Create/Use User-defined functions in System.Data.SQLite?

Question

User-Defined Functions & Collating Sequences Full support for user-defined functions and collating sequences means that in many cases if SQLite doesn't have a feature, you can write it yourself in your favorite .NET language. Writing UDF's and collating sequences has never been easier

I spotted this bit on the C# SQLite ADO.NET provider l found here, and was having problems understanding the documentation on how to implement/use user-defined functions.

Could anyone explain how to, or provide any working examples for this lost newbie?

Jarrod Dixon · Accepted Answer · 2012-05-03 18:39:35Z

71

Robert Simpson has a great example of a REGEX function you can use in your sqlite queries:

// taken from http://sqlite.phxsoftware.com/forums/p/348/1457.aspx#1457
[SQLiteFunction(Name = "REGEXP", Arguments = 2, FuncType = FunctionType.Scalar)]
class MyRegEx : SQLiteFunction
{
   public override object Invoke(object[] args)
   {
      return System.Text.RegularExpressions.Regex.IsMatch(Convert.ToString(args[1]),Convert.ToString(args[0]));
   }
}

// example SQL:  SELECT * FROM Foo WHERE Foo.Name REGEXP '$bar'

edited May 3, 2012 at 18:39

answered Oct 5, 2008 at 23:33

Jarrod Dixon

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3 Comments

metadings Over a year ago

For reference, see this answer how to bind it to a SQLiteConnection.

Lemmes Over a year ago

Your answer is correct. But the example SQL won't use the defined SQLiteFunction but rather the built-in function. One would call SELECT * FROM foo WHERE REGEXP(name, 'mySearchText')

simonwo Over a year ago

@Lemmes – that isn't quite true, as the REGEXP operator is equivalent to the function call and thus will invoke the user-supplied function.

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