Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (c *Collection) Find(query interface{}) *Query {
	session := c.Database.Session
	session.m.RLock()
	q := &Query{session: session, query: session.queryConfig}
	session.m.RUnlock()
	q.op.query = query
	q.op.collection = c.FullName
	return q
}
func (c *Collection) Find(query interface{}) *Query {
	session := c.Database.Session
	session.m.RLock()
	q := &Query{session: session, query: session.queryConfig}
	session.m.RUnlock()
	q.op.query = query
	q.op.collection = c.FullName
	return q
}
// Find prepares a query using the provided document.  The document may be a
// map or a struct value capable of being marshalled with bson.  The map
// may be a generic one using interface{} for its key and/or values, such as
// bson.M, or it may be a properly typed map.  Providing nil as the document
// is equivalent to providing an empty document such as bson.M{}.
//
// Further details of the query may be tweaked using the resulting Query value,
// and then executed to retrieve results using methods such as One, For,
// Iter, or Tail.
//
// In case the resulting document includes a field named $err or errmsg, which
// are standard ways for MongoDB to return query errors, the returned err will
// be set to a *QueryError value including the Err message and the Code.  In
// those cases, the result argument is still unmarshalled into with the
// received document so that any other custom values may be obtained if
// desired.
//
// Relevant documentation:
//
//     http://www.mongodb.org/display/DOCS/Querying
//     http://www.mongodb.org/display/DOCS/Advanced+Queries
//