MongoDB Documentation, Release 3.0.4 DBRefs Background Format $ref $id $db Example Driver Support for DBRefs C The C driver contains no support for DBRefs. You can traverse references manually. C++ The C++ driver contains no support for DBRefs. You can traverse references manually. C# The C# driver supports DBRefs using the MongoDBRef 17 class and the FetchDBRef 18 method. Note: The order of fields in the DBRef matters, and you must use the above sequence when using a DBRef. The DBRef in this example points to a document in the creators collection of the users database that has ObjectId("5126bc054aed4daf9e2ab772") in its _id field. { "$ref" : <value>, "$id" : <value>, "$db" : <value> } Consider a document from a collection that stored a DBRef in a creator field: DBRef documents resemble the following document: Only some drivers support $db references. Contains the name of the database where the referenced document resides. The $id field contains the value of the _id field in the referenced document. The $ref field holds the name of the collection where the referenced document resides. DBRefs have the following fields: DBRefs are a convention for representing a document , rather than a specific reference type. They include the name of the collection, and in some cases the database name, in addition to the value from the _id field. Optional. { "_id" : ObjectId("5126bbf64aed4daf9e2ab771"), // .. application fields "creator" : { "$ref" : "creators", "$id" : ObjectId("5126bc054aed4daf9e2ab772"), "$db" : "users" } } $^{17}$https://api.mongodb.org/csharp/current/html/46c356d3-ed06-a6f8-42fa-e0909ab64ce2.htm $^{18}$https://api.mongodb.org/csharp/current/html/1b0b8f48-ba98-1367-0a7d-6e01c8df436f.htm 173 4.4. Data Model Reference