ecto-constraint-debug

# 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: - **Constraint name** (e.g., `users_email_index`) - **Table name** (e.g., `users`) - **Operation** (insert, update, or delete) - **Conflicting values** (if available in logs) ### Step 2: Find the Migration Use Grep to search for the constraint name in `priv/repo/migrations/`. Also check for `create unique_index`, `create index`, `add constraint`. Verify: Does the migration constraint match the schema's `unique_con...