如何使用 postgres 在 peewee 查询中访问 ArrayField 的最后一个索引？

Question

I have a model with an Array field, and I'd like to find records where the last element of the field is greater than a known value. The array field will hold arrays of varying length.

I thought that using something like Test.select().where(known_value <= Test.array_field[-1]) for model {Test} would work, but that {-1} doesn't seem to work as expected. Here's a minimum working example:

from os import path, environ

import peewee as pw
from playhouse.postgres_ext import ArrayField

from db_stuff import connect, get_database

class Test(pw.Model):
    # note an 'id' primary key field will be created by peewee by default
    value = ArrayField(pw.IntegerField)
    class Meta:
        table_name = 'test2'

# connects the model to the database and returns the instance, details are
# unimportant
connect('test_db_login.json', [Test])
database = get_database()  

database.create_tables([Test])

Test.create(value=[1,2,3,4])
Test.create(value=[5,6,7,8])

known_value = 6

for entry in Test.select():
    # outputs both records
    print('id', entry.id, 'value', entry.value)

for entry in Test.select().where(Test.value[0] <= known_value):
    # outputs both records
    print('id', entry.id, 'value', entry.value, 'first value', entry.value[0])

for entry in Test.select().where(known_value <= Test.value[-1]):
    # outputs nothing
    print('id', entry.id, 'value', entry.value, 'last value', entry.value[-1])

When I try a raw sql query on the table, things work as expected: SELECT "t1"."id", "t1"."value" FROM "test2" AS "t1" WHERE ("t1"."value"[ARRAY_UPPER("t1"."value", 1)] >= 6); , returning the second record.

I looked around a bunch in the peewee code and searched around online for a mechanism with functionality like ARRAY_UPPER in peewee, but had no luck.

Any recommendations here?

Answer 1

You should probably index using an expression like fn.array_upper(Test.value, 1) as you indicated.

Fixed by 55ef182840f869f63 in master, will be available in the next release.