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Introduction

The Abp.EntityFrameworkCore NuGet package is used to integrate the Entity Framework (EF) Core ORM framework. After installing this package, you need to also add a DependsOn attribute for AbpEntityFrameworkCoreModule.

DbContext

EF Core requires you to define a class derived from DbContext. In ABP, we need to derive from the AbpDbContext as shown below:

public class MyDbContext : AbpDbContext
{
    public DbSet<Product> Products { get; set; }

    public MyDbContext(DbContextOptions<MyDbContext> options)
        : base(options)
    {
    }
}

The constructor should get a DbContextOptions<T> as shown above. The parameter name must be options. It's not possible to change it because ABP provides it as an anonymous object parameter.

Configuration

The Startup Class

Use the AddAbpDbContext method on the service collection in the ConfigureServices method as shown below:

services.AddAbpDbContext<MyDbContext>(options =>
{
    options.DbContextOptions.UseSqlServer(options.ConnectionString);
});

For non web projects, we will not have a Startup class. In this case, we can use the Configuration.Modules.AbpEfCore().AddDbContext method in our module class to configure the DbContext, shown below:

Configuration.Modules.AbpEfCore().AddDbContext<MyDbContext>(options =>
{
    options.DbContextOptions.UseSqlServer(options.ConnectionString);
});

We used the given connection string and Sql Server as the database provider. Normally, options.ConnectionString is the default connection string (see next section). However, ABP can use IConnectionStringResolver to determine it. This behaviour can be changed and the connection string can be determined dynamically. The action passed to AddDbContext is called whenever a DbContext instance will be created. You also have a chance to return different connection strings, conditionally.

Where do we set the default connection string?

In the module PreInitialize method

You can do it in the PreInitialize method of your module as shown below:

public class MyEfCoreAppModule : AbpModule
{
    public override void PreInitialize()
    {
        Configuration.DefaultNameOrConnectionString = GetConnectionString("Default");
        ...
    }
}

You can define the GetConnectionString method, which simply returns the connection string from a configuration file. This is generally in the appsettings.json file.

Repositories

Repositories are used to abstract data access from higher layers. See the repository documentation for more info. 

Default Repositories

Abp.EntityFrameworkCore implements default repositories for all the entities defined in your DbContext. You don't have to create repository classes to use predefined repository methods. Example:

public class PersonAppService : IPersonAppService
{
    private readonly IRepository<Person> _personRepository;

    public PersonAppService(IRepository<Person> personRepository)
    {
        _personRepository = personRepository;
    }

    public void CreatePerson(CreatePersonInput input)
    {        
        person = new Person { Name = input.Name, EmailAddress = input.EmailAddress };

        _personRepository.Insert(person);
    }
}

The PersonAppService contructor-injects IRepository<Person> and uses the Insert method. In this way, you can easily inject IRepository<TEntity> (or IRepository<TEntity, TPrimaryKey>) and use the predefined methods.

Custom Repositories

If standard repository methods are not sufficient, you can create custom repository classes for your entities.

Application Specific Base Repository Class

ASP.NET Boilerplate provides a base class EfCoreRepositoryBase to implement repositories easily. To implement the IRepository interface, you can simply derive your repository from this class. It's better to create your own base class that extends EfRepositoryBase. This way, you can easily add shared and common methods to your repositories. Here's an example base class for all the repositories of a SimpleTaskSystem application:

//Base class for all repositories in my application
public class SimpleTaskSystemRepositoryBase<TEntity, TPrimaryKey> : EfCoreRepositoryBase<SimpleTaskSystemDbContext, TEntity, TPrimaryKey>
    where TEntity : class, IEntity<TPrimaryKey>
{
    public SimpleTaskSystemRepositoryBase(IDbContextProvider<SimpleTaskSystemDbContext> dbContextProvider)
        : base(dbContextProvider)
    {
    }

    //add common methods for all repositories
}

//A shortcut for entities which have an integer Id
public class SimpleTaskSystemRepositoryBase<TEntity> : SimpleTaskSystemRepositoryBase<TEntity, int>
    where TEntity : class, IEntity<int>
{
    public SimpleTaskSystemRepositoryBase(IDbContextProvider<SimpleTaskSystemDbContext> dbContextProvider)
        : base(dbContextProvider)
    {
    }

    //do not add a method here, add it to the class above (because this class inherits it)
}

Note that we're inheriting from EfCoreRepositoryBase<SimpleTaskSystemDbContext, TEntity, TPrimaryKey>. This sets ASP.NET Boilerplate to use the SimpleTaskSystemDbContext in our repositories.

By default, all repositories for your given DbContext (SimpleTaskSystemDbContext in this example) are implemented using EfCoreRepositoryBase. You can replace it with your own repository base class by adding the AutoRepositoryTypes attribute to your DbContext as shown below:

[AutoRepositoryTypes(
    typeof(IRepository<>),
    typeof(IRepository<,>),
    typeof(SimpleTaskSystemEfRepositoryBase<>),
    typeof(SimpleTaskSystemEfRepositoryBase<,>)
)]
public class SimpleTaskSystemDbContext : AbpDbContext
{
    ...
}
Custom Repository Example

To implement a custom repository, just derive it from your application specific base repository class like the one we created above.

Assume that we have a Task entity that can be assigned to a Person (entity). We also have a Task which has a State (new, assigned, completed... and so on). We may need to write a custom method to get the list of Tasks with some conditions and include the AssisgnedPerson property, pre-fetched (included), in a single database query. See the following code:

public interface ITaskRepository : IRepository<Task, long>
{
    List<Task> GetAllWithPeople(int? assignedPersonId, TaskState? state);
}

public class TaskRepository : SimpleTaskSystemRepositoryBase<Task, long>, ITaskRepository
{
    public TaskRepository(IDbContextProvider<SimpleTaskSystemDbContext> dbContextProvider)
        : base(dbContextProvider)
    {
    }

    public List<Task> GetAllWithPeople(int? assignedPersonId, TaskState? state)
    {
        var query = GetAll();

        if (assignedPersonId.HasValue)
        {
            query = query.Where(task => task.AssignedPerson.Id == assignedPersonId.Value);
        }

        if (state.HasValue)
        {
            query = query.Where(task => task.State == state);
        }

        return query
            .OrderByDescending(task => task.CreationTime)
            .Include(task => task.AssignedPerson)
            .ToList();
    }
}

We first defined ITaskRepository and then implemented it. The GetAll() method returns IQueryable<Task>. We then add some Where filters using the given parameters. Finally, we call ToList() to get the list of Tasks.

You can also use the Context object in the repository methods to reach your DbContext and directly use Entity Framework APIs. 

Note: Define the custom repository interface in the domain/core layer, implement it in the EntityFrameworkCore project for layered applications. That way, you can inject the interface from any project without referencing EF Core.

Replacing the Default Repositories

Even if you created a TaskRepository as shown above, any class can still inject IRepository<Task, long> and use it. That's not a problem in most cases. But what if you did an override on a base method in your custom repository? Say that you have overidden Delete method in your custom repository to add a custom behaviour on delete. If a class injects IRepository<Task, long> and usea the default repository to Delete a task, your custom behaviour will not work. To overcome this issue, you can replace your custom repository implementation with the default one like shown below:

Configuration.ReplaceService<IRepository<Task, Guid>>(() =>
{
    IocManager.IocContainer.Register(
        Component.For<IRepository<Task, Guid>, ITaskRepository, TaskRepository>()
            .ImplementedBy<TaskRepository>()
            .LifestyleTransient()
    );
});

We registered the TaskRepository for IRepository<Task, Guid>, ITaskRepository and TaskRepository. This way, any one of these can be injected to use the TaskRepository.

Repository Best Practices

  • Use the default repositories wherever it's possible. You can use a default repository even if you have a custom repository for an entity (if you are using the standard repository methods).
  • Always create the repository base class for your application for custom repositories, as defined above.
  • Define interfaces for your custom repositories in the domain layer (.Core project in the startup template). Then define the custom repository classes in the .EntityFrameworkCore project if you want to abstract EF Core from your domain/application.

Other Database Integrations

This document and the examples are based on using MS SQL Server. The following documents can be followed for different database integrations.