Is there an "Explain Query" for MongoDB Linq?

Question

Is there a way to run .explain() or equivalent on Linq queries? I would want to know

• The text of the actual JSON query
• The output of .explain() (indexes used, etc)
• It would also be nice to have the execution time of the query

Answer 1

You can get the Json easily enough if you have a query wrapper;

var qLinq = Query<T>.Where(x => x.name=="jim");
Console.WriteLine(qLinq.ToJson());

There's also an Explain() method on MongoCursor, so you could do this;

var exp = Collection.FindAs<T>(qLinq).Explain()
Console.WriteLine(exp.ToJson());

So if you want the time taken, "millis" is in there;

var msTaken = exp.First(x => x.Name == "millis").Value.AsInt32;

If you have an IQueryable, try something like this;

void Do(MongoCollection col, IQueryable iq)
{
        // Json Mongo Query
        var imq = (iq as MongoQueryable<Blob>).GetMongoQuery();
        Console.WriteLine(imq.ToString());

        // you could also just do;
        // var cursor = col.FindAs(typeof(Blob), imq);
        var cursor = MongoCursor.Create(typeof(Blob), col, imq, ReadPreference.Nearest);
        var explainDoc = cursor.Explain();

        Console.WriteLine(explainDoc);
    }//Do()