Joining with no ON condition and no FK.

(Postgres 10 and peewee version 3.7.0)

To make this simple to test, I’ve assembled some ready to use SQL:

create table table1(
  id serial primary key
);

create table table2(
  id serial primary key
);

create table table3(
  id serial primary key,
  table1_id int,
  table2_id int
);

insert into table1 (id) values (1), (2), (3);
insert into table2 (id) values (1), (2);
insert into table3 (id, table1_id, table2_id) values (1, 1, 1), (2, 1, 2), (3, 2, 1);

I want to execute the following query, using Peewee:

SELECT t1.id, t2.id, t3.id
FROM table1 t1
CROSS JOIN table2 t2
LEFT JOIN table3 t3
on t3.table1_id = t1.id and t3.table2_id = t2.id
where t3.id is null;

Note the CROSS JOIN with no “on” condition.

I’ve tried the following:

results = (table1.select(table1.id.alias("table1_id"), table2.id.alias("table2_id"), table3.id.alias("table3_id"))
                   .join(table2, JOIN.CROSS)
                   .join(table3, JOIN.LEFT_OUTER, on=((table3.table1_id == table1.id) & (table3.table2_id == table2.id)))
                   .where(table3.id.is_null()))

This is returning ValueError: Unable to find foreign key between <Model: Table1> and <Model: Table2>. Please specify an explicit join condition.

I’ve also tried replacing the CROSS JOIN with some raw sql (helps in many other edge cases with peewee): .join(SQL("CROSS JOIN table2"))

This is in turn returning UnboundLocalError: local variable 'constructor' referenced before assignment

Is there any way to get this query to work?

[coleifer]

Working up a fix.

[joaodlf]

No worries. You’re an absolute star for getting on this so quickly!