Temporarily disable all foreign key constraints

To disable foreign key constraints:

DECLARE @sql NVARCHAR(MAX) = N'';;WITH x AS (  SELECT DISTINCT obj =       QUOTENAME(OBJECT_SCHEMA_NAME(parent_object_id)) + '.'     + QUOTENAME(OBJECT_NAME(parent_object_id))   FROM sys.foreign_keys)SELECT @sql += N'ALTER TABLE ' + obj + ' NOCHECK CONSTRAINT ALL;' FROM x;EXEC sp_executesql @sql;

To re-enable:

DECLARE @sql NVARCHAR(MAX) = N'';;WITH x AS (  SELECT DISTINCT obj =       QUOTENAME(OBJECT_SCHEMA_NAME(parent_object_id)) + '.'     + QUOTENAME(OBJECT_NAME(parent_object_id))   FROM sys.foreign_keys)SELECT @sql += N'ALTER TABLE ' + obj + ' WITH CHECK CHECK CONSTRAINT ALL;' FROM x;EXEC sp_executesql @sql;

However, you will not be able to truncate the tables, you will have to delete from them in the right order. If you need to truncate them, you need to drop the constraints entirely, and re-create them. This is simple to do if your foreign key constraints are all simple, single-column constraints, but definitely more complex if there are multiple columns involved.

Here is something you can try. In order to make this a part of your SSIS package you'll need a place to store the FK definitions while the SSIS package runs (you won't be able to do this all in one script). So in some utility database, create a table:

CREATE TABLE dbo.PostCommand(cmd NVARCHAR(MAX));

Then in your database, you can have a stored procedure that does this:

DELETE other_database.dbo.PostCommand;DECLARE @sql NVARCHAR(MAX) = N'';SELECT @sql += N'ALTER TABLE ' + QUOTENAME(OBJECT_SCHEMA_NAME(fk.parent_object_id))   + '.' + QUOTENAME(OBJECT_NAME(fk.parent_object_id))    + ' ADD CONSTRAINT ' + fk.name + ' FOREIGN KEY ('    + STUFF((SELECT ',' + c.name    FROM sys.columns AS c         INNER JOIN sys.foreign_key_columns AS fkc         ON fkc.parent_column_id = c.column_id        AND fkc.parent_object_id = c.[object_id]    WHERE fkc.constraint_object_id = fk.[object_id]    ORDER BY fkc.constraint_column_id     FOR XML PATH(''), TYPE).value('.', 'nvarchar(max)'), 1, 1, '')+ ') REFERENCES ' + QUOTENAME(OBJECT_SCHEMA_NAME(fk.referenced_object_id))+ '.' + QUOTENAME(OBJECT_NAME(fk.referenced_object_id))+ '(' + STUFF((SELECT ',' + c.name    FROM sys.columns AS c         INNER JOIN sys.foreign_key_columns AS fkc         ON fkc.referenced_column_id = c.column_id        AND fkc.referenced_object_id = c.[object_id]    WHERE fkc.constraint_object_id = fk.[object_id]    ORDER BY fkc.constraint_column_id     FOR XML PATH(''), TYPE).value('.', 'nvarchar(max)'), 1, 1, '') + ');' FROM sys.foreign_keys AS fkWHERE OBJECTPROPERTY(parent_object_id, 'IsMsShipped') = 0;INSERT other_database.dbo.PostCommand(cmd) SELECT @sql;IF @@ROWCOUNT = 1BEGIN  SET @sql = N'';  SELECT @sql += N'ALTER TABLE ' + QUOTENAME(OBJECT_SCHEMA_NAME(fk.parent_object_id))    + '.' + QUOTENAME(OBJECT_NAME(fk.parent_object_id))     + ' DROP CONSTRAINT ' + fk.name + ';  ' FROM sys.foreign_keys AS fk;  EXEC sp_executesql @sql;END

Now when your SSIS package is finished, it should call a different stored procedure, which does:

DECLARE @sql NVARCHAR(MAX);SELECT @sql = cmd FROM other_database.dbo.PostCommand;EXEC sp_executesql @sql;

If you're doing all of this just for the sake of being able to truncate instead of delete, I suggest just taking the hit and running a delete. Maybe use bulk-logged recovery model to minimize the impact of the log. In general I don't see how this solution will be all that much faster than just using a delete in the right order.

In 2014 I published a more elaborate post about this here:

• Drop and Re-Create All Foreign Key Constraints in SQL Server

Use the built-in sp_msforeachtable stored procedure.

To disable all constraints:

EXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT ALL";

To enable all constraints:

EXEC sp_msforeachtable "ALTER TABLE ? WITH CHECK CHECK CONSTRAINT ALL";

To drop all the tables:

EXEC sp_msforeachtable "DROP TABLE ?";

A good reference is given at : http://msdn.microsoft.com/en-us/magazine/cc163442.aspxunder the section "Disabling All Foreign Keys"

Inspired from it, an approach can be made by creating a temporary table and inserting the constraints in that table, and then dropping the constraints and then reapplying them from that temporary table. Enough said here is what i am talking about

 SET NOCOUNT ON    DECLARE @temptable TABLE(       Id INT PRIMARY KEY IDENTITY(1, 1),       FKConstraintName VARCHAR(255),       FKConstraintTableSchema VARCHAR(255),       FKConstraintTableName VARCHAR(255),       FKConstraintColumnName VARCHAR(255),       PKConstraintName VARCHAR(255),       PKConstraintTableSchema VARCHAR(255),       PKConstraintTableName VARCHAR(255),       PKConstraintColumnName VARCHAR(255)        )    INSERT INTO @temptable(FKConstraintName, FKConstraintTableSchema, FKConstraintTableName, FKConstraintColumnName)    SELECT        KeyColumnUsage.CONSTRAINT_NAME,        KeyColumnUsage.TABLE_SCHEMA,        KeyColumnUsage.TABLE_NAME,        KeyColumnUsage.COLUMN_NAME     FROM        INFORMATION_SCHEMA.KEY_COLUMN_USAGE KeyColumnUsage          INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TableConstraints             ON KeyColumnUsage.CONSTRAINT_NAME = TableConstraints.CONSTRAINT_NAME    WHERE       TableConstraints.CONSTRAINT_TYPE = 'FOREIGN KEY'    UPDATE @temptable SET       PKConstraintName = UNIQUE_CONSTRAINT_NAME    FROM        @temptable tt          INNER JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS ReferentialConstraint             ON tt.FKConstraintName = ReferentialConstraint.CONSTRAINT_NAME    UPDATE @temptable SET       PKConstraintTableSchema  = TABLE_SCHEMA,       PKConstraintTableName  = TABLE_NAME    FROM @temptable tt       INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TableConstraints          ON tt.PKConstraintName = TableConstraints.CONSTRAINT_NAME    UPDATE @temptable SET       PKConstraintColumnName = COLUMN_NAME    FROM @temptable tt       INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE KeyColumnUsage          ON tt.PKConstraintName = KeyColumnUsage.CONSTRAINT_NAME    --Now to drop constraint:    SELECT       '       ALTER TABLE [' + FKConstraintTableSchema + '].[' + FKConstraintTableName + ']        DROP CONSTRAINT ' + FKConstraintName + '       GO'    FROM       @temptable    --Finally to add constraint:    SELECT       '       ALTER TABLE [' + FKConstraintTableSchema + '].[' + FKConstraintTableName + ']        ADD CONSTRAINT ' + FKConstraintName + ' FOREIGN KEY(' + FKConstraintColumnName + ') REFERENCES [' + PKConstraintTableSchema + '].[' + PKConstraintTableName + '](' + PKConstraintColumnName + ')       GO'    FROM       @temptable    GO