I am reading geodatabase using ESRI File reader and this geodatabase contains feature classes with relationship classes. I am trying to write them as it is to another geodatabase. The problem is relationship classes are not created in output geodatabase.
A limitation of FME is that it cannot create relationship classes, but rather assumes they exist in the geodatabase already.
In the introduction of Writing Geodatabase Relationship Classes, it states:
it is assumed that the relationships have already been created in ArcGIS. This is required, as FME cannot create the relationships, but merely populate them.
Something that I've done in the past is to export the schema as an XML Workspace document from the file geodatabase in ArcMap and import that into the new geodatabase. This creates all the tables, feature classes and relationship classes, and then use FME to populate as required.
Be careful if your relationship classes are using GlobalID as the primary key. If so, FME will create a new one when it writes the new feature in the new geodatabase - dropping any relationship.