OK. descriptions of tables are below.

Both Users and Sessions are referenced by Sessions_Metadata

Class::DBI doc says has_many is used to declare that another table is referencing us, so both Users and Sessions need a has_many(sessions_metadata)?

I tried this in sessions:

__PACKAGE__->has_many(
                      sessions_metadata=>['EP::Common::DBI::Sessions_M
+etadata' => 'session_id' ]
                      => 'id'
);
[download]

(and equiv in users) which I was hoping meant that 'session_id' is an FK in Sessions_Metadata which refers to 'id': the PK in sessions.
Still get the same error.
have I got the wrong end of the stick?

sessions_metadata
   Column    |          Type          | Modifiers 
-------------+------------------------+-----------
 session_id  | character(32)          | not null
 username    | character varying(40)  | 
 create_date | character varying(100) | 
 expire      | character varying(100) | 
 query_id    | character varying(50)  | 
Indexes: sessions_metadata_pkey primary key btree (session_id)
Foreign Key constraints: $1 FOREIGN KEY (session_id) REFERENCES sessio
+ns(id) ON UPDATE NO ACTION ON DELETE NO ACTION,
                         $2 FOREIGN KEY (username) REFERENCES users(us
+ername) ON UPDATE NO ACTION ON DELETE NO ACTION

sessions

  Column   |     Type      | Modifiers 
-----------+---------------+-----------
 id        | character(32) | not null
 a_session | text          | 
Indexes: sessions_pkey primary key btree (id)

users

    Column    |          Type          |     Modifiers      
--------------+------------------------+--------------------
 username     | character varying(40)  | not null
 password     | character varying(40)  | not null
 salt         | smallint               | not null
 session_only | smallint               | not null default 0
 first_name   | character varying(40)  | not null
 last_name    | character varying(40)  | not null
 institute    | character varying(255) | 
 department   | character varying(255) | 
 address      | character varying(255) | 
 telephone    | character varying(255) | 
 email        | character varying(100) | not null
Indexes: users_pkey primary key btree (username)
[download]