Fixed #29049 -- Added slicing notation to F expressions. #11208
Conversation
|
Hey @adamchainz. When you have capacity, can I ask you to look at this since you inputted on the original PR. (Thanks!) |
docs/ref/models/expressions.txt
Outdated
There was a problem hiding this comment.
I'd suggest:
However, step-argument is not supported in slicing.
changed to:
The step-argument is not supported. For example::
Also a ..versionadded annotation is needed
There was a problem hiding this comment.
Changed this to your suggestion. Added a versionadded, although I'm not sure which line to put it on?
F expressions on string-based fields and arrays can now use standard python slicing-notation. Added a new class SlicableF that handles identification of slicable fields. Step-argument is not supported. Added unit-tests and documentation, with an entry in release-notes.
Used a variable 'field_type' to avoid multiple lookups.
| * ``connection.queries`` now shows ``COPY … TO`` statements on PostgreSQL. | ||
|
|
||
| * :class:`~django.db.models.FilePathField` now accepts a callable ``path``. | ||
| * Slicing notation added to F expressions over the following field types: |
There was a problem hiding this comment.
Just nitpicking, but please add a blank line.
There was a problem hiding this comment.
Please also move this to 3.1.txt.
| normal Python assignment of value to an instance attribute, in fact it's an SQL | ||
| construct describing an operation on the database. | ||
|
|
||
| For fields that are string-expressions (or ``django.contrib.postgres.fields.ArrayField``), you can use the standard slicing |
| def slice_expression(self, expression, start, length): | ||
| if length is None: | ||
| return SliceTransform(start, 2147483647, expression) | ||
|
|
There was a problem hiding this comment.
Maybe this blank line is not needed.
| first_instance.field = F('field')[:2] | ||
| first_instance.save() | ||
| first_instance.refresh_from_db() | ||
| self.assertSequenceEqual( |
There was a problem hiding this comment.
You could collapse this to one line.
|
|
||
| def slice_expression(self, expression, start, length): | ||
| """Return a slice of an expression, or None if field is not sliceable.""" | ||
| return None |
There was a problem hiding this comment.
Default implementation should raise NotSupportedError, IMO, e.g.
raise NotSupportedError('This field does not support slicing.')also test for this error is required.
| companies = Company.objects.annotate(first_three=F('name')[:3]) | ||
| self.assertEqual(companies[0].first_three, "Exa") | ||
| self.assertEqual(companies[1].first_three, "Foo") | ||
| self.assertEqual(companies[2].first_three, "Tes") |
There was a problem hiding this comment.
You can use assertSequenceEqual().
| third_instance.refresh_from_db() | ||
| self.assertSequenceEqual( | ||
| third_instance.field, [2, 3] | ||
| ) |
|
Closing due to inactivity. |
Supersedes PRs django#9670, django#11208, django#14731, and django#16310. This adds the following changes over the previous PRs: - Used `None` to omit `end` in `ArrayField.slice_expression()` - Handled nested slicing, e.g. `F("name")[1:][:5]` - Simplified `.resolve_expression()` - Renamed `SliceableF` to `Sliced` - Clarified some inline comments Co-authored-by: Priyansh Saxena <[email protected]> Co-authored-by: Niclas Olofsson <[email protected]> Co-authored-by: David Smith <[email protected]> Co-authored-by: Mariusz Felisiak <[email protected]> Co-authored-by: Abhinav Yadav <[email protected]>
Fixed issue https://code.djangoproject.com/ticket/29049
This is a continuation on #9670