title: Trying to include Query within MongoDB MapReduce call
body: <p>I am trying to create a very basic map-reduce example that also incorporates a query in the MapReduce api call.  </p>
  
  <p>My collection has lots of entries formatted as follows:</p>
  
  <pre><code>{ "_id" : { "$binary" : "PdYV4WMTAEyYMQHXJZfzvA==", "$type" : "03" }, 
      "firstname" : "Matthew", 
      "surname" : "Chambers", 
      "email" : "" }
  </code></pre>
  
  <p>The code is as follows:</p>
  
  <pre><code>var map = @"
  function() {
      emit(this.surname, { count : 22 });
  }";
  var reduce = @"
  function(key, emitValues) {
      return { count : emitValues[0].count };
  }";
  
  List&lt;BsonValue&gt; contactIds = new List&lt;BsonValue&gt;();
  contactIds.Add(new Guid("A04FC88D-7BF7-443D-B5C3-EB11EE2B36DF"));
  contactIds.Add(new Guid("26B690B3-5ED7-47F4-A878-3906E28BBC58"));
  MongoDB.Driver.Builders.QueryConditionList queryList = MongoDB.Driver.Builders.Query.In("_id", BsonArray.Create(contactIds));
  //var mr = personCollection.MapReduce(map, reduce);// THIS WORKS!    
  var mr = personCollection.MapReduce(queryList, map, reduce); // THIS FAILS
  </code></pre>
  
  <p>It all works if I don't include the queryList in the MapReduce call.  However, if I do include the queryList then I get the following runtime error:</p>
  
  <blockquote>
    <p>Command 'mapreduce' failed: db assertion failure (response: { "assertion" : "'out' has to be a string or an object", "assertionCode" : 13606, "errmsg" : "db assertion failure", "ok" : 0 })
        at MongoDB.Driver.MongoDatabase.RunCommandAs[TCommandResult](IMongoCommand command) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoDatabase.cs:line 621 at MongoDB.Driver.MongoCollection.MapReduce(BsonJavaScript map, BsonJavaScript reduce, IMongoMapReduceOptions options) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCollection.cs:line 788 at MongoDB.Driver.MongoCollection.MapReduce(IMongoQuery query, BsonJavaScript map, BsonJavaScript reduce) in C:\work\10gen\mongodb\mongo-csharp-driver\Driver\Core\MongoCollection.cs:line 823 at HPSLucene.Models.Mongo.MapReduce() in C:\Inetpub\wwwroot\HPSLucene\HPSLucene\Models\Mongo.cs:line 158</p>
  </blockquote>
  
  <p>Anyone know what the problem is?  Thanks very much.</p>