Stored procedure to remove FK of a given table - sql

Question

I need to create a stored procedure that:
Accepts a table name as a parameter
Find its dependencies (FKs)
Removes them
Truncate the table
I created the following so far based on http://www.mssqltips.com/sqlservertip/1376/disable-enable-drop-and-recreate-sql-server-foreign-keys/ . My problem is that the following script successfully does 1 and 2 and generates queries to alter tables but does not actually execute them. In another word how can execute the resulting "Alter Table ..." queries to actually remove FKs?
CREATE PROCEDURE DropDependencies(#TableName VARCHAR(50))
AS
BEGIN
SELECT 'ALTER TABLE ' + OBJECT_SCHEMA_NAME(parent_object_id) + '.[' + OBJECT_NAME(parent_object_id) + '] DROP CONSTRAINT ' + name
FROM sys.foreign_keys WHERE referenced_object_id=object_id(#TableName)
END
EXEC DropDependencies 'TableName'
Any idea is appreciated!
Update:
I added the cursor to the SP but I still get and error:
"Msg 203, Level 16, State 2, Procedure DropRestoreDependencies, Line 75
The name 'ALTER TABLE [dbo].[ChildTable] DROP CONSTRAINT [FK__ChileTable__ParentTable__745C7C5D]' is not a valid identifier."
Here is the updated SP:
CREATE PROCEDURE DropRestoreDependencies(#schemaName sysname, #tableName sysname)
AS
BEGIN
SET NOCOUNT ON
DECLARE #operation VARCHAR(10)
SET #operation = 'DROP' --ENABLE, DISABLE, DROP
DECLARE #cmd NVARCHAR(1000)
DECLARE
#FK_NAME sysname,
#FK_OBJECTID INT,
#FK_DISABLED INT,
#FK_NOT_FOR_REPLICATION INT,
#DELETE_RULE smallint,
#UPDATE_RULE smallint,
#FKTABLE_NAME sysname,
#FKTABLE_OWNER sysname,
#PKTABLE_NAME sysname,
#PKTABLE_OWNER sysname,
#FKCOLUMN_NAME sysname,
#PKCOLUMN_NAME sysname,
#CONSTRAINT_COLID INT
DECLARE cursor_fkeys CURSOR FOR
SELECT Fk.name,
Fk.OBJECT_ID,
Fk.is_disabled,
Fk.is_not_for_replication,
Fk.delete_referential_action,
Fk.update_referential_action,
OBJECT_NAME(Fk.parent_object_id) AS Fk_table_name,
schema_name(Fk.schema_id) AS Fk_table_schema,
TbR.name AS Pk_table_name,
schema_name(TbR.schema_id) Pk_table_schema
FROM sys.foreign_keys Fk LEFT OUTER JOIN
sys.tables TbR ON TbR.OBJECT_ID = Fk.referenced_object_id --inner join
WHERE TbR.name = #tableName
AND schema_name(TbR.schema_id) = #schemaName
OPEN cursor_fkeys
FETCH NEXT FROM cursor_fkeys
INTO #FK_NAME,#FK_OBJECTID,
#FK_DISABLED,
#FK_NOT_FOR_REPLICATION,
#DELETE_RULE,
#UPDATE_RULE,
#FKTABLE_NAME,
#FKTABLE_OWNER,
#PKTABLE_NAME,
#PKTABLE_OWNER
WHILE ##FETCH_STATUS = 0
BEGIN
-- create statement for dropping FK and also for recreating FK
IF #operation = 'DROP'
BEGIN
-- drop statement
SET #cmd = 'ALTER TABLE [' + #FKTABLE_OWNER + '].[' + #FKTABLE_NAME
+ '] DROP CONSTRAINT [' + #FK_NAME + ']'
EXEC #cmd
-- create process
DECLARE #FKCOLUMNS VARCHAR(1000), #PKCOLUMNS VARCHAR(1000), #COUNTER INT
-- create cursor to get FK columns
DECLARE cursor_fkeyCols CURSOR FOR
SELECT COL_NAME(Fk.parent_object_id, Fk_Cl.parent_column_id) AS Fk_col_name,
COL_NAME(Fk.referenced_object_id, Fk_Cl.referenced_column_id) AS Pk_col_name
FROM sys.foreign_keys Fk LEFT OUTER JOIN
sys.tables TbR ON TbR.OBJECT_ID = Fk.referenced_object_id INNER JOIN
sys.foreign_key_columns Fk_Cl ON Fk_Cl.constraint_object_id = Fk.OBJECT_ID
WHERE TbR.name = #tableName
AND schema_name(TbR.schema_id) = #schemaName
AND Fk_Cl.constraint_object_id = #FK_OBJECTID -- added 6/12/2008
ORDER BY Fk_Cl.constraint_column_id
OPEN cursor_fkeyCols
FETCH NEXT FROM cursor_fkeyCols INTO #FKCOLUMN_NAME,#PKCOLUMN_NAME
SET #COUNTER = 1
SET #FKCOLUMNS = ''
SET #PKCOLUMNS = ''
WHILE ##FETCH_STATUS = 0
BEGIN
IF #COUNTER > 1
BEGIN
SET #FKCOLUMNS = #FKCOLUMNS + ','
SET #PKCOLUMNS = #PKCOLUMNS + ','
END
SET #FKCOLUMNS = #FKCOLUMNS + '[' + #FKCOLUMN_NAME + ']'
SET #PKCOLUMNS = #PKCOLUMNS + '[' + #PKCOLUMN_NAME + ']'
SET #COUNTER = #COUNTER + 1
FETCH NEXT FROM cursor_fkeyCols INTO #FKCOLUMN_NAME,#PKCOLUMN_NAME
END
CLOSE cursor_fkeyCols
DEALLOCATE cursor_fkeyCols
END
FETCH NEXT FROM cursor_fkeys
INTO #FK_NAME,#FK_OBJECTID,
#FK_DISABLED,
#FK_NOT_FOR_REPLICATION,
#DELETE_RULE,
#UPDATE_RULE,
#FKTABLE_NAME,
#FKTABLE_OWNER,
#PKTABLE_NAME,
#PKTABLE_OWNER
END
CLOSE cursor_fkeys
DEALLOCATE cursor_fkeys
END
For running use:
EXEC DropRestoreDependencies dbo, ParentTable

Answer 1

Use a cursor to go through your SELECT results, populating a variable with the single column, and executing that query with EXEC(#YourVariable). Be sure to use parens around the variable!

Answer 2

The issue is that you are only preparing the SQL statement and not executing it (I think)
CREATE PROCEDURE DropDependencies(#TableName VARCHAR(50))
AS
BEGIN
DECLARE #SQL nvarchar(max)
SELECT #SQL = 'ALTER TABLE ' + OBJECT_SCHEMA_NAME(parent_object_id) + '.[' + OBJECT_NAME(parent_object_id) + '] DROP CONSTRAINT ' + name
FROM sys.foreign_keys WHERE referenced_object_id=object_id(#TableName)
EXEC #SQL
END
EXEC DropDependencies 'TableName'
Whenever using EXEC though from constructed strings, ensure you aren't vulnerable to SQL Injection attacks.

Answer 3

Try Out SP_ExecuteSQL or Exec. I see that you are using Exec. Perhaps SP_ExecuteSQL will work?