Fetching All Entity Attributes As Spring Projection (DTO)

Description: This application is a sample of fetching all attributes of an entity (Author) as a Spring projection (DTO). Commonly, a DTO contains a subset of attributes, but, sometimes we need to fetch the whole entity as a DTO. In such cases, we have to pay attention to the chosen approach. Choosing wisely can spare us from performance penalties.

Key points:

• fetching the result set as a List<Object[]> or List<AuthorDto> via a JPQL of type SELECT a FROM Author a WILL fetch the result set as entities in Persistent Context as well - avoid this approach
• fetching the result set as a List<Object[]> or List<AuthorDto> via a JPQL of type SELECT a.id AS id, a.name AS name, ... FROM Author a will NOT fetch the result set in Persistent Context - this is efficient
• fetching the result set as a List<Object[]> or List<AuthorDto> via a native SQL of type SELECT id, name, age, ... FROM author will NOT fetch the result set in Persistent Context - but, this approach is pretty slow
• fetching the result set as a List<Object[]> via Spring Data query builder mechanism WILL fetch the result set in Persistent Context - avoid this approach
• fetching the result set as a List<AuthorDto> via Spring Data query builder mechanism will NOT fetch the result set in Persistent Context
• fetching the result set as read-only entitites (e.g., via the built-in findAll() method) should be considered after JPQL with explicit list of columns to be fetched and query builder mechanism

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