The foreign_keys table provides information
        about foreign keys on NDB tables. This table
        has the following columns:
- object_id- The foreign key's object ID 
- name- Name of the foreign key 
- parent_table- The name of the foreign key's parent table 
- parent_columns- A comma-delimited list of parent columns 
- child_table- The name of the child table 
- child_columns- A comma-separated list of child columns 
- parent_index- Name of the parent index 
- child_index- Name of the child index 
- on_update_action- The - ON UPDATEaction specified for the foreign key; one of- No Action,- Restrict,- Cascade,- Set Null, or- Set Default
- on_delete_action- The - ON DELETEaction specified for the foreign key; one of- No Action,- Restrict,- Cascade,- Set Null, or- Set Default