How to create a flattened relationship?

From: Mike Elliott (mr..79.net)
Date: Sat Apr 24 2004 - 15:50:56 EDT

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    I've hit a brick wall in attempting to create flattened relationships
    in Cayenne. I must be doing something wrong, but from reading the
    documentation I can't see what it is. Some step or order dependency
    is assumed in the documentation but never stated.

    In order to distill the problem into as simple of a situation as
    possible, I use the Artist <-> ArtistExhibit <-> Exhibit linkage
    used as an example in the documentation. The flattened relationship
    I'm trying to achieve is to be able to obtain an array of Exhibits for
    a given Artist.

    I build an entirely new project in which to work as follows:

    mkdir ~/projects/flat

    I then run Cayenne modeler in that directory, creating a new data
    domain and data node to an existing MySql database.

    cd ~/projects/flat
    $CAYENNE_HOME/bin/modeler.sh
      File -> New Project
      Create Data Domain (name: flat-x)
      Create Data Node
         (name: flat-node,
          data source factory: org...DriverDataSourceFactory
          DB Adapter: org...MySQLAdapter
          User Name: mre
          password: secret
          Driver Class: org.gjt.mm.mysql.Driver
          Database URL: jdbc:mysql://localhost/banana)
      Create Data Map (name: flat-map)

    Then I get down to the detail work of creating the artist/exhibit
    stuff:

    In flat-map:
      Create DbEntity (DbEntity name: artist)
      Create Attribute (name: pk, type: integer, pk <y>, Mandatory <y>)
      Create Attribute
         (name: name, type: varchar, pk <n>, Mandatory <n>, Max Length 20)

      Create DbEntity (DbEntity name: exhibit)
      Create Attribute (name: pk, type: integer, pk <y>, Mandatory <y>)
      Create Attribute
         (name: name, type: varchar, pk <n>, Mandatory <n>, Max Length 40)

      Create ObjEntity
         (ObjEntity Name: Artist, Table/View: artist, Java Class: Artist)
      Create ObjEntity
         (ObjEntity Name: Exhibit, Table/View: exhibit, Java Class: Exhibit)

      Select Artist. Project -> Sync ObjEntity with DbEntity
      Select Exhibit. Project -> Sync ObjEntity with DbEntity

      Create DbEntity (DbEntity name: artist_exhibit)
      Create Attribute (name: pk, type: integer, pk <y>, Mandatory <y>)
      Create Attribute
         (name: artist_pk, type: integer, pk <n>, Mandatory <y>)
      Create Attribute
         (name: exhibit_pk, type: integer, pk <n>, Mandatory <y>)

      Create ObjEntity
         (ObjEntity Name: ArtistExhibit,
          Table/View: artist_exhibit, Java Class: ArtistExhibit)

      Select ArtistExhibit. Project -> Sync ObjEntity with DbEntity

    I feel confident that all the preceding steps are absolutely required.
    However, from this point onward, I really don't know what steps are
    required or what the order dependency is. So, I'll give it my best
    guess.

    I know I need to link the artist and exhibit tables together through
    the artist_exhibit link table, so . . .

      Select artist_exhibit DbEntity.
        Create Relationship (Name: artist_for, Target: artist)
          Database Mapping (Relationship: artist_for, Create Reverse: <y>,
                    Reverse Relationship: artist_for_x)
            Add (Source: artist_pk, Target: pk )
            Done
        Create Relationship (Name: exhibit_for, Target: exhibit)
          Database Mapping (Relationship: exhibit_for, Create Reverse: <y>,
                    Reverse Relationship: exhibit_for_x)
            Add (Source: exhibit_pk, Target: pk )
            Done

       Select ArtistExhibit ObjEntity. Project -> Sync ObjEntity with DbEntity
       Select Artist ObjEntity. Project -> Sync ObjEntity with DbEntity
       Select Exhibit ObjEntity. Project -> Sync ObjEntity with DbEntity

    Visual inspection at this point confirms that all the relationships
    have made their way into the ObjEntities. At this point, I *should*
    be able to create a flattened relationship from Artist to an array of
    Exhibits, and vice versa. Following the documentation . . .

       Select Artist ObjEntity
         Create Relationship (Name: exhibits, Target: Exhibit)
            I would click the "To Many" checkbox, but I cannot. It remains
            unchecked.
         Edit Relationship
           (Relationship: exhibits, Source: Artist, Target: Exhibit)

         At this point, I should be able to exploit the known path from Artist
         to Exhibit through ArtistExhibit. However, the DbRelationships section
         is depressingly empty.

    And there it dies. No way to create the flattened relationship. So
    . . . I must be leaving out a step, or doing things in the wrong
    order, or something, right? I have actually created a flattened
    relationship (once) before, but I don't know what extra step I
    performed, or how the order differed, or whatever it took to make the
    magic work.

    Please help. What should I be doing differently?

    Mike Elliott

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