[FIX] core: add NOT NULL constraints in post-init

The method `_init_column` for the field `alias_id` of `mail.alias.mixin`
requires the reflection of models, because `mail.alias` records have a
many2one field to `ir.model`.  The actual initialization of the column
is thus performed in post-init phase (after reflection).  Therefore, the
NOT NULL constraint cannot be added right away.

X-original-commit: 2e3400f149ce4ed4c00bc49a519f58993b49bc51

odoo/fields.py

@@ -823,11 +823,15 @@ class Field(MetaField('DummyField', (object,), {})):
             # the column is new or it becomes required; initialize its values
             if model._table_has_rows():
                 model._init_column(self.name)
-                # flush values before adding NOT NULL constraint
-                model.flush([self.name])
 
         if self.required and not has_notnull:
-            model.pool.post_constraint(sql.set_not_null, model._cr, model._table, self.name)
+            # _init_column may delay computations in post-init phase
+            @model.pool.post_init
+            def add_not_null():
+                # flush values before adding NOT NULL constraint
+                model.flush([self.name])
+                model.pool.post_constraint(sql.set_not_null, model._cr, model._table, self.name)
+
         elif not self.required and has_notnull:
             sql.drop_not_null(model._cr, model._table, self.name)