Use INSERT w/OUTPUT Instead of INSERT+SELECT

Entity Framework Core’s SQL Server provider (at least, as of v. 1.1.0) follows each INSERT statement with a SELECT statement that fetches database-generated values and verifies the inserted row count.

Proposal

Eliminate the SELECT statement. Instead:

• Fetch database-generated values using an OUTPUT clause on the INSERT statement.
• Rely on the database provider to throw an exception of the INSERT fails instead of verifying inserted row count (looks like was supposed to have been implemented per #2131).

Examples

Currently (EF Core 1.1.0)

-- Table w/identity column:
SET NOCOUNT ON;
INSERT INTO [TestTable1] ([Data])
VALUES (@p0);
SELECT [Id]
FROM [TestTable1]
WHERE @@ROWCOUNT = 1 AND [Id] = scope_identity();

-- Table w/identity and default value (`DEFAULT(GETDATE())`) columns:
SET NOCOUNT ON;
INSERT INTO [TestTable2] ([Data])
VALUES (@p0);
SELECT [Id], [HasDefaultValue]
FROM [TestTable2]
WHERE @@ROWCOUNT = 1 AND [Id] = scope_identity();

Proposed Simplification

-- Table w/identity column:
SET NOCOUNT ON;
INSERT INTO [TestTable1] ([Data])
    OUTPUT INSERTED.[Id]
VALUES (@p0);

-- Table w/identity and default value (`DEFAULT(GETDATE())`) columns:
SET NOCOUNT ON;
INSERT INTO [TestTable2] ([Data])
    OUTPUT INSERTED.[Id], INSERTED.[HasDefaultValue]
VALUES (@p0);

Example Code

Example.zip

Further technical details

EF Core version: 1.1.0 Operating system: Windows 10 Visual Studio version: VS 2015

[Coder3333]

I am getting heavy deadlocking issues from the 2 step approach, and this is when I am only doing 2 simultaneous inserts into a table. If EF were using the output clause to get the identity, instead of a separate query, I do not think I would have the deadlock issues. Would it make sense to add an option for developers to choose how the insert is handled for folks that are not concerned about triggers?

[ErikEJ]

@roji Be careful out there: https://www.mssqltips.com/sqlservertip/3074/use-caution-with-sql-servers-merge-statement/