Entity Framework (EF) doesn’t support importing stored procedures that build result sets from dynamic queries or temporary tables. The reason for this is that, in order to import a stored procedure, EF needs to execute it. However, this could lead to unintended changes in the database.
Why EF Can’t Handle These Types of Stored Procedures
EF uses the following command before executing any stored procedure:
SET FMTONLY ON
This command ensures that the stored procedure will return only metadata about the columns in the result set, without actually executing the logic within the stored procedure. This prevents potential modifications in the database, but because the logic is not executed, any temporary tables or dynamically built queries are not returned, leaving the metadata empty.
Two Solutions to Work Around This Limitation
You have two options to work around this issue:
1. Define the Returned Complex Type Manually
You can define the complex type manually in EF to match the result set structure that the stored procedure is supposed to return. This would bypass the need for EF to execute the stored procedure to determine its metadata.
2. Use a Hack: Disable SET FMTONLY Temporarily
If you do not want to rewrite your stored procedure, you can use a hack by adding SET FMTONLY OFF at the beginning of the stored procedure. This will allow the stored procedure to execute its logic fully, including any dynamic queries or temporary tables.
However, be careful: do not allow the stored procedure to modify any data during this process, as this could execute changes in the database during the import process.
After successfully importing the stored procedure into EF, you should remove the SET FMTONLY OFF hack to prevent any unwanted data modification during further executions.
Important Notes
- Do not allow stored procedures to modify data when using the
SET FMTONLY OFFhack, as this can result in data modifications during the import process. - The solution is a temporary measure to bypass the limitations of EF when dealing with stored procedures that use dynamic queries or temporary tables.