如何在Peewee的SelectQuery中实现表达式的数组切片？

Question

Is it possible to implement array slicing for Expression within SelectQuery in peewee?

I want to use pattern matching in PostgreSQL query with regexp, and I can do it with fn.REGEXP_MATCH(col_name, regexp) but it returns array as string like so "['foo']" . So I need to get only first element of array with slice on the DB side like so: (regexp_match(col_name, regexp)[1] .

I need to implement this query with orm:

SELECT (regexp_match(h.name, '^ATM-\w{5}-(\S+)$'))[1] FROM zbxhost h;

And this try returns me array as string:

ZbxHost.select(ZbxHost.name, fn.REGEXP_MATCH(ZbxHost.name, '^ATM-\w{5}-(\S+)$'))

The only thing that comes to my mind is not to use regexp. And in this case it's possible, but what if it will be necessary in future?

Answer 1

You might try using the "unnest" function (via fn.unnest).

If you're looking for implementing array-type stuff, check out the implementation of ArrayField in playhouse/postgres_ext.py:

https://github.com/coleifer/peewee/blob/b48aab31fe5cd788099b821b2c2cf5d05d196d3f/playhouse/postgres_ext.py#L114-L184