[HowTo] Make User Defined Function In SQLite ADO.NET With C#

Sometimes we want to make a user-defined function and use it in our queries to the database. MS SQL Server and Oracle DBMS support user-defined functions, stored procedures, and transactions. Since SQLite is zero-configuration, serverless, and a single database file, SQLite doesn’t support user-defined functions natively (if you don’t know what SQLite is and how to use SQLite ADO.NET with C# please refer to this post). User-defined functions can be made outside of SQLite — that means you make a custom function with your own programming language and later that function can be bound to the SQLite core function.

SQLite ADO.NET fully supports user-defined functions, which means we can make our user-defined function in C# and later we can use the library from SQLite ADO.NET to bind it to the SQLite core function, then we can call that function in our queries to the database. To make a user-defined function in SQLite ADO.NET with C# is not hard — you just need a class which derives from the SQLiteFunction class and overrides the Invoke function. See the example below:

[SQLiteFunction(Name = "ToUpper", Arguments = 1, FuncType = FunctionType.Scalar)]
    public class ToUpper: SQLiteFunction
    {
        public override object Invoke(object[] args)
        {
            return args[0].ToString().ToUpper();
        }
    }

That’s it — when you compile and run your application, SQLite ADO.NET will automatically bind that user-defined function to the SQLite core function. And then you can use that function in your queries without a problem.

If you have any other tricks or tips about SQLite ADO.NET please feel free to leave a comment. Thanks and have a nice day!