construct the connection and open it all in one go.

public async Task DoSomethingAsync()
{
    using ( var connection = await mydb.OpenAsync() )
    {
        // ...
    }
}

From this point forward, we'll have a DbConnection instance ready to use. Please note that all DbConnection instances should be properly disposed after use. Most of the ADO implementations will pool connections and not properly disposing them can lead to exceeding the number of open connections (connection leaks).

NOTICE: Starting with version 0.6, the library has switched to use the DbConnection class instead of the IDbConnection interface. This was done mostly because the interface doesn't expose the async methods. Since DbConnection should be the base class for most (if not all) ADO.NET providers, this transition shouldn't cause any braking changes. Nonetheless, if you're using the IDbConnection interface, you'll have to update your code to use the DbConnection class instead.

Transactions

As an alternative to the DbConnection.BeginTransaction[Async] methods, there are extensions available to shorten the amount of code written. The UseTransaction[Async] methods take care of opening/reusing a connection, creating a transaction and gracefully disposing of it all when finished.

public async Task DoSomethingAsync()
{
    await mydb.UseTransactionAsync( async t =>
    {
        var sqlCommand = t.Connection.CreateCommand();

        // ...

        await t.CommitAsync();
    } );
}

If an exception is thrown, the transaction is automatically rolled back. We can also provide additional behaviour to when this happens.

public async Task DoSomethingAsync()
{
    await mydb.UseTransactionAsync( async t =>
    {
        var sqlCommand = t.Connection.CreateCommand();

        // ...

        await t.CommitAsync();
    }, ex =>
    {
        // handle exception
    } );
}

Health checks

The library also provides a set of health checks that verify the status of the database contexts. These health checks can be used with the ASP.NET Core health checks middleware.

IServiceCollection services = ...;

services.AddHealthChecks()
    .AddDbContext( "my-db" )
    .AddDbContext( "my-other-db" );

Command builder

The command builder is a helper class that can be used to build SQL commands. It provides a fluent interface to build a DbCommand instance. The builder can be accessed by calling the BuildCommand extension method on IDbContext or DbConnection instances.

private readonly IDbContext mydb;

// ...

/*
This example creates a command builder from the connection instance.
This is probably the most straightforward way to use the builder.
*/
public async Task UseBuilderFromConnectionAsync()
{
    using ( var connection = await mydb.OpenAsync() )
    {
        var command = connection.BuildCommand()
            .SetText( "SELECT * FROM table WHERE id = @id" )
            .AddParameter( "@id", 1 )
            .Build();

        using ( var reader = await command.ExecuteReaderAsync() )
        {
            // ...
        }
    }
}

/*
This example creates a command builder directly from the context instance.
Please note that in this caase, the command builder will ask for a connection
instance from the context, which means that you'll have to properly dispose of it after use.
*/
public async Task UseBuilderFromContextAsync()
{
    var command = mydb.BuildCommand()
        .SetText( "SELECT * FROM table WHERE id = @id" )
        .AddParameter( "@id", 1 )
        .Build();

    // ensure that the connection is properly disposed of after use
    using ( command.Connection )
    {
        await command.Connection.OpenAsync();

        using ( var reader = await command.ExecuteReaderAsync() )
        {
            // ...
        }
    }
}

Compatibility with Object Mappers

The library is compatible with most object mappers that use DbConnection or IDbConnection instances, such as Dapper, PetaPoco or Norm.net.