The N + 1 query problem occurs when one query retrieves a collection and an additional query retrieves related data for every item. Query count therefore grows linearly with the records displayed, adding database overhead to each request. section 6.4.1
Recognize the pattern through its common implementation path:
- A request queries a list of parent objects. section 6.4.1
- Lazy loading retrieves each parent’s related child objects separately, producing one query per item. section 6.4.1
- Batch the related data with a JOIN or a second query so each request uses a small constant number of queries. section 6.4.1
Rendering a list
A page first queries a list of objects, then lazily queries each object’s children. For N objects, the request performs one list query plus N child queries; eager loading or batched retrieval reduces this to a constant number. section 6.4.1
