[IMP] fields: relational fields automatically behave as mapped

In other words, `recs.foo_id == recs.mapped('foo_id')`.

odoo/addons/base/tests/test_api.py

@@ -491,11 +491,13 @@ class TestAPI(common.TransactionCase):
         """ Check map on recordsets. """
         ps = self.env['res.partner'].search([])
         parents = ps.browse()
-        for p in ps: parents |= p.parent_id
+        for p in ps:
+            parents |= p.parent_id
 
         # map a single field
         self.assertEqual(ps.mapped(lambda p: p.parent_id), parents)
         self.assertEqual(ps.mapped('parent_id'), parents)
+        self.assertEqual(ps.parent_id, parents)
 
         # map a sequence of fields
         self.assertEqual(
@@ -506,6 +508,10 @@ class TestAPI(common.TransactionCase):
             ps.mapped('parent_id.name'),
             [p.name for p in parents]
         )
+        self.assertEqual(
+            ps.parent_id.mapped('name'),
+            [p.name for p in parents]
+        )
 
         # map an empty sequence of fields
         self.assertEqual(ps.mapped(''), ps)

odoo/fields.py

@@ -989,7 +989,7 @@ class Field(MetaField('DummyField', (object,), {})):
         if record is None:
             return self         # the field is accessed through the owner class
 
-        if record:
+        if record._ids:
             # only a single record may be accessed
             record.ensure_one()
             try:
@@ -2033,6 +2033,15 @@ class _Relational(Field):
         'context': {},                  # context for searching values
     }
 
+    def __get__(self, records, owner):
+        # base case: do the regular access
+        if records is None or len(records._ids) <= 1:
+            return super().__get__(records, owner)
+        # multirecord case: return the union of the values of 'self' on records
+        get = super().__get__
+        comodel = records.env[self.comodel_name]
+        return comodel.union(*[get(record, owner) for record in records])
+
     def _setup_regular_base(self, model):
         super(_Relational, self)._setup_regular_base(model)
         if self.comodel_name not in model.pool: