如何处理多个新添加的实体，这些实体依赖于具有外键约束的每个水獭 - EF6

Question

I had a bit of difficulties with getting the right title for this problem so I hope my explanation below will make it a bit clearer.

I am using EntityFramework 6 and I am doing multiple inserts within a function.

There are 3 different tables which get updated / inserted: table EntityMethod , EntityRoom and EntityRoomMethod . The table EntityRoomMethod has a foreign key relationship with the table EntityMethod .

In some cases, a EntityMethod row is missing and this is newly created by adding the object with entity framework:

if (mn == null)
{
    mn = new Method
    {
        ElementId = floorProgram.ElementId,
        ActionId = m.ActionId,
        ElementCount = m.ElementCount,
        ColorId = m.ColorId,
        IsBase = m.IsBase,
        IsHccp = m.IsHccp,
        TimeNorm = m.TimeNorm,
        Frequency5Id = m.Frequency5Id,
        MaterialId = m.MaterialId,
        ProductId = m.ProductId,
        MethodTypeId = m.MethodTypeId,
    };
}

In another part of code the Method foreign key (MethodId) of the EntityRoomMethod table is being set:

roomMethodObject.RightId = mn.Id; 

RightId is in this case the relationship with the EntityMethod table.

On a later point the other 2 table objects ( EntityRoom and EntityRoomMethod ) are also added ( DBSet.Add ) using EF.

The problem however is, that when the EntityMethod is newly added, it gets the Id value of 0 , because SaveChanges() is not yet executed. The foreign key reference in the EntityRoomMethod is therefor also being set to 0 .

When the function returns to the caller, the SaveChanges() is being executed and all 3 objects (representing the 3 tables) are being saved. This however will generate a FK error (because Id 0 does not exist obviously).

I tried to fix this by calling SaveChanges() after Adding the new Method (so directly in the function). This however will cause some other problems. In the end I have gotten multiple errors but I assume it all has to do with the same thing, the errors were the following:

1. Unable to determine the principal end of the 'Solution.Data.RoomMethod_Method' relationship. Multiple added entities may have the same primary key.
2. The property 'RightId' is part of the object's key information and cannot be modified.
3. Conflicting changes to the role x of the relationship y have been detected

So now the actual question: Is there an (easy) way to call SaveChanges() after all 3 entities have been added with EF but also handling the FK errors? Does this mean I have to generate the Id's myself? Or was the first approach better (Calling SaveChanges directly after adding the EntityMethod object).

For now I have some not-nice-looking solution with doing a direct INSERT statement after adding a new EntityMethod (using Dapper ). This kind-of works but I assume there is a better way wherein I can just use EF6.

PS calling SaveChanges() after adding the EntityMethod was basically the same by doing it with Dapper , however this generated some other errors while using Dapper it didn't generate those errors.

Answer 1

You can wrap several SaveChanges within a transaction, and EF (or probably SQL) will generate the required ids at each point, allowing you to reference them later on.

using(var transaction = _context.Database.BeginTransaction())
{
   var p1 = new Something { Name = "Fred" };
   _context.SaveChanges();

   var a2 = new Dependency { SomethingId = p1.Id }; <-- p1.Id now has an Id value
   _context.SaveChanges();

   var b3 = new OtherDependency { DependencyId = a2.Id };  <-- a2.Id now has an Id value
   _context.SaveChanges();

  transaction.Commit(); <-- All 3 changes are fully committed to the db at this point.
}