Use DI in Data Access Layer with ApplicationDbContext (netcore 2.0)

Question

I have some problem with DI (Dependancy Injection). My project is on netcore 2.0 and has few layers (standard N-Tier Architecture). I'm trying to move EF Core 2 from Presentation Layer to Data Access Layer and I have created the following classes in DAL:

namespace MyProject.Infrastructure.Implementation.MySql.Contexts 
{
    public class ApplicationDbContext : DbContext
    {
        private readonly IConfiguration _configuration;

        public ApplicationDbContext(IConfiguration configuration)
        {
            _configuration = configuration;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder     optionsBuilder)
        {
            optionsBuilder.UseMySql(
                Configuration.GetConnectionString("MySql")
            );
        }

        public DbSet<Test> Test { get; set; }
    }
}

Then I prepared base class for all DAL engines:

namespace MyProject.Infrastructure.Implementation.MySql
{
    public class BaseEngine : IBaseEngine
    {
        private readonly ApplicationDbContext _context;

        protected ApplicationDbContext Db => _context;

        public BaseEngine(ApplicationDbContext context)
        {
            _context = context;
        }
    }
}

So, my common engine should look like this:

namespace MyProject.Infrastructure.Implementation.MySql
{
    public class TestEngine : BaseEngine
    {
        public List<Test> GetTestList()
        {   
            return Db.Test.ToList();
        }
    }
}

The problem is that I get error, BaseEngine needs parameter to be passed in constructor and I don't want to create all instances manually, I need somehow use Dependancy Injection that automatically creates instances of ApplicationDbContext and IConfiguration when BaseEngine and ApplicationDbContext will be created..

Any ideas?

Joe Wilson · Accepted Answer · 2018-02-12 16:42:52Z

2

Create a public interface for ApplicationDbContext, like IApplicationDbContext. Put that in the constructor for BaseEngine instead of the concrete class. Make the BaseEngine constructor protected. The BaseEngine constructor should look like:

protected BaseEngine(IApplicationDbContext context)

Then, since TestEngine is derived from BaseEngine, and BaseEngine requires a constructor argument, you have to pass that in from the TestEngine constructor like:

public TestEngine(IApplicationDbContext context) : base(context)

answered Feb 12, 2018 at 16:42

Joe Wilson

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