How to use Generic CRUD in Entity Framework using DI

Question

I wanna to try generic but I get some problem.

and this is my step

step 1. I create a database Model also inheritance class

    public class DBRepo { }
    public partial class UserAccount : DBRepo
    {
        public int Id { get; set; }
        public string Account { get; set; }
        public string Pwd { get; set; }
    }

step 2. I wish all CRUD action can using this interface. so I do this

public class DBServices
    {     
        public interface IDBAction<TEntity> where TEntity : DBRepo
        {
            void InsertData(TEntity entity);
        }

        public class dbCRUD<TEntity> : IDBAction<TEntity> where TEntity : DBRepo
        {
            private readonly CoreContext _db;
            private DbSet<TEntity> dbSet;
            public dbCRUD(CoreContext _db)
            {
                this._db = _db;
                this.dbSet = _db.Set<TEntity>();
            }

            public void InsertData(TEntity _entity)
            {
                this.dbSet.Add(_entity);
                this._db.SaveChanges();

            }
        }
    }

and then I usine ServiceProvider like

ServiceProvider provider = new ServiceCollection()
                               .AddSingleton<IDBAction<DBRepo>>()
                               .BuildServiceProvider();
        provider.GetService<IDBAction<DBRepo>>().InsertData(_ua);

and I'll get this error

Cannot instantiate implementation type ....

so I change to try other way like.

in Constructor

private readonly IDBAction<DBRepo> dBAction;
public HomeController( IDBAction<DBRepo> _dBAction)
{
   this.dBAction = _dBAction;
}

....
this.dBAction.InsertData(_ua);

sure.I get error again

InvalidOperationException: Unable to resolve service for type...

have some can teach me how to fix the problem?

-> Update

I try to change like but it's failed

ServiceProvider provider = new ServiceCollection()
                            .AddScoped<IDBAction<DBRepo>, dbCRUD<DBRepo>>()
                            .AddScoped<CoreContext>()
                                .BuildServiceProvider();

error same this

Unable to resolve service for type...

it's my DBContext

public virtual DbSet<UserAccount> UserAccount { get; set; }


        public CoreContext(DbContextOptions<CoreContext> options) 
            : base(options)
        {
        }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
               optionsBuilder.UseSqlServer(@"Connection String");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<UserAccount>(entity =>
            {
                entity.Property(e => e.Account).IsRequired();

                entity.Property(e => e.Pwd)
                    .IsRequired()
                    .HasMaxLength(20);
            });
        }

Am i wrong? You have a problem not with CRUD, but with Dependency Injection here ? — alerya
– alerya, Commented Mar 16, 2018 at 8:28
Sorry, you use DI in wrong way. Ideally .GetService<>() should be called only once in the application. Think about it and play with dependency injection to understand how it should work. — alerya
– alerya, Commented Mar 16, 2018 at 8:37

alsami · Accepted Answer · 2018-03-16 10:19:27Z

1

You are registering it in the wrong way. You must provide the implementation of your (generic) and also the DbContext must be registered.

ServiceProvider provider = new ServiceCollection()
                               .AddSingleton<IDBAction<DBRepo>, dbCRUD<DBRepo>>()
                               .BuildServiceProvider();

 provider.GetService<IDBAction<DBRepo>>().InsertData(_ua);

Also registering it as a singleton will cause problems with change-tracking of entity-framework. So you should register it like this:

ServiceProvider provider = new ServiceCollection()
                               .AddScoped<IDBAction<DBRepo>, dbCRUD<DBRepo>>()
.AddScoped<CoreContext>()
                                   .BuildServiceProvider();

 provider.GetService<IDBAction<DBRepo>>().InsertData(_ua);

You could also implement a real generic like this

public interface IEntity
{
   Guid Id { get; set; }
}

public class DbAction<TEntity> : IDbAction<TEntity> where TEntity: class, IEntity, new()
{
    public void InsertData(TEntity entity)
    {
        ...
    }
}

Now register it as a generic

ServiceProvider provider = new ServiceCollection()
                               .AddScoped(typeof(IDbAction<>), typeof(DbAction<>))
.AddScoped<CoreContext>()
                                   .BuildServiceProvider();

 provider.GetService<IDBAction<DBRepo>>().InsertData(_ua);

Small example, but would work.

Edit:

DbContextOptions must of course be passed to the DbContext for the IoC to work.

.AddDbContext<CoreContext>(options => options.UseSqlServer("my-conntection-string")); // change provider if necessary, this will only work with MS SQL Server

edited Mar 16, 2018 at 10:19

answered Mar 16, 2018 at 8:36

alsami

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7 Comments

鄭名宏 Over a year ago

Yes, look good, but also fail , I update my quection u can see . thk

alsami Over a year ago

You didn't read my answer properly, you are still missing the registration of DbContext. Also still using singletons.

鄭名宏 Over a year ago

DbContext alway null

alsami Over a year ago

Yeah you are not passing the DbContextOptions to the constructor of your DbContext. I updated the post. You should really learn to understand what is IoC and DI

鄭名宏 Over a year ago

Yes it's can work,But I have other question.in ConfigureServices I already Add DBContext. why I need add again in ServiceProvider

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