Delete all entities in Entity Framework

Question

I want to delete content of all tables (all entities) using Entity Framework 4+. How can this be done?

Answer 1

I would like to try to improve the great answer of @Wojciech Markowski.

If you are lazy like me and don't want to check for foreign keys constraints, you can use this method:

        private void ClearDatabase(TContext context)
    {
            // disable all foreign keys
            //context.Database.ExecuteSqlCommand("EXEC sp_MSforeachtable @command1 = 'ALTER TABLE ? NOCHECK CONSTRAINT all'");

            List tableNames = context.Database.SqlQuery("SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE' AND TABLE_NAME NOT LIKE '%Migration%'").ToList();

            for (int i = 0; tableNames.Count>0; i++)
            {
                try
                {
                    context.Database.ExecuteSqlCommand(string.Format("DELETE FROM {0}", tableNames.ElementAt(i % tableNames.Count)));
                    tableNames.RemoveAt(i % tableNames.Count);
                    i = 0;
                }
                catch { } // ignore errors as these are expected due to linked foreign key data             
            }


            context.SaveChanges();
    }

ClearDatabase method goes over the list of tables and clean them. if FK constraint is found then catch the exception and move on to the next table. at the end all tables will be deleted.

Moreover, if you don't mind to loose all the FK constraints, you can disable all of them by the line:

context.Database.ExecuteSqlCommand("EXEC sp_MSforeachtable @command1 = 'ALTER TABLE ? NOCHECK CONSTRAINT all'");

One thing more: If you want to delete all tables and not just clear them, then replace the line:

context.Database.ExecuteSqlCommand(string.Format("DELETE FROM {0}", tableNames.ElementAt(i % tableNames.Count)));

with:

context.Database.ExecuteSqlCommand(string.Format("DROP TABLE {0}", tableNames.ElementAt(i % tableNames.Count)));

I personally checked this answer on Entity Framework 6 with code-first migration.

EDIT: better version:

        private void ClearDatabase(MrSaleDbContext context)
    {
        //Optional: disable all foreign keys (db-schema will be loosed).
        //context.Database.ExecuteSqlCommand("EXEC sp_MSforeachtable @command1 = 'ALTER TABLE ? NOCHECK CONSTRAINT all'");

        List tableNames = context.Database.SqlQuery("SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE' AND TABLE_NAME NOT LIKE '%Migration%' AND TABLE_NAME NOT LIKE 'AspNet%'").ToList();

        for (int i = 0; tableNames.Count > 0; i++)
        {
            try
            {
                //To delete all tables and not just clean them from data, replace "DELETE FROM {0}" in "DROP TABLE {0}":
                context.Database.ExecuteSqlCommand(string.Format("DELETE FROM {0}", tableNames.ElementAt(i % tableNames.Count)));
                tableNames.RemoveAt(i % tableNames.Count);
                i = -1; //flag: a table was removed. in the next iteration i++ will be the 0 index.
            }
            catch (System.Data.SqlClient.SqlException e)   // ignore errors as these are expected due to linked foreign key data    
            {                    
                if ((i % tableNames.Count) == (tableNames.Count - 1))
                {
                    //end of tables-list without any success to delete any table, then exit with exception:
                    throw new System.Data.DataException("Unable to clear all relevant tables in database (foriegn key constraint ?). See inner-exception for more details.", e);
                }

            }

        }

the if statement in catch block checks whether i reached the last index of the tables-list without deleting any table. In that case, instead of going in an infinite loop, throw exception and exit the for.