fix: Avoid write empty state

[joaopamaral]

Summary

Currently, Meltano sends an empty state message when no state is provided in the --state parameter. The issue arises when the state message is processed and the database is updated. If the Meltano extraction fails before the next state message is sent, the state in the database will be empty, leading to the loss of the last known state.

2025-01-28T18:32:50.566137Z [debug    ] {"type":"STATE","value":{}}    cmd_type=extractor name=tap-zendesk (out)

This issue has been observed across several extractors using PostgreSQL on Cloud SQL (GCP) as the Meltano database, forcing manual updates to restore the state.

Bug Fixes:

• Avoid writing empty state messages when the state is empty.

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📚 Documentation preview 📚: https://meltano-sdk--2844.org.readthedocs.build/en/2844/

Summary by Sourcery

Bug Fixes:

• Prevent writing empty state messages to the database if the state is empty.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request prevents the writing of empty state messages, which could lead to data loss. The changes ensure that state messages are only written if the state is not empty, or if the current state is different from the last emitted state.

Sequence diagram for state message handling in Meltano

sequenceDiagram
    participant Extractor
    participant StateHandler
    participant Database

    Note over Extractor,Database: Before Fix
    Extractor->>StateHandler: Start extraction
    StateHandler->>Database: Write empty state {}
    Note right of Database: State is lost if extraction fails

    Note over Extractor,Database: After Fix
    Extractor->>StateHandler: Start extraction
    alt State is not empty
        StateHandler->>Database: Write state message
    else State is empty
        Note over StateHandler: Skip writing empty state
    end

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State diagram for state message handling logic

stateDiagram-v2
    [*] --> CheckState
    CheckState --> EvaluateConditions: State exists
    CheckState --> [*]: Empty state

    EvaluateConditions --> WriteState: State not flushed AND
State different from last
    EvaluateConditions --> [*]: Conditions not met

    WriteState --> UpdateLastEmitted: Write state message
    UpdateLastEmitted --> [*]: Copy state

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File-Level Changes

Change	Details	Files
Avoid writing empty state messages.	Modified the _write_state_message method in singer_sdk/streams/core.py to check if the state is not empty before writing a state message. Modified the sync_all method in singer_sdk/tap_base.py to check if the state is not empty before writing a state message.	singer_sdk/streams/core.py singer_sdk/tap_base.py
Updated tests to reflect changes in state message emission.	Adjusted assertions in tests/core/test_parent_child.py to account for the change in the order of messages. Added initial state to the SQLiteTap in tests/samples/test_target_sqlite.py. Adjusted the expected number of state messages in tests/samples/test_tap_countries.py.	tests/core/test_parent_child.py tests/samples/test_target_sqlite.py tests/samples/test_tap_countries.py

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.33%. Comparing base (6ed507e) to head (b713e23).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2844   +/-   ##
=======================================
  Coverage   91.33%   91.33%           
=======================================
  Files          62       62           
  Lines        5205     5206    +1     
  Branches      671      672    +1     
=======================================
+ Hits         4754     4755    +1     
  Misses        319      319           
  Partials      132      132           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[codspeed-hq]

CodSpeed Performance Report

Merging #2844 will not alter performance

_{Comparing joaopamaral:fix/avoid-write-empty-state (b713e23) with main (6ed507e)}

Summary

✅ 7 untouched benchmarks

[edgarrmondragon]

Hey @joaopamaral, any particular reason for closing this?

[joaopamaral]

Hey @joaopamaral, any particular reason for closing this?

Hi @edgarrmondragon, I'll finish adding the test cases before reopen it! Maybe I should just open as draft 😅

[joaopamaral]

This test was incorrect before because the state was not included in the provided state to the second call.

  - {"type":"STATE","value":{}}
  + {"type":"STATE","value":{"bookmarks":{"main-t0":{"replication_key":"c1","replication_key_value":55}}}}

[sourcery-ai]

Hey @joaopamaral - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[edgarrmondragon]

(Doing some manual testing to ensure we don't regress on #1750 / #1753, and then see if I can add unit tests here for that)

[edgarrmondragon]

(Doing some manual testing to ensure we don't regress on #1750 / #1753, and then see if I can add unit tests here for that)

Ok, I've confirmed that the initial state message is emitted if --state ... is passed and the state is not empty.

[edgarrmondragon]

Thank you @joaopamaral!