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by Jiří {x2} Činčura

SQL command when inserting M:N association with identity columns in the underlying table

18 Feb 2010 1 mins Databases in general, Entity Framework, MS SQL Server

Today I uncovered a magic command from Entity Framework v4 when you create M:N association and the underlying table is defined with both columns as identity and you insert there. I don’t what’s it good for, as this table in fact only stores the two IDs to connect other tables. But somebody may build some logic on identity there, sure.

When I first saw the command, I was completely stunned. I had no idea what’s going on there and whether I see there one or more commands. You can have fun too:

declare @generated_keys table([ID_A] int, [ID_B] int)
insert [dbo].[A_B]
output inserted.[ID_A], inserted.[ID_B] into @generated_keys
default values
select t.[ID_A], t.[ID_B]
from @generated_keys as g join [dbo].[A_B] as t on g.[ID_A] = t.[ID_A] and g.[ID_B] = t.[ID_B]
where @@ROWCOUNT > 0

As an old school guy I was first looking for semicolons and then later tried to decode it by “parsing” the content.

Isn’t it nice… 😃

Profile Picture Jiří Činčura is .NET, C# and Firebird expert. He's focused on data and business layers, language constructs, parallelism, databases and performance. He's Microsoft Most Valuable Professional and frequent speaker. You can read his articles, guides and tips and tricks at