ecto-essentials

Ecto Essentials

RULES — Follow these with no exceptions

1. Always use changesets for inserts and updates — never pass raw maps to Repo
2. Preload associations before accessing them — avoid N+1 queries
3. Use transactions for multi-step operations that must succeed together
4. Add database constraints (unique_index, foreign_key, check_constraint) AND changeset validations
5. Use contexts for database access — never call Repo directly from web layer
6. Add indexes on foreign keys and frequently queried fields
7. Use timestamps() in every schema — track when records were created/updated

---

Schema Definition

Define schemas with proper types and associations.

defmodule MyApp.Media.Image do
  use Ecto.Schema
  import Ecto.Changeset

  schema "images" do
    field :title, :string
    field :description, :string
    field :filename, :string
    field :file_path, :string
    field :content_type, :string
    field :file_size, :integer

    belongs_to :folder, MyApp.Media.Folder

    timestamps()
  end
end

Changesets

Always use changesets for data validation and casting.

def changeset(image, attrs) do
  image
  |> cast(attrs, [:title, :description, :filename, :file_path, :content_type, :file_size, :folder_id])
  |> validate_required([:title, :filename, :file_path, :content_type, :file_size])
  |> validate_length(:title, min: 1, max: 255)
  |> validate_inclusion(:content_type, ["image/jpeg", "image/png", "image/gif"])
  |> validate_number(:file_size, greater_than: 0, less_than: 10_000_000)
  |> foreign_key_constraint(:folder_id)
end

Query Composition

Build queries composably using Ecto.Query.

import Ecto.Query

def list_images_by_folder(folder_id) do
  Image
  |> where([i], i.folder_id == ^folder_id)
  |> order_by([i], desc: i.inserted_at)
  |> Repo.all()
end

def search_images(query_string) do
  search = "%#{query_string}%"

  Image
  |> where([i], ilike(i.title, ^search) or ilike(i.description, ^search))
  |> Repo.all()
end