DbContext SaveChanges Order of Statement Execution

问题

I have a table that has a unique index on a table with an Ordinal column. So for example the table will have the following columns:

TableId, ID1, ID2, Ordinal

The unique index is across the columns ID1, ID2, Ordinal.

The problem I have is that when deleting a record from the database I then resequence the ordinals so that they are sequential again. My delete function will look like this:

    public void Delete(int id)
    {
        var tableObject = Context.TableObject.Find(id);
        Context.TableObject.Remove(tableObject);
        ResequenceOrdinalsAfterDelete(tableObject);
    }

The issue is that when I call Context.SaveChanges() it breaks the unique index as it seems to execute the statements in a different order than they were passed. For example the following happens:

1. Resequence the Ordinals
2. Delete the record

Instead of:

1. Delete the record
2. Resequence the Ordinals

Is this the correct behaviour of EF? And if it is, is there a way of overriding this behaviour to force the order of execution?

If I haven't explained this properly, please let me know...

回答1:

Order of commands is completely under control of EF. The only way how you can affect the order is using separate SaveChanges for every operation:

public void Delete(int id)
{
    var tableObject = Context.TableObject.Find(id);
    Context.TableObject.Remove(tableObject);
    Context.SaveChanges();
    ResequenceOrdinalsAfterDelete(tableObject);
    Context.SaveChanges();
}

You should also run that code in manually created transaction to ensure atomicity (=> TransactionScope).

But the best solution would probably be using stored procedure because your resequencing have to pull all affected records from the database to your application, change their ordinal and save them back to the database one by one.

Btw. doing this with database smells. What is the problem with having a gap in your "ordinal" sequence?

来源：https://stackoverflow.com/questions/7335582/dbcontext-savechanges-order-of-statement-execution