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apacheentity-relationshipapache-cayenne

Apache Cayenne 1-M relationship within same table

I am building a system that allows elements or landing spaces to be dragged onto other landing spaces. As such the model will be a tree of landing spaces with elements at the leaf.

I wish to use apache cayenne to store this data. An ideal situation would be to invoke LandingSpace.getChildren() on a cayenne "LandingSpace" class and retrieve the children, which contains landing spaces and/or elements.

Essentially I wish to make a 1-M relationship from a table to itself. Is there a way in which this can be achieved?

Many thanks

Solution

  • Sure. Relationship to self is just another relationship in Cayenne. Start with this table model:

    LANDING_SPACE
   ID        # PK
   PARENT_ID # FK to parent
   ...       # other columns

    And map a pair of relationships over the ID/PARENT_ID join: "parent" (to one) and "children" (to many)