[IMP] fields: infer required=True on related fields

One can infer related=True on a non-stored related field if all fields on the
path are related.  This cannot be done if the related field is stored: when you
create a record, the database row is created first, and the related field is
computed and stored afterwards.  Making the field required in that case would
trigger a non-null constraint violation.

openerp/fields.py

@@ -428,10 +428,12 @@ class Field(object):
 
         # determine the chain of fields, and make sure they are all set up
         recs = env[self.model_name]
+        fields = []
         for name in self.related:
             field = recs._fields[name]
             field.setup(env)
             recs = recs[name]
+            fields.append(field)
 
         self.related_field = field
 
@@ -452,6 +454,10 @@ class Field(object):
             if not getattr(self, attr):
                 setattr(self, attr, getattr(field, prop))
 
+        # special case for required: check if all fields are required
+        if not self.store and not self.required:
+            self.required = all(field.required for field in fields)
+
     def _compute_related(self, records):
         """ Compute the related field `self` on `records`. """
         # when related_sudo, bypass access rights checks when reading values