Add support for composite unique constraint in auto migration

[atkei]

Related to #172, #175 and based on #957.

Add UniqueConstraint to support composite unique constraint in auto migration.

from piccolo.columns import Text
from piccolo.constraint import UniqueConstraint
from piccolo.table import Table


class Band(Table):
    name = Text(required=True)
    label = Text(required=True)
    unique_name_label = UniqueConstraint(["name", "label"])

Some work remains such as adding doc and testing, but I would like to have feedback on my proposal first.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.85253% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 89.72%. Comparing base (363d683) to head (07f8b94).
Report is 1 commits behind head on master.

Files	Patch %	Lines
piccolo/apps/migrations/auto/schema_differ.py	92.85%	3 Missing ⚠️
piccolo/apps/migrations/auto/migration_manager.py	97.36%	2 Missing ⚠️
piccolo/apps/migrations/auto/diffable_table.py	95.00%	1 Missing ⚠️
piccolo/apps/migrations/auto/schema_snapshot.py	80.00%	1 Missing ⚠️
piccolo/constraint.py	96.96%	1 Missing ⚠️
piccolo/table.py	90.90%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #984      +/-   ##
==========================================
- Coverage   92.78%   89.72%   -3.07%     
==========================================
  Files         108      109       +1     
  Lines        8182     8399     +217     
==========================================
- Hits         7592     7536      -56     
- Misses        590      863     +273     

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[sinisaos]

@dantownsend I hope it's not a problem, but I have approved and run the workflow for this PR. I have already tried these changes in the @atkei local branch and in my case everything works great as I wrote in this comment. Can you try and review this PR. Thanks.

[dantownsend]

@sinisaos Awesome thanks - feel free to run the CI whenever you want.

@atkei Thanks a lot for this - looks great!

[AlexanderMakarov]

@sinisaos @dantownsend - could you make a hint - when it would be merged? Would it mean new version/release?

[dantownsend]

@AlexanderMakarov I'll try my best to review it properly this week.

[MoSheikh]

Currenty looking for this funtionality - would appreciate it someone on the team would be able to review!

[AlexanderMakarov]

@sinisaos @dantownsend - do you have some plans to deliver this functionality soon? Thank you in advance.

[sinisaos]

@AlexanderMakarov Sorry, but you have to wait for @dantownsend response.

[dantownsend]

Yes, it's definitely high on my radar. I need to try and get some improvements done to Piccolo Admin, but this is high on my list. Thanks for the patience.

[devsarvesh92]

@dantownsend Is this released?

[devsarvesh92]

@dantownsend is there any workaround to acheive this?

[sinisaos]

@devsarvesh92 For now, the workaround is to use raw sql (in migrations or script) to add a composite unique constraint, as described here.

[chilico]

@dantownsend Any advances on this getting merged & released?

[stronk7]

Hi,

great to see this coming! For sure support for composite unique indexes/constraints is a real use case!

I just wanted to introduce here a related question that is… why not make this to also support non-unique composite indexes? After all, the uniqueness is “only” an attribute of the index, isn’t it?

For sure, if in the future support for composite PKs/FKs is added, then the composite UK will need to be considered again (because FKs should be able to point to UKs too. But right now (after having read various issues here), that seems to be not trivial to happen.

So, back to the question, why not get the opportunity of this PR to, also, support non unique indexes?

Ciao :)

Disclaimer: I’m completely new to Piccolo, so maybe what I’m asking doesn’t make much sense or already can be done (apart from doing it in manual migrations), but from the research that I’m doing over various Python ORM libraries, where Piccolo is one of the “finalists”, this is pretty much, the only feature that I’m missing right now, so just sharing.

[bitliner]

when will it be merged?

[pavdwest]

Hi,

great to see this coming! For sure support for composite unique indexes/constraints is a real use case!

I just wanted to introduce here a related question that is… why not make this to also support non-unique composite indexes? After all, the uniqueness is “only” an attribute of the index, isn’t it?

For sure, if in the future support for composite PKs/FKs is added, then the composite UK will need to be considered again (because FKs should be able to point to UKs too. But right now (after having read various issues here), that seems to be not trivial to happen.

So, back to the question, why not get the opportunity of this PR to, also, support non unique indexes?

Ciao :)

Disclaimer: I’m completely new to Piccolo, so maybe what I’m asking doesn’t make much sense or already can be done (apart from doing it in manual migrations), but from the research that I’m doing over various Python ORM libraries, where Piccolo is one of the “finalists”, this is pretty much, the only feature that I’m missing right now, so just sharing.

Same here, this is the only feature I'm missing with Piccolo, so adding a friendly bump. Really enjoying this ORM so far thanks.

One question: would it be possible to reflect on the unique constraints of a model at runtime? That would be very useful, to generically handle e.g. conflicts during inserts.

[sinisaos]

@pavdwest If anyone wants to use unofficial support (until is officially supported in Piccolo) for this PR, I've made a branch in my fork that combines this PR with the reverse lookup PR. In that branch there is also support for M2M duplicate row prevention and UniqueConstraint for working with SQlite (not in migrations but when we use the create_table method). Usage is:

pip install https://github.com/sinisaos/piccolo/archive/dev.zip

As far as I was able to try everything works fine. Hope this helps until everything is officially supported in Piccolo.

[pavdwest]

@pavdwest If anyone wants to use unofficial support (until is officially supported in Piccolo) for this PR, I've made a branch in my fork that combines this PR with the reverse lookup PR. In that branch there is also support for M2M duplicate row prevention and UniqueConstraint for working with SQlite (not in migrations but when we use the create_table method). Usage is:

pip install https://github.com/sinisaos/piccolo/archive/dev.zip

As far as I was able to try everything works fine. Hope this helps until everything is officially supported in Piccolo.

Thank you very much @sinisaos, I've had a quick test of this branch::

• Tested with on_conflict as that's usually a complicated behaviour and it seems to work correctly. Nice!
• Found minor issue with using Table.create_table(if_not_exists=True) where it tries to recreate the constraint - my expectation would be that it also respects the if_not_exists param, i.e. doesn't try to create the constraint again.

Great stuff!

[sinisaos]

@pavdwest Thank you, I'm glad you find that branch useful until all that will be officially supported.

• Found minor issue with using Table.create_table(if_not_exists=True) where it tries to recreate the constraint - my expectation would be that it also respects the if_not_exists param, i.e. doesn't try to create the constraint again.

Yes, you are right, but I don't know how to solve that because of the limited support for ALTER TABLE in SQlite (for Postgres we should use migrations anyway). To prevent the SQlite OperationalError that the unique index already exists, I just commented out the unique constraint in the table definition after the first run.