DB Antipatterns

db-antipatterns (M19) — unified anti-pattern catalog

M19 is the catch-all for recognized anti-patterns that span paradigms and don't sit cleanly inside one structural module. It does not own a weight of its own. Findings inherit the category of the most natural module: an EAV smell is a modeling/normalization problem → it scores under M1 (Modelado, design); a Mongo unbounded-array smell scores under document Crecimiento-doc (performance); polymorphic associations without an FK score under M3 (Integridad referencial, both). The finding's module stays M19 for provenance, but expected_impact.axis and the rule id's intent route it to the owning category at scoring time. This avoids double-counting — a single smell contributes to exactly one category per axis. See references/scoring-model.md for the category map per paradigm.

What it checks (catalog)

Relational / SQL:

• EAV (entity-attribute-value) generic (entity, attribute, value) tables replacing real columns → re-homes to M1 (design). Defeats types, constraints, indexing.
• God table — one table with dozens-to-hundreds of columns, many nullable → M1 (design).
• CSV-in-a-column — tags VARCHAR holding "a,b,c" instead of a child table/array/jsonb → M1/M4.
• Polymorphic association without FK (commentable_type + commentable_id, no constraint) → M3 (both).
• Boolean-flag soup — many is_* booleans that should be a state enum/lookup → M4 (design).
• Magic catch-all jsonb/text blob used as schema evasion → re-homes to M4 (design). NoSQL:
• Mongo unbounded array growth — arrays that grow without bound toward the 16 MB doc cap → document Crecimiento-doc (performance).
• Deep nesting / massive embedded docs that should be referenced collections → document Access-pattern & embedding (design).
• App-side join / fan-out — N reads to stitch documents that a different model would co-locate → document Query (performance, directional/structural).
• Redis as durable primary store — relied-on data with no AOF/RDB durability path → key-value Durabilidad (perf). Sev-5 only with live evidence of durability config; else directional.

Tier-0 static checks

Parse the schema/ORM (scripts/parse-schema.mjs, parse-orm-python.py). Flag: a table whose columns are literally (entity_id, attribute, value); column count above a high threshold with mostly-nullable columns; string columns named tags/roles/csv; *_type + *_id pairs with no matching FK; ≥N is_*/has_* booleans on one table; Mongoose schemas with array-of-subdocument fields and no cap.

Tier-1 verification query

• Postgres god table: SELECT relname, count(*) AS cols FROM information_schema.columns JOIN pg_class ON relname=table_name GROUP BY relname ORDER BY cols DESC;
• Mongo array growth (Tier-1/2): db.coll.aggregate([{$project:{n:{$size:"$items"}}},{$group:{_id:null,max:{$max:"$n"},avg:{$avg:"$n"}}}]) and db.coll.stats() for avg doc size trending toward 16 MB.
• Redis durability: CONFIG GET save and CONFIG GET appendonly (needs live; else needs_api).

Findings

Emit per schema/finding.schema.json. Example ids:

• M19.events.eav_table — generic EAV table (warn, severity 3, axis design, confidence directional, re-homes to Modelado/M1).
• M19.comments.polymorphic_no_fk — commentable_type/commentable_id with no FK (fail, severity 4, axis both, re-homes to M3).
• M19.feed.unbounded_array — Mongo array trending toward 16 MB (warn, severity 4, axis performance, re-homes to document Crecimiento-doc; sev-5 only with live size evidence). Each finding: evidence.observed quotes the real DDL/Mongoose schema/query verbatim with secrets redacted; verification.reproduce is one of the runnable commands above (referencing $DATABASE_URL); verification.method is ddl_parse, schema_introspect, or manual_review; expected_impact is {axis, confidence, magnitude (high|medium|low), rationale} — banded, never a naked %.

Honesty

• Never call a pattern an anti-pattern without naming the workload it harms; EAV, denormalized blobs, and embedded arrays are legitimate in the right context. State the assumption.
• A directional structural smell (e.g. app-side fan-out inferred from ORM source) never caps a score. Redis-undurable and unbounded-array sev-5 require live evidence; otherwise directional or needs_api, never a silent pass.