ecto-patterns
Ecto patterns — schemas, changesets, queries, migrations, Multi, associations, preloads, upserts. Use when editing Repo calls, Ecto.Query, or schema fields. Skip for Ash.
npx skills add oliver-kriska/claude-elixir-phoenix --skill ecto-patterns --agent claude-code
Same command for any agent — swap --agent for codex, cursor, copilot.
Weekly change comes from our own snapshots, not the repository page — it measures attention, not adoption.
# Ecto Patterns Reference Reference for working with Ecto schemas, queries, and migrations. ## Iron Laws — Never Violate These 1. **CHANGESETS ARE FOR EXTERNAL DATA** — Use `cast/4` for user/API input, `change/2` or `put_change/3` for internal trusted data 2. **NEVER USE `:float` FOR MONEY** — Always use `:decimal` or `:integer` (cents) 3. **NO RAILS-STYLE POLYMORPHIC ASSOCIATIONS** — They break foreign key constraints; use multiple nullable FKs or separate join tables 4. **ALWAYS PIN VALUES IN QUERIES** — `u.name == ^user_input` is safe, string interpolation causes SQL injection 5. **PRELOAD COLLECTIONS, NOT INDIVIDUALS** — Preloading in loops = N+1 queries 6. **CONSTRAINTS BEAT VALIDATIONS FOR RACE CONDITIONS** — Validations provide quick feedback, constraints provide DB-level safety 7. **SEPARATE QUERIES FOR `has_many`, JOIN FOR `belongs_to`** — Avoids row multiplication 8. **NO IMPLICIT CROSS JOINS** — `from(a in A, b in B)` without `on:` creates Cartesian product 9. **DEDUP BEFORE `cast_assoc` WITH SHARED DATA** — When multiple parents share child data, deduplicate child records BEFORE building changesets. Dedup only works within a single changeset ## Quick Schema Template ```
- Iron Laws — Never Violate These
- Quick Schema Template
- Quick Decisions
- cast vs putchange vs change
- Preload Strategy
- Common Anti-patterns
- References
What does the ecto-patterns skill do?
Ecto patterns — schemas, changesets, queries, migrations, Multi, associations, preloads, upserts. Use when editing Repo calls, Ecto.Query, or schema fields. Skip for Ash.
How do I install it?
Run `npx skills add oliver-kriska/claude-elixir-phoenix --skill ecto-patterns --agent claude-code` — it drops the skill into your project so the agent can pick it up. Swap the --agent value for codex, cursor or copilot if you use one of those.
Where does this skill come from?
From oliver-kriska/claude-elixir-phoenix, a repository with 515 stars. We read it straight from the repository tree rather than a submitted listing, so what you see here is what is actually published.
Is a popular skill a good skill?
Not necessarily. Stars measure attention, not adoption — a repository can trend for a week and be abandoned. That is why we show the weekly change from our own snapshots next to the total, instead of a single flattering number.