Stored procedure. Check if constraint are used in another table - sql

Question

I get this error message:
The DELETE statement conflicted with the REFERENCE constraint
"FK_FieldMapper_Field". The conflict occurred in database "SCAM",
table "dbo.FieldMapper", column 'FieldID'.
I have some accesshelpers which has a given amount of fields. These Fields can be used by multiple accesshelpers..
When I delete an accesshelper, I need to check if the fields in the given accesshelper are used by other accesshelpers. If they are, I shall delete the accesshelper, but not the fields, as that would break other accesshelpers.
How do i do that?
This is what I have come up with on my own so far.
USE [SCAM]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[deleteAccessHelperById]
#Id int
AS
BEGIN
SET NOCOUNT ON;
DECLARE #projectIds TABLE (id int);
INSERT INTO #projectIds ([id]) SELECT dbo.AccessHelperMapper.ProjectID FROM dbo.AccessHelperMapper WHERE dbo.AccessHelperMapper.AccessHelperID = #Id;
DELETE dbo.AccessHelperMapper WHERE dbo.AccessHelperMapper.AccessHelperID = #Id;
DECLARE #fieldIds TABLE (id int);
INSERT INTO #fieldIds ([id]) SELECT dbo.FieldMapper.FieldID FROM dbo.FieldMapper WHERE dbo.FieldMapper.AccessHelperID = #Id;
DECLARE #AHfields TABLE (id int)
Insert into #AHfields
Select fids.id from dbo.FieldMapper, #fieldIds as fids
where dbo.FieldMapper.AccessHelperID != #Id
and fids.id != dbo.FieldMapper.FieldID;
delete dbo.FieldMapper where dbo.FieldMapper.AccessHelperID = #Id and dbo.FieldMapper.FieldID IN (SELECT d.id FROM #AHfields as d);
delete dbo.Field where dbo.Field.ID in (SELECT g.id FROM #AHfields as g);
delete dbo.AccessHelper where dbo.AccessHelper.ID = #Id;
END

Answer 1

Try the below code. Hope this is what you were looking for:
USE [SCAM]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[deleteAccessHelperById]
#Id int
AS
BEGIN
SET NOCOUNT ON;
DELETE dbo.AccessHelperMapper WHERE dbo.AccessHelperMapper.AccessHelperID = #Id;
DECLARE #fieldIds TABLE (id int);
INSERT INTO #fieldIds ([id]) SELECT dbo.FieldMapper.FieldID FROM dbo.FieldMapper WHERE dbo.FieldMapper.AccessHelperID = #Id
AND dbo.FieldMapper.FieldID NOT IN (SELECT DISTINCT dbo.FieldMapper.FieldID FROM dbo.FieldMapper WHERE dbo.FieldMapper.AccessHelperID != #Id);
delete dbo.FieldMapper where dbo.FieldMapper.AccessHelperID = #Id --and dbo.FieldMapper.FieldID IN (SELECT d.id FROM #fieldIds as d);
delete dbo.Field where dbo.Field.ID in (SELECT g.id FROM #fieldIds as g);
delete dbo.AccessHelper where dbo.AccessHelper.ID = #Id;
END

Answer 2

First of all you need a transaction because you have partial data changes which cannot be applied separately.
ALTER PROCEDURE [dbo].[deleteAccessHelperById]
#Id int
AS
BEGIN
SET NOCOUNT ON;
DECLARE #fieldIds TABLE (id int);
BEGIN TRY
BEGIN TRAN
DELETE ahm
FROM dbo.AccessHelperMapper ahm
WHERE ahm.AccessHelperID = #Id;
DELETE fm
OUTPUT DELETED.fieldID
INTO #fieldIds(id)
FROM dbo.FieldMapper fm
WHERE fm.AccessHelperID = #Id
DELETE f
FROM dbo.Field f
WHERE exists(select 1 from #fieldIDs fid where fid.ID = f.ID)
and not exists(
select 1 from dbo.FieldMapper fm
where fm.fieldID = f.ID
and fm.AccessHelperID != #ID -- redundant, may be removed.
)
DELETE ah
FROM dbo.AccessHelper ah
where ah.ID = #Id
COMMIT TRAN
END TRY
BEGIN CATCH
IF XACT_STATE() IN (1, -1)
ROLLBACK TRAN
THROW;
END CATCH
END