Subscription for integrating external data from external system

Technologies are described herein for integrating external data from an external system into a client system. A subscription filed is selected. The subscription filed may include a read method and a query method. The read method may define fields of a client cache operating on the client system. The query method may be executed to retrieve, from the external system, field values corresponding to at least a subset of the fields. Upon executing the query method, the read method may also be executed to retrieve, from the external system, additional field values corresponding to a remaining subset of the fields that were not retrieved by executing the query method. The client cache is populated with the field values and the additional field values according to the fields.