Find a specified generic DbSet in a DbContext dyna

问题:

I have following classes and DbContext:

public class Order:BaseEntity
{
   public Number {get; set;}
}
Product:BaseEntity;
{
  public Name {get; set;} 
}

public class Context : DbContext
{
    ....
    public DbSet<Order> Orders { set; get; }
    public DbSet<Product> Products { set; get; }
    ....
}   

I have a list of objects that want to add to my context, too, but I don't know how can I find appropriate generic DbSet according each entity type dynamically.

IList<BaseEntity> list = new List<BaseEntity>();
Order o1 = new Order();
o1.Numner = "Ord1";
list.Add(o1);

Product p1 = new Product();
p1.Name = "Pencil";
list.Add(p1);

Context cntx = new Context();  
foreach (BaseEntity entity in list)
{
      cntx.Set<?>().Add(entity);         
}

How can I do that?

回答1:

DbContext has a method called Set, that you can use to get a non-generic DbSet, such as:

var someDbSet = this.Set(typeof(SomeEntity));

So in your case:

foreach (BaseEntity entity in list)
{
      cntx.Set(entity.GetType()).Add(entity);         
}

回答2:

The question does not specify EF version and the proposed answer does not work anymore for Entity Framework Core (DbContext does not have non-generic set method in EF core at least at the date of this answer).

Yet you can still have a working extension method using the answer of Jon Skeet to this question. My code is added below for convenience.

**Update: Added the generic function call as well returning IQueryable< T> thanks to comment from Shaddix.

    public static IQueryable Set(this DbContext context, Type T)
    {

        // Get the generic type definition
        MethodInfo method = typeof(DbContext).GetMethod(nameof(DbContext.Set), BindingFlags.Public | BindingFlags.Instance);

        // Build a method with the specific type argument you're interested in
        method = method.MakeGenericMethod(T);

        return method.Invoke(context, null) as IQueryable;
    }

    public static IQueryable<T> Set<T>(this DbContext context)
    {
        // Get the generic type definition 
        MethodInfo method = typeof(DbContext).GetMethod(nameof(DbContext.Set), BindingFlags.Public | BindingFlags.Instance);

        // Build a method with the specific type argument you're interested in 
        method = method.MakeGenericMethod(typeof(T)); 

        return method.Invoke(context, null) as IQueryable<T>;
    } 

回答3:

In addition to Pablo answer:

You can add a class to your project:

namespace System.Data.Entity
{
  public static class EntityFrameworkExtensions
  {
    public static IEnumerable<object> AsEnumerable(this DbSet set)
    {
      foreach (var entity in set)
        yield return entity;
    }
  }
}

This class add a Extention method AsEnumerable to DbSet instance and when you want to use it for example for Count or filter some row:

var someDbSet = this.Set(typeof(SomeEntity));
var count = (from a in someDbSet.AsEnumerable() select a).Count();