Index strings

[mmathieum]

• Index strings parser#19
• Index strings commons-android#41

Links:

• https://blog.transitapp.com/how-we-shrank-our-trip-planner-till-it-didnt-need-data-84984ca56663/

[mmathieum]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces functionality to index strings, likely for optimization, by adding a new strings table and related definitions. The changes are a good step towards improving performance.

My review has identified a few areas for improvement:

• The new strings table's primary key definition can be improved to ensure it's an auto-incrementing primary key, which is crucial for data integrity.
• The INSERT statement for the new table needs to be adjusted accordingly.
• A minor copy-paste error was found in a region comment.
• An unused constant with an unconventional name has been added.

I've provided specific suggestions to address these points.

[Copilot]

Pull request overview

This PR introduces string indexing functionality to optimize database storage by replacing repeated string values with indexed references. The implementation follows the approach described in the linked Transit blog post about reducing data size.

Key changes:

• Adds utility extension functions for unescaping SQL strings
• Creates a new strings table schema to store unique strings with auto-generated IDs
• Defines column index arrays to identify which table columns should use string indexing
• Adds a feature flag to control the export of indexed strings

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/main/java/org/mtransit/commons/sql/SQLUtils.kt	Adds extension functions for unquoting and unescaping SQL strings
src/main/java/org/mtransit/commons/GTFSCommons.kt	Defines string indexing schema, column mappings for route/direction/stop tables, and separator constant
src/main/java/org/mtransit/commons/FeatureFlags.kt	Adds feature flag to enable/disable string export functionality

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