Rails| Method | Trả về | Nếu không tìm thấy |
|---|---|---|
find(id) | single record | raise ActiveRecord::RecordNotFound |
find_by(attrs) | single record hoặc nil | nil |
where(attrs) | ActiveRecord::Relation (collection) | empty relation |
ruby
User.find(1) # raise nếu id=1 không tồn tại
User.find_by(email: "x") # nil nếu không có
User.where(role: "admin") # Relation — chưa query đến khi cầnLazy evaluation: where không chạy SQL ngay — chỉ build query. SQL thực sự chạy khi gọi to_a, .each, .first, hoặc render.
Dùng find khi ID chắc chắn tồn tại (controller show). Dùng find_by khi có thể nil. Dùng where để chain thêm điều kiện.
| Method | Returns | If not found |
|---|---|---|
find(id) | single record | raises ActiveRecord::RecordNotFound |
find_by(attrs) | single record or nil | nil |
where(attrs) | ActiveRecord::Relation (collection) | empty relation |
ruby
User.find(1) # raises if id=1 doesn't exist
User.find_by(email: "x") # nil if not found
User.where(role: "admin") # Relation — not queried until neededLazy evaluation: where doesn't run SQL immediately — it builds a query object. SQL fires when .to_a, .each, .first, or rendering occurs.
Use find when the ID is guaranteed to exist (controller show). Use find_by when nil is possible. Use where to chain further conditions.