Debug Ecto constraint violations – trace triggers, check migrations, find duplicate data.
Debug Ecto constraint violations - trace triggers, check migrations, find duplicate data. Use when seeing unique_constraint, foreign_key_constraint, or check_constraint errors.This is the skill's description: the text your AI reads to decide when the skill applies.
elixir-ecto-constraint-debug/SKILL.md
---
name: ecto:constraint-debug
description: Debug Ecto constraint violations - trace triggers, check migrations, find duplicate data. Use when seeing unique_constraint, foreign_key_constraint, or check_constraint errors.
effort: medium
---
# Ecto Constraint Debugging
> **Ash projects**: Ash surfaces DB constraints through its own error DSL. Use the `ash-framework` skill — `mix usage_rules.search_docs "constraint" -p ash_postgres`.
Systematic approach to diagnosing constraint violations. Load when you see `Ecto.ConstraintError`, `unique_constraint`, `foreign_key_constraint`, or constraint-related changeset errors.
## Iron Laws
1. **READ THE CONSTRAINT NAME** — The constraint name (e.g., `links_url_index`) tells you exactly which index/constraint failed. Parse it from the error message first
2. **CHECK MIGRATION BEFORE CODE** — Verify the constraint definition in `priv/repo/migrations/` matches what the schema expects
3. **TRACE ALL INSERT PATHS** — Find every code path that inserts into the constrained table. The bug is often in a path you didn't consider
4. **RACE CONDITION UNTIL PROVEN OTHERWISE** — If validation passes but constraint fails, assume concurrent inserts until you prove a single-request cause
## Step-by-Step Debugging
### Step 1: Parse the Error
Extract from the error message:
… load the full skill through Skill Me