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Mongodb changestream field filter

Skill kjuhwa/skills-hub/skills/backend/mongodb-changestream-field-filter

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Install
npx -y skills add kjuhwa/skills-hub --skill mongodb-changestream-field-filter

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Filter MongoDB change stream UPDATE events by inspecting updateDescription.updatedFields so irrelevant mutations do not trigger downstream work; INSERT/DELETE fall through as always-relevant.

SKILL.md

1.9 KB, 314 tokens by cl100k_base, as published. Nobody here has run it

MongoDB Change Stream Field Filter

Shape

Listener receives ChangeStreamDocument. For UPDATE, read updateDescription.updatedFields (a BsonDocument of dottedPath → value). Return a boolean isRelevant before handing off to the expensive processor.

Steps

  1. Register listener via Spring Data MongoDB (reactive or blocking driver).
  2. Branch on OperationType: INSERT / DELETE → always relevant.
  3. UPDATE → updatedFields = event.getUpdateDescription().getUpdatedFields().
  4. Exact check: updatedFields.containsKey("groupId").
  5. Nested/wildcard: updatedFields.keySet().stream().anyMatch(k -> k.startsWith("tags.")).
  6. Combine with OR over the "relevant fields" set; return the boolean.
  7. Not relevant → log TRACE and skip. Relevant → delegate to processor.
  8. Persist resumeToken so reconnection skips already-seen events.

Counter / Caveats

  • updatedFields is keyed by dotted path at the leaf changed. A whole-subdoc replace shows as "parent", not "parent.child" — handle both.
  • Full-document replaces ($set on root) may surface every field as "updated"; treat as relevant.
  • Never skip DELETEs on field filter — there are no fields to inspect.
  • Network hiccup / replica-set election → stream goes silent without exception; pair with mongodb-changestream-resubscribe knowledge.

What ships with it: 1 file

602 B alongside SKILL.md

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