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database-mongodb

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Apply MongoDB data-modeling, indexing, and query rules from access patterns. Use when designing schemas, choosing embed vs reference, or tuning MongoDB query behavior.

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Source SKILL.md: https://github.com/HoangNguyen0403/agent-skills-standard/blob/HEAD/skills/database/database-mongodb/SKILL.md

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MongoDB Best Practices

Priority: P0 (CRITICAL)

Rules

  • Model from access patterns: data read together should usually live together.
  • Embed for bounded one-to-few data; reference for unbounded growth or independent lifecycle.
  • Build indexes for real queries, not theoretical flexibility. Use ESR ordering for equality -> sort -> range compound indexes.
  • Use transactions only when single-document guarantees are insufficient.

Verify

  • Embed vs reference choice matches cardinality and lifecycle.
  • Compound index order matches equality -> sort -> range access.
  • Large pagination uses cursor patterns, not deep skip().
  • Explain output supports the chosen indexes; review keysExamined and docsExamined.
  • Unbounded arrays and hot shard keys were reviewed.

Anti-Patterns

  • No unbounded arrays: Use $push with $slice or redesign using Bucket Pattern.
  • No client-side filtering: Project only needed fields; never fetch full docs to filter in memory.
  • No deep nesting: Keep nesting ≤4 levels; flatten paths that frequently queried.
  • No index cargo cult: each index must map to a read path and write tradeoff.

References