:sparkles: add table creation order computation with FK constraints

[techouse]

This pull request introduces enhancements to the MySQL-to-SQLite data transfer process, focusing on foreign key handling, schema metadata extraction, and table creation order computation. Additionally, unit tests have been expanded to ensure robust functionality and edge case coverage.

Enhancements to MySQL-to-SQLite data transfer:

• Foreign key handling during transfer:

  • Added computation of table creation order to respect foreign key constraints using the new compute_creation_order function. Tables are processed in a dependency-safe order, and cyclic dependencies are logged as warnings.
  • Implemented a post-transfer check for foreign key constraint violations in SQLite using PRAGMA foreign_key_check. Violations are logged for debugging purposes.

• Schema metadata extraction:

  • Introduced the fetch_schema_metadata function to retrieve table names and foreign key relationships from the MySQL schema. This ensures robust handling of various row formats and edge cases.

Codebase improvements:

• Topological sorting for table creation:
  • Added the topo_sort_tables function to perform topological sorting of tables based on foreign key dependencies. This ensures tables are created in a foreign key-safe order. Cyclic dependencies are identified and returned for further analysis.

Unit test enhancements:

• Expanded test coverage for new functionality:
  • Added tests for topo_sort_tables to verify behavior with acyclic, cyclic, and empty dependency graphs.
  • Added tests for fetch_schema_metadata to ensure robust handling of diverse row formats, including tuples, lists, objects, dictionaries, and invalid types.
  • Added tests for compute_creation_order to validate table ordering and cycle detection in schemas with and without circular dependencies.
  • Enhanced transfer method tests to verify foreign key checks and exception handling during SQLite operations.

[coderabbitai[bot]]

Walkthrough

New utilities for extracting MySQL schema metadata and determining table creation order respecting foreign key constraints were introduced. The transfer method in the transporter now uses this order, logs cycles, and checks for foreign key violations after transfer. Comprehensive unit tests were added for both the utility functions and the updated transfer logic.

Changes

File(s)	Change Summary
src/mysql_to_sqlite3/mysql_utils.py	Added functions: fetch_schema_metadata, topo_sort_tables, and compute_creation_order for FK-aware ordering.
src/mysql_to_sqlite3/transporter.py	Modified transfer method to use FK-aware table order, handle cycles, and check FK constraints post-transfer.
tests/unit/test_mysql_utils.py	Added tests for topological sorting, schema metadata extraction, and creation order computation.
tests/unit/test_transporter.py	Enhanced and added tests for transfer logic, table ordering, cycle handling, and FK constraint checks.

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant MySQLtoSQLite
    participant MySQLConn
    participant SQLiteConn

    User->>MySQLtoSQLite: transfer()
    MySQLtoSQLite->>MySQLConn: fetch_schema_metadata()
    MySQLConn-->>MySQLtoSQLite: tables, FK edges
    MySQLtoSQLite->>MySQLtoSQLite: topo_sort_tables()
    alt Cyclic dependencies detected
        MySQLtoSQLite->>MySQLtoSQLite: Log warning
    end
    MySQLtoSQLite->>SQLiteConn: PRAGMA foreign_keys=OFF
    loop For each table in order
        MySQLtoSQLite->>SQLiteConn: Transfer table data
    end
    MySQLtoSQLite->>SQLiteConn: PRAGMA foreign_keys=ON
    MySQLtoSQLite->>SQLiteConn: PRAGMA foreign_key_check
    SQLiteConn-->>MySQLtoSQLite: FK violations (if any)
    MySQLtoSQLite->>MySQLtoSQLite: Log FK violations

Suggested labels

mariadb

Poem

In the warren of tables, dependencies entwine,
Now sorted with care, in a foreign-key line.
If cycles appear, a warning will sound,
And after the hop, constraint checks abound.
With tests all a-flutter, our code’s in fine shape—
A database journey, with nary escape!
🐇✨

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.66667% with 7 lines in your changes missing coverage. Please review.

Project coverage is 94.11%. Comparing base (ab601c3) to head (de6cff2).

Files with missing lines	Patch %	Lines
src/mysql_to_sqlite3/mysql_utils.py	88.67%	6 Missing :warning:
src/mysql_to_sqlite3/transporter.py	95.45%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   94.40%   94.11%   -0.29%     
==========================================
  Files           8        8              
  Lines         643      714      +71     
==========================================
+ Hits          607      672      +65     
- Misses         36       42       +6     

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[techouse]

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