Registering nicknames for document store data source
For each document store server definition that you register, you must register a nickname for each collection that you want to access. Use these nicknames, instead of the names of the data source objects, when you query the document store data source servers.
When you register a nickname on a document store data source, the federated server establishes a mapping between the federated server columns and the fields of document store document. The federated server does not create the mapping. Therefore, you must manually create the mapping through nickname. This is a big difference to relational database. Nickname is a mechanism to resolve column and JSON document field mapping. While creating nickname, you can specify which field maps to which column, and specify the column type according to the value of JSON document field.
For different document store data sources, there are some small differences for creating nickname statement. For MongoDB and CouchDB please refer to the example as below: