#29049 closed New feature (fixed)
Add slicing notation to F expressions
Reported by: | Matthew Pava | Owned by: | Nick Pope |
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Component: | Database layer (models, ORM) | Version: | dev |
Severity: | Normal | Keywords: | slice F |
Cc: | Adam Johnson, josh.smeaton@… | Triage Stage: | Ready for checkin |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
For fields that are string expressions, the slicing notation should utilize database functions Substr
, Left
, and Right
. Those functions could even be deprecated to require the use of slicing notation.
For fields that are iterable expressions, such as ArrayField
s or HStoreField
s, those could utilize slicing notation in a Pythonic manner.
Change History (28)
comment:1 by , 7 years ago
comment:2 by , 7 years ago
I think this is a reference to my post on the developers mailing list.
That would be F('textfield')[0:5]
which would map to SubStr
and F('arrayfield')[0:10]
which would map to PostgreSQL arrayfield[1:10]
.
comment:3 by , 7 years ago
Triage Stage: | Unreviewed → Accepted |
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comment:4 by , 7 years ago
Cc: | added |
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comment:5 by , 7 years ago
Needs documentation: | set |
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Needs tests: | set |
Owner: | changed from | to
Status: | new → assigned |
comment:6 by , 7 years ago
Cc: | added |
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comment:8 by , 7 years ago
Needs documentation: | unset |
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Needs tests: | unset |
comment:10 by , 6 years ago
Owner: | changed from | to
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Taking over this since the current asignee hasn't worked on it in a while.
comment:11 by , 6 years ago
Patch needs improvement: | unset |
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comment:12 by , 5 years ago
Needs tests: | set |
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Patch needs improvement: | set |
comment:13 by , 4 years ago
Cc: | added |
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comment:14 by , 4 years ago
Owner: | removed |
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Status: | assigned → new |
Since feedback on the review came 10 months after I submitted the patch, and it now has been more than a year since it was submitted, it would be too much of an effort for me to put my mind into this again and get it into a mergable state.
comment:15 by , 4 years ago
Owner: | set to |
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Status: | new → assigned |
comment:16 by , 3 years ago
Owner: | changed from | to
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comment:17 by , 3 years ago
Cc: | removed |
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comment:18 by , 3 years ago
Needs tests: | unset |
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Patch needs improvement: | unset |
comment:19 by , 3 years ago
Needs tests: | set |
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Patch needs improvement: | set |
comment:20 by , 3 years ago
Needs tests: | unset |
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comment:21 by , 2 years ago
Owner: | changed from | to
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comment:22 by , 2 years ago
I have been reading up about this issue to continue and finish it off from where David left it, and I have some doubts. The SQL query left by Felix in this comment also doesn't generate any QuerySet or objects. I tried to run that query using Manager.raw()
, which generated no results.
Further I investigated the resolve_expression
method of SliceableF
class in django/db/models/expressions.py
, and compared it to other implementations of resolve_expression method in other classes but couldn't find anything concrete which might point to where the error might be.
Does a special method for handling slicing and indexing for OuterRef query need to be written so it is properly resolved? That is what I'm thinking because I can't find anything else that is properly handling slicing for OuterRef Queries, unless I'm missing something.
Also should None
be used instead of ''
in slice_expression for end if length is not provided?
comment:24 by , 2 years ago
Patch needs improvement: | set |
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comment:25 by , 13 months ago
Owner: | changed from | to
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Patch needs improvement: | unset |
New PR with some fixes. Hopefully we can finally get this over the line...
comment:26 by , 12 months ago
Triage Stage: | Accepted → Ready for checkin |
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Could you give an example of what the syntax would look like?