[Django] #29168: Custom lookup documentation is incomplete

[Django]

#29168: Custom lookup documentation is incomplete
-------------------------------------+-------------------------------------
Reporter: jjwatt99 | Owner: nobody
Type: Bug | Status: new
Component: Database | Version: 2.0
layer (models, ORM) |
Severity: Normal | Keywords: lookup
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
The page for creating custom field lookups is incomplete. I am referring
to the doc at https://docs.djangoproject.com/en/2.0/howto/custom-lookups/.
The documentation is unclear about how to use the left-hand side value
(lhs) and right-hand side value (rhs) properly. For example, lets say you
have a lookup like
{{{
id__custom='abc123'
}}}
The lhs is the ID field and the rhs is the 'abc123'. I want to create a
query like
{{{
WHERE 'abc123' LIKE id||%
}}}
However the documentation is unclear about how to reference the lhs in the
as_sql method. Users would like to know how to reference the rhs BEFORE
the LIKE and the lhs AFTER the LIKE in the sql query above. The
documentation only shows examples where the lhs comes first and the rhs
last. This would help users create a custom lookup with the sql above.

--
Ticket URL: <https://code.djangoproject.com/ticket/29168>
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[Django]

#29168: Document how to write a custom lookup where the rhs comes before the lhs
-------------------------------------+-------------------------------------
Reporter: JJ Gutierrez | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database layer | Version: 2.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: lookup | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by Tim Graham):

* type: Bug => Cleanup/optimization
* stage: Unreviewed => Accepted

Comment:

Maybe looking at
[https://github.com/django/django/blob/master/django/db/models/lookups.py
the built in lookups] would offer a hint.

--
Ticket URL: <https://code.djangoproject.com/ticket/29168#comment:1>

[Django]

#29168: Document how to write a custom lookup where the rhs comes before the lhs

--------------------------------------+------------------------------------

Reporter: JJ Gutierrez | Owner: nobody

Type: Cleanup/optimization | Status: new
Component: Documentation | Version: 2.0

Severity: Normal | Resolution:
Keywords: lookup | Triage Stage: Accepted

Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0

--------------------------------------+------------------------------------
Changes (by Tim Graham):

* component: Database layer (models, ORM) => Documentation

--
Ticket URL: <https://code.djangoproject.com/ticket/29168#comment:2>

[Django]

#29168: Document how to write a custom lookup where the rhs comes before the lhs
--------------------------------------+------------------------------------

Reporter: JJ Gutierrez | Owner: samermi1
Type: Cleanup/optimization | Status: assigned

Component: Documentation | Version: 2.0
Severity: Normal | Resolution:
Keywords: lookup | Triage Stage: Accepted

Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0

--------------------------------------+------------------------------------
Changes (by samermi1):

* status: new => assigned
* owner: nobody => samermi1

Comment:

I will try to fix this one

--
Ticket URL: <https://code.djangoproject.com/ticket/29168#comment:3>

[Django]

#29168: Document how to write a custom lookup where the rhs comes before the lhs

-------------------------------------+-------------------------------------

Reporter: JJ Gutierrez | Owner: nobody

Type: | Status: closed
Cleanup/optimization |
Component: Documentation | Version: 2.0
Severity: Normal | Resolution: invalid
Keywords: lookup | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by Mariusz Felisiak):

* status: new => closed
* resolution: => invalid
* stage: Accepted => Unreviewed

Comment:

> However the documentation is unclear about how to reference the lhs in
the as_sql method. Users would like to know how to reference the rhs
BEFORE the LIKE and the lhs AFTER the LIKE in the sql query above. The
documentation only shows examples where the lhs comes first and the rhs
last. This would help users create a custom lookup with the sql above.

IMO [https://docs.djangoproject.com/en/dev/howto/custom-lookups/#a-lookup-
example "A lookup example"] makes it really clear, I don't see how we
could make it clearer. You need to swap `lhs` and `rhs`, e.g.:
{{{
class Custom(Lookup):
lookup_name = 'custom'

def as_sql(self, compiler, connection):
lhs, lhs_params = self.process_lhs(compiler, connection)
rhs, rhs_params = self.process_rhs(compiler, connection)
params = rhs_params + lhs_params
return '%s LIKE %s||%%' % (rhs, lhs), params
}}}

Closing as invalid.

--
Ticket URL: <https://code.djangoproject.com/ticket/29168#comment:3>