Peewee：如何从Postgres中选择数组字段为空的数据？

Question

Here is a simple Peewee model to work with Postgres

import playhouse.postgres_ext as pg


db = pg.PostgresqlDatabase(""" credentials ... """)


class Artist(pg.Model):
   name = pg.TextField()
   albums = pg.ArrayField(pg.TextField, default=[])

   class Meta:
      database = db


db.create_table(Artist)
Artist.create(name='name1', albums=['album11', 'album12'])
Artist.create(name='name2')

For selecting artists with no albums the SQL query may be

>> SELECT * FROM artist WHERE albums = '{}';

 id | name  | albums 
----+-------+--------
  2 | name2 | {}

or for selecting artists with specific name

>> SELECT * FROM artist WHERE name = 'name1';

 id | name  |      albums       
----+-------+-------------------
  1 | name1 | {album11,album12}

But when I try to achieve it with Peewee I get the following results

res = Artist.select().where(Artist.name == 'name1')
assert len(res) == 1 and res[0].name == 'name1'

res = Artist.select().where(Artist.albums == '{}')
assert len(res) == 0

The first query takes 'name1' as query parameter.

The second query takes playhouse.postgres_ext._Array object as query parameter.

I've looked at documentation on Postgres Extensions and did not find anything suitable.

Could someone explain what am I doing wrong and how to select data with empty array field?

Answer 1

You can drop into raw SQL to work around this limitation:

res = Artist.select().where(SQL("albums = '{}'"))
print(len(res))