QGIS » QGIS Application

The case is pretty subtle:

- create two tables named "Child" and "Parent" with UUID Primary keys
- add a Foreign key in "Child" table pointing to the parent ID (allowing null values)
- In QGIS, add the same relation and use a reference relation widget for the FK field.
- Check the "Allow Null" box
- watch pg logs
- activate transaction groups
- create a child feature, and DO NOT create or affect any parent related feature. Validate.
- use identify tool to open the child feature form again

This triggers a syntax error in QGIS when QGIS tries to populate the new form with parent features values.

QGIS opens a cursor to fetch values with a (translated) error:

DECLARE qgis_235 BINARY CURSOR WITH HOLD FOR SELECT st_asbinary("geometrie",'NDR'),"id"::text, ...field list here ... FROM "public"."parent" WHERE ("id" = 'NULL')
Result: 7 (ERROR:  invalid syntax for uuid : « NULL »

In fact this should be converted to ` "id" is NULL ` to avoid that.

unchecking the box solves the issue. (Which makes me wonder what is the use of that checkbox)

This DDL script can help reproducing the issue.

create table parent
(
  id uuid NOT NULL, -- Identifiant unique. Lien vers la table ouvrepere
  comment character varying, -- Commentaire sur la sécurité du personnel 
  geom geometry(LineString,2154),
  CONSTRAINT parent_pkey PRIMARY KEY (id)
)
WITH (
  OIDS=FALSE
);

create table child_geo
(
  id uuid NOT NULL, 
  comment character varying,
 fk_parent uuid, -- parent fk id 
  geom geometry(Point, 2154),
  CONSTRAINT child_geo_pkey PRIMARY KEY (id),
  CONSTRAINT child_geo_parent_fk FOREIGN KEY (fk_parent)
      REFERENCES public.parent(id) MATCH SIMPLE
      ON UPDATE SET NULL ON DELETE SET NULL

)
WITH (
  OIDS=FALSE
);