I tried to execute this query in xamarin
SELECT * FROM GPSPoint WHERE SQRT( POW({0}-lat,2) + POW({1}-lng,2) ) < 5*5
But it gave me the error message
SQLite.SQLiteException: no such function: SQRT
And after searching I found that Android developers can use the sqlite3_create_function method to create new functions in SQLite.
How can I do the same thing in xamarin?
In the following example i make my custom sqlite function called MySqliteAdd , which has two arguments as input and their sum as a result
[SqliteFunction(FuncType = FunctionType.Scalar, Arguments = 2, Name = "MySqliteAdd")]
public class MySqliteAdd : SqliteFunction
{
public override object Invoke(object[] args){
return System.Convert.ToInt32(args[0]) + System.Convert.ToInt32(args[1]);
}
}
You can use it in a sqlite query like below
Select MySqliteAdd(25,35)
which will give you a result of 60
finally you have to register the function before you initialise your connection
SqliteFunction.RegisterFunction(typeof(MySqliteAdd));
WHERE col = valuevar query = conn.Query<GPSPoint>(string.Format("SELECT * FROM GPSPoint WHERE SQRT( POW({0}-lat,2) + POW({1}-lng,2) ) < 5*5", lat, lng));