Custom SQLite functions in Xamarin.iOS

Question

I am working on custom function of Sqlite on Xamarin.iOS. I got answer from here : Show markers on map within a given radius (Xamarin.Android) but I am running into issue of

Answer 1

I use the popular sqlite-net (by Frank A. Krueger) and it in turn uses SQLitePCLRaw.bundle_green and SQLitePCL.raw (both by Eric Sink).

Thus, you can use SQLitePCLRaw.ugly-based API to easily setup and access SQLite UDFs.

A Xamarin.iOS-based SQLite User Defined Function (UDF):

delegate void SQLiteCallback(sqlite3_context ctx, object user_data, sqlite3_value[] args);
[MonoPInvokeCallback(typeof(SQLiteCallback))]
static void UDFDistanceFunction(sqlite3_context ctx, object user_data, sqlite3_value[] args)
{
    double radius = 6367;
    var lat1 = raw.sqlite3_value_double(args[0]);
    var lng1 = raw.sqlite3_value_double(args[1]);
    var lat2 = raw.sqlite3_value_double(args[2]);
    var lng2 = raw.sqlite3_value_double(args[3]);
    var result = radius * 2 * Math.Asin(Math.Min(1, Math.Sqrt((Math.Pow(Math.Sin((lat2 * (Math.PI / 180) - lat1 * (Math.PI / 180)) / 2.0), 2.0) + Math.Cos(lat1 * (Math.PI / 180)) * Math.Cos(lat2 * (Math.PI / 180)) * Math.Pow(Math.Sin((lng2 * (Math.PI / 180) - lng1 * (Math.PI / 180)) / 2.0), 2.0)))));
    raw.sqlite3_result_double(ctx, result);
}

Usage:

Using sqlite-net-pcl to setup tables, load/update data, .....

SQLitePCL.raw.SetProvider(new SQLitePCL.SQLite3Provider_sqlite3());
var dbName = Path.Combine(Path.GetTempPath(), "StackOverflow.db");
var db = new SQLiteConnection(dbName, SQLiteOpenFlags.ReadWrite | SQLiteOpenFlags.Create, true);
db.CreateTable<BarLocations>();
db.Insert(new BarLocations()
{
    name = "FOOBAR", lat = 47.60357, lng = -122.3295
});

Using SQLitePCLRaw.ugly to create and query w/ a SQLite UDF

SQLitePCL.raw.SetProvider(new SQLitePCL.SQLite3Provider_sqlite3());
var dbName = Path.Combine(Path.GetTempPath(), "StackOverflow.db");
using (sqlite3 dbRaw = ugly.open(dbName))
{
    dbRaw.create_function("distance", 4, null, UDFDistanceFunction);
    double currentLatitude = 47.0;
    double currentLongitude = -122.0;
    var sql = $"SELECT * FROM barlocations WHERE distance('{currentLatitude.ToString()}', '{currentLongitude.ToString()}', barlocations.lat, barlocations.lng) <= 100 ;";
    var locs = dbRaw.query<BarLocations>(sql);
    foreach (var loc in locs)
    {
        Console.WriteLine(loc.name);
    }
}