fix: Update DynamicPickleType to support MySQL dialect

[hung12ct]

The process_bind_param and process_result_value methods in the DynamicPickleType class have been modified to handle MySQL dialect in addition to Spanner. This change ensures that pickled values are correctly processed for both database types.

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Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: ADK crashes with MySQL session in v1.17.0 #3283

2. Or, if no issue exists, describe the change:

If applicable, please follow the issue templates to provide as much detail as
possible.

Problem:
When using DatabaseSessionService with MySQL backend in google-adk v1.17.0, the application crashes with the following error: app.resources.runner:event_generator:260 - Error in event_generator: (builtins.TypeError) 'tuple' object cannot be interpreted as an integer

Root cause: The DynamicPickleType class in database_session_service.py configures MySQL dialect to use LONGBLOB for storing pickled data (line 117-118), but the process_bind_param and process_result_value methods only handle pickle serialization/deserialization for Spanner dialect, not MySQL. This causes MySQL to attempt storing raw Python objects instead of pickled bytes, leading to serialization errors and potential data corruption.

Solution:
Added MySQL to the pickle serialization logic in both process_bind_param and process_result_value methods, treating it the same way as Spanner dialect. This ensures that:

• Data is properly pickled to bytes before being stored in MySQL's LONGBLOB column
• Data is properly unpickled when retrieved from the database
• No breaking changes to existing functionality for other dialects (SQLite, PostgreSQL)

Testing Plan

Please describe the tests that you ran to verify your changes. This is required
for all PRs that are not small documentation or typo fixes.

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Summary of pytest results:

Manual End-to-End (E2E) Tests:

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necessary setup or configuration. Please provide logs or screenshots to help
reviewers better understand the fix.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

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[gemini-code-assist]

Summary of Changes

Hello @hung12ct, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical issue in the DynamicPickleType class within the DatabaseSessionService where it failed to properly serialize and deserialize Python objects when interacting with a MySQL backend. The fix extends the existing pickling logic, previously only applied to Spanner, to now also include MySQL. This ensures that data is correctly converted to bytes before storage in MySQL's LONGBLOB columns and then unpickled back into Python objects upon retrieval, preventing application crashes and data corruption.

Highlights

• MySQL Dialect Support: The DynamicPickleType class has been updated to correctly handle MySQL dialect for pickling and unpickling Python objects, resolving a TypeError when using DatabaseSessionService with MySQL.
• Bug Fix: This change specifically addresses a problem where MySQL was attempting to store raw Python objects instead of pickled bytes, causing serialization errors and application crashes.
• Comprehensive Unit Tests: New unit tests have been added for DynamicPickleType to verify correct behavior across MySQL, Spanner, and other dialects, including full roundtrip tests for data serialization and deserialization.

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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue where DynamicPickleType did not support the MySQL dialect, leading to crashes. The changes in database_session_service.py are simple and effective. It's great to see the addition of a comprehensive new test suite in test_dynamic_pickle_type.py to cover this new functionality and existing behavior. My feedback focuses on improving the new tests for better maintainability and readability by reducing code duplication through parameterization and using more idiomatic mock assertions.

[hung12ct]

Hi @DeanChensj, could you please help review this PR when you have a chance? Thanks a lot!

[DeanChensj]

Merged, thanks!