GUIDs vs. ObjectID

CartoPac supports relationships through GUIDs but does not support relationships through the use of any automatically incremented field such as Esri's ObjectID fields.  

Esri's ArcGIS software automatically creates a unique field in each table and feature, which is used as the feature or table's primary identifying field, or "primary key".  This field is an integer field that increases by one for every newly created record in the feature or table and is called ObjectID. While it is possible to create relationships between Esri's ArcGIS features and tables using the ObjectID field and a related integer field such as RelatedID, CartoPac does not recommend this and strongly cautions against such a setup.

Using ObjectID in relational data models is not supported.

ObjectID's are overwritten at the time a record is loaded into an ArcGIS database. Because CartoPac is often utilized on multiple devices simultaneously, the potential exists for two field users to download a project and then collect data at the same time.  Both users' newly collected features may create the same auto-numbered ObjectID on their devices. One of them will be correctly overwritten by the database when uploading a project, while the other(s) would be incorrectly overwritten, causing some mixing of related records as well as a loss of relationship.