实体框架6 SaveChanges导致唯一约束异常

Question

I'm getting a unique constraint violation when trying to do SaveChanges() on my EF.

There are two columns, ID and Order . The unique constraint is on those two columns.

I'm updating the order (swapping two of the values).

However, when I do SaveChanges() I get a DBUpdateExcception saying I've violated the unique constraint - but I haven't! I've just swapped the order .

Name | ID | Order
BH   | 49 | 1
JK   | 49 | 2

So in code, it now looks like this (and I've checked the EF in the debugger)

Name | ID | Order
BH   | 49 | 2
JK   | 49 | 1

As I said though, when I do SaveChanges() I get an exception.

I don't know if there is a problem with my model in visual studio 2015 (have to set a property or something to allow updates?). The problem seems to me to be that "it" isn't doing the update correctly.

Appreciate any help!

Answer 1

EntityFramework updates one row at a time. So by switching the Order value of the two objects and calling SaveChanges() It first fires something like this:

UPDATE TABLENAME SET [Order] = 2 WHERE [TABLENAME].[ID] = 49 AND [TABLENAME].[Order] = 1

If this update would be executed, you would have two rows in the table with the same values in the unique constraint. This is why you get the error.