Complex queries

We now know how to convert DBObject instances to custom Scala classes. In this section, you will learn how to construct queries that only return a subset of the documents in the collection.

In the previous section, you learned to retrieve all the documents in a collection as follows:

scala> val objs = collection.find().toList
List[DBObject] = List({ "_id" : { "$oid" : "56365cec46f9534fae8ffd7f"} ,...

The collection.find() method returns an iterator over all the documents in the collection. By calling .toList on this iterator, we materialize it to a list.

We can customize which documents are returned by passing a query document to the .find method. For instance, we can retrieve documents for a specific login name:

scala> val query = DBObject("login" -> "mojombo")
query: DBObject = { "login" : "mojombo"}

scala> val objs = collection.find(query).toList
List[DBObject] = List({ "_id" : { "$oid" : "562e922546f953739c43df02"} , "login" : "mojombo",...

MongoDB queries...