fix: Introspection get_sequences() NotImplementedError

[shantanutomarr]

• When running migrate_schemas command that applies a migration to change the primary key field of a model from AutoField to BigAutoField, we get the following error:

NotImplementedError: subclasses of BaseDatabaseIntrospection may require a get_sequences() method

• Apparently this method is not implemented in the tenant schemas backend yet, but is expected by Django 4.2.
• This commit adds that method by refering to a pull request on the original project,
  Added get_sequences so command flush works bernardopires/django-tenant-schemas#567.
• This enhancement is particularly beneficial for operations like migrations and data integrity checks, ensuring that sequence-related functionalities operate correctly within the multi-tenant architecture.

[coderabbitai]

Walkthrough

The pull request adds a new SQL query and a method to the DatabaseSchemaIntrospection class. The introduced _get_sequences_query obtains sequence names and associated column names for a given table and schema by joining PostgreSQL system catalog tables. The new get_sequences method executes this query using a cursor, processes the results into a list of dictionaries, and returns the sequence information for the specified table. No existing functionality is modified.

Changes

File	Summary of Changes
tenant_schemas/.../introspection.py	Added _get_sequences_query and a new method get_sequences(cursor, table_name, table_fields=()) to retrieve sequence metadata

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant Introspection
    participant DB

    Client->>Introspection: Call get_sequences(cursor, table_name)
    Introspection->>Introspection: Build _get_sequences_query
    Introspection->>DB: Execute query via cursor
    DB-->>Introspection: Return sequence metadata
    Introspection-->>Client: Return list of sequence dictionaries

Loading

Poem

I'm a rabbit in the code forest, so spry,
Hopping on sequences that gracefully fly,
A new query crafted in SQL art,
Fetching details that set data apart,
With each jump, my schema sings its tune,
Celebrating changes under a digital moon.

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Reviewing files that changed from the base of the PR and between a77655c and 9f7beb1.

📒 Files selected for processing (1)

• tenant_schemas/postgresql_backend/introspection.py (2 hunks)

🔇 Additional comments (2)

tenant_schemas/postgresql_backend/introspection.py (2)

177-190: Well-constructed SQL query for PostgreSQL sequence introspection

The SQL query is appropriately designed to retrieve sequence information by joining the necessary PostgreSQL system catalog tables. It correctly filters for sequences (s.relkind = 'S') with appropriate dependency types (d.deptype in ('a', 'n')) in the given schema and table.

This query handles the PostgreSQL-specific aspects of identifying sequences associated with columns in a table, which is essential for Django 4.2's migration operations.

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334-343: Correctly implements the required Django interface for sequence introspection

This implementation correctly follows Django's expected interface for the get_sequences method, which is required by Django 4.2 when working with AutoField to BigAutoField migrations. The method:

1. Properly executes the SQL query with the correct parameters
2. Returns sequences in the expected format (list of dictionaries with name, table, and column keys)
3. Maintains consistency with Django's introspection API

This addition will resolve the NotImplementedError mentioned in the PR description and enable proper schema migrations with Django 4.2.

✨ Finishing Touches

• 📝 Generate Docstrings

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