Question

I’m trying to generate a query that finds all large, red things with a cost greater than 3.

This query seems to be what I’m after:

{ "color" : "red", "size" : "large", "cost" : { "$gt" : 3.0 } }

But, I am unable to find an elegant way to create the cost condition using the official MongoDB CSharp Driver. This is one hack which seems to create the query:

QueryConditionList gt = Query.GT("cost", BsonDouble.Create(3));

QueryDocument query = new QueryDocument();
query.Add("color", "red");
query.Add("size", "large");
query.Add(gt.ToBsonDocument().Elements);

List<BsonDocument> results = events.Find(query).ToList();

Another way to do it which seems to work is like this:

QueryDocument query = new QueryDocument();
query.Add("color", "red");
query.Add("size", "large");
query.Add("cost", new BsonDocument("$gt", BsonDouble.Create(3)));

List<BsonDocument> results = events.Find(query).ToList();

Are either of these approaches a good way to accomplish this? Is there another?

I need to use techniques which allow me to dynamically build the query and add fields that will be involved in the query. I was hoping to find a way to add a condition via query.Add( ) but I don’t know if that is possible.

Any help is appreciated.

Answer 1

You can use the Query builder throughout, like so:

var query = Query.And(
              Query.EQ("color", "red"), 
              Query.EQ("size", "large"), 
              Query.GT("cost", 3)
            );

update Sorry, I see what you’re asking, now.

You could do something like this, also:

int i = 0;
var qc = QueryComplete[3];
qc[i++] = Query.EQ("color", "red");
qc[i++] = Query.EQ("size", "large");
qc[i++] = Query.GT("cost", 3);
var query = Query.And(qc);

This way, you can still use the builder methods and have it be dynamic.