The SQLite3 adapter now implements the supports_deferrable_constraints? contract

[fractaledmind]

Motivation / Background

SQLite is a feature-rich database engine, and production usage is only growing. We need Rails' support to offer developers the range and scope of its features.

The PostgreSQL adapter supports deferred foreign keys, and SQLite itself has support deferred foreign keys since at least 2011.

Detail

Implementing the full supports_deferrable_constraints? contract allows foreign keys to be deferred by adding the :deferrable key to the foreign_key options in the add_reference and add_foreign_key methods.

add_reference :person, :alias, foreign_key: { deferrable: :deferred }
add_reference :alias, :person, foreign_key: { deferrable: :deferred }

In this PR, I am adding full support for the SQLite3Adapter by implementing:

ActiveRecord::ConnectionAdapters::SQLite3::SchemaCreation#visit_AddForeignKey
ActiveRecord::ConnectionAdapters::SQLite3::SchemaCreation#visit_ForeignKeyDefinition
ActiveRecord::ConnectionAdapters::SQLite3Adapter#supports_deferrable_constraints?
ActiveRecord::ConnectionAdapters::SQLite3::SchemaStatements#assert_valid_deferrable

and altering:

ActiveRecord::ConnectionAdapters::SQLite3::SchemaStatements#add_foreign_key
ActiveRecord::ConnectionAdapters::SQLite3Adapter#foreign_keys

Additional Info

In order to get the ActiveRecord::ConnectionAdapters::SQLite3Adapter#foreign_keys method working properly, I had to add a query to get the CREATE TABLE sql and parse which foreign key constraints are deferrable and which of those are deferred. In order to support this use-case, I extracted a table_structure_sql method which now table_structure_with_collation relies on.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[fractaledmind]

Could the test failure be a flaky test? I can't reproduce locally and the error (SQLite3::IOException: disk I/O error) is a reflection of an OS-level problem:

his is what SQLite returns when it gets a hardware error while trying to do something.
— https://sqlite.org/forum/info/f0740edfea56d61b733d83e469a55436df66f34defb219ff806dccceb0e086eb

Could we retry the build?

[zzak]

Could the test failure be a flaky test? I can't reproduce locally and the error (SQLite3::IOException: disk I/O error) is a reflection of an OS-level problem:

Could we retry the build?

I've issued a rebuild. 🙏

Edit: The rebuild failed, but this test is also flaking on main.

[fractaledmind]

@zzak the fix for this flaky test is in main, can we rebuild this PR?

[zzak]

@fractaledmind Could you rebase please? 🙇

[yahonda]

Would you address the activerecord/CHANGELOG.md conflict?

[fractaledmind]

@yahonda: Done (for both of my PRs)

[yahonda]

Rails main branch version is already 7.2.0.alpha, I'd like to keep this deprecation message as the PostgreSQL adapter does.

rails/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

Lines 526 to 528 in 2a986b7

	ActiveRecord.deprecator.warn(<<~MSG)
	`deferrable: true` is deprecated in favor of `deferrable: :immediate`, and will be removed in Rails 7.2.
	MSG