#34955: Make available the string concatenation operator `||` for PostgreSQL
-------------------------------------+-------------------------------------
Reporter: Paolo Melchiorre | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: field, database, | Triage Stage:
generated, output_field | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Paolo Melchiorre):
Replying to [comment:8 Mariusz Felisiak]:
> If casting to text data-type fixes the issue then I'd consider
documenting this workaround instead of adding a PostgreSQL-specific
function (where text casting would still be required). For example, adding
the following sentence:
>
> ''"In order to make an `IMMUTABLE` expression `MUTABLE` on PostgreSQL,
you can wrap the expression with `Cast()`, e.g.
`Cast(Concat(F("first_name"), Value(" "), F("last_name")),
TextField())`."''
>
> in the warning about `IMMUTABLE` functions on PostgreSQL.
Unfortunately the SQL code generate by the Django ORM is still broken in
PostgreSQL.
I wrote the class as susggested by Mariusz:
{{{
#!python
class Person(models.Model):
first_name = models.CharField()
last_name = models.CharField()
full_name = models.GeneratedField(
expression=Cast(
Concat("first_name", V(" "), "last_name"),
models.TextField(),
),
db_persist=True,
output_field=models.TextField(),
)
}}}
But the migrations generate this SQL code:
{{{
#!sql
CREATE TABLE "samples_person" (
"id" bigint NOT NULL PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
"first_name" varchar NOT NULL,
"last_name" varchar NOT NULL,
"full_name" text GENERATED ALWAYS AS (
(
CONCAT(
("first_name")::text,
(CONCAT((' ')::text, ("last_name")::text))::text
)
)::text
) STORED
);
}}}
that generated this error message `psycopg.errors.InvalidObjectDefinition:
generation expression is not immutable`
--
Ticket URL: <https://code.djangoproject.com/ticket/34955#comment:9>
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