Hello Darrel, before providing an answer, let me put some background information here.
At loading data by installing resources (models, fields, model-records, views, record rules, actions, menu entries, etc.), Odoo registers mapping records for all resources in the 'ir_model_data' table ('ir.model.data' object), so we can reference those records later, even from other modules.
Mapping records in 'ir_model_data' have the following remarkable columns:
- module: module name, string literal (not its id)
- model: fully-qualified dot-separated object name (also known as the object's technical name)
- res_id: The resource id/Database ID (the PK of the record in the table where the resource is stored)
- name: record name, a string literal that in conjunction with the module name uniquely identify the record/resource
The record name in conjunction with the module name form what we know as the resource External ID which has the following fully-qualified form: 'module_name.resource_name'.
Records defined in XML data define their External IDs by means of the 'id' attribute of the 'record' tag.
The 'id' attribute can explicitly include 'module_name.' (fully-qualified form) or not. In the later case (relative form) the module that declares the resource is assumed:
The above long story was required to have enough background for the answer that follows.
At processing child 'field' tags of any 'record' tag, the 'ref' attribute is expected to have the External ID of a referenced existing record (fully-qualified or relative form):
Mapping records that reference models are created at initializing modules/models/fields. As they lack a corresponding XML record and cannot declare its corresponding External ID by this means, the ORM creates its External ID based in the 'model_' prefix and the object's technical name (dots replaced by underscores):
This is why records that reference models ('ir.model' records) have the following form: model_XXXXX
Records for some other resources also have known prefixes for their External IDs:
- Modules: https://github.com/odoo/odoo/blob/8.0/openerp/modules/db.py#L90
- Models: https://github.com/odoo/odoo/blob/8.0/openerp/models.py#L382
- Fields: https://github.com/odoo/odoo/blob/8.0/openerp/models.py#L444
SELECT * FROM "ir_model_data" WHERE name LIKE 'module_%'; -- most are 'ir.module.module' records
SELECT * FROM "ir_model_data" WHERE name LIKE 'model_%' ORDER by module, name; -- all/most are 'ir.model' records
SELECT * FROM "ir_model_data" WHERE name LIKE 'field_%' ORDER BY module, name; -- all/most are 'ir.model.fields' records
Records for other resources may follow some convention or simply not:
SELECT * FROM "ir_model_data" WHERE name LIKE 'view_%' ORDER by module, name; -- all/most are 'ir.ui.view' records
SELECT * FROM "ir_model_data" WHERE model LIKE 'ir.ui.view' AND name NOT LIKE 'view_%' ORDER by module, name; -- 'ir.ui.view' records with unconventional names
I hope this helps you to clarify your doubts.