Opened 10 years ago
Closed 9 years ago
#24509 closed New feature (fixed)
Allow Expressions when saving new models
Reported by: | Alex Hill | Owned by: | |
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Component: | Database layer (models, ORM) | Version: | dev |
Severity: | Normal | Keywords: | |
Cc: | me@… | 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 (last modified by )
Opening a ticket after discussion on IRC with Josh.
You can use Expression
when updating models, but it would also be useful to be able to use them when creating models, particularly in order to apply database functions to newly-inserted values.
My specific use case for this is a PostgreSQL TSVectorField
, where instead of just inserting a value, I want to insert strip(to_tsvector(<ts_config>, unaccent(<value>)))
. Ideally, I would be able to define these all as Func
s and insert an Expression
.
I propose to fix this by making SQLInsertCompiler
check for resolve_expressions
and as_sql
, as SQLUpdateCompiler
does.
Alex
Update: patch at https://github.com/django/django/pull/5099
Change History (11)
comment:1 by , 10 years ago
Triage Stage: | Unreviewed → Accepted |
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comment:2 by , 10 years ago
Owner: | changed from | to
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Status: | new → assigned |
comment:3 by , 10 years ago
I've started to look at this but if anyone knows this part of the codebase well then I think they'd be able to add this quite quickly so feel free to re-assign this if you want to work on it
comment:4 by , 10 years ago
Owner: | removed |
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Status: | assigned → new |
comment:5 by , 10 years ago
Cc: | added |
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I also have a use-case for this - I'm trying to implement MariaDB Dynamic Columns which require calling a function to create ( https://mariadb.com/kb/en/mariadb/dynamic-columns/#column_create ).
comment:6 by , 9 years ago
Just for future reference for whoever works on this: I spent a few minutes looking at this tonight and I think that implementing this _might_ allow us to get rid of the whole Field.get_placeholder()
hook, which is effectively just a hacky way to allow fields to wrap their values in an arbitrary SQL expression at save time. (Currently only GIS fields use this hook in core.)
In the meantime, if you're wishing Django 1.8 had this feature, get_placeholder()
appears to be a usable workaround (for any given specific field type; doesn't offer generic support).
comment:7 by , 9 years ago
Description: | modified (diff) |
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Has patch: | set |
Here's my patch implementing this: https://github.com/django/django/pull/5099
It also adds support for expressions (and placeholders) in bulk inserts.
Notes:
- As Carl suggested, this should allow us to get rid of
get_placeholder()
entirely. - The handling of
AutoField
s is a bit ugly at the moment. If anAutoField
's value isNone
, it's removed from the list of fields inModel._save_table()
and then conditionally re-added inSQLInsertCompiler.as_sql()
. I'm thinking about nicer ways to handle this. - There is a heap of same-but-different code between
SQLInsertCompiler
andSQLUpdateCompiler
, especially now that expressions are supported. I'd like to clean this up in a subsequent patch. - I've changed the workaround for #10888. I'm pretty sure it won't change anything, but I can't test in Oracle.
comment:8 by , 9 years ago
Needs documentation: | set |
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Patch needs improvement: | set |
comment:9 by , 9 years ago
Needs documentation: | unset |
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Patch needs improvement: | unset |
https://github.com/django/django/pull/5324 is a docs update + rebase. Ready for better review. I haven't reviewed close enough to say whether or not this should make 1.9 though. If other ORM people are around, please feel free to comment. I'm hoping to get an hour later to properly go over this.
comment:10 by , 9 years ago
Triage Stage: | Accepted → Ready for checkin |
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Sounds like a good idea to me. This will also be one step towards database based default values which could be a nice feature.