介紹
Spring Data JPA 是 Spring 基於 ORM 框架、JPA 規範的基礎上封裝的一套JPA應用框架，可使開發者用極簡的程式碼即可實現對資料的訪問和操作。它提供了包括增刪改查等在內的常用功能，且易於擴充套件！學習並使用 Spring Data JPA 可以極大提高開發效率！
spring data jpa讓我們解脫了DAO層的操作，基本上所有CRUD都可以依賴於它來實現
基本查詢
基本查詢也分為兩種，一種是spring data預設已經實現，一種是根據查詢的方法來自動解析成SQL。
自定義簡單查詢
自定義的簡單查詢
就是根據方法名來自動生成SQL，主要的語法是findXXBy,readAXXBy,queryXXBy,countXXBy, getXXBy後面跟屬性名稱：
基本上SQL體系中的關鍵詞都可以使用，例如：LIKE、 IgnoreCase、 OrderBy。
List<User> findByEmailLike(String email);
User findByUserNameIgnoreCase(String userName);
List<User> findByUserNameOrderByEmailDesc(String email修改、刪除、統計也是類似語法
Long deleteById(Long id);
Long countByUserName(String userName)具體的關鍵字，使用方法和生產成SQL如下表所示
具體的關鍵字，使用方法和生產成SQL如下表所示
| Keyword | Sample | JPQL snippet |
|---|---|---|
| And | findByLastnameAndFirstname | … where x.lastname = ?1 and x.firstname = ?2 |
| Or | findByLastnameOrFirstname | … where x.lastname = ?1 or x.firstname = ?2 |
| Is,Equals | findByFirstnameIs,findByFirstnameEquals | … where x.firstname = ?1 |
| Between | findByStartDateBetween | … where x.startDate between ?1 and ?2 |
| LessThan | findByAgeLessThan | … where x.age < ?1 |
| LessThanEqual | findByAgeLessThanEqual | … where x.age ⇐ ?1 |
| GreaterThan | findByAgeGreaterThan | … where x.age > ?1 |
| GreaterThanEqual | findByAgeGreaterThanEqual | … where x.age >= ?1 |
| After | findByStartDateAfter | … where x.startDate > ?1 |
| Before | findByStartDateBefore | … where x.startDate < ?1 |
| IsNull | findByAgeIsNull | … where x.age is null |
| IsNotNull,NotNull | findByAge(Is)NotNull | … where x.age not null |
| Like | findByFirstnameLike | … where x.firstname like ?1 |
| NotLike | findByFirstnameNotLike | … where x.firstname not like ?1 |
| StartingWith | findByFirstnameStartingWith | … where x.firstname like ?1 (parameter bound with appended %) |
| EndingWith | findByFirstnameEndingWith | … where x.firstname like ?1 (parameter bound with prepended %) |
| Containing | findByFirstnameContaining | … where x.firstname like ?1 (parameter bound wrapped in %) |
| OrderBy | findByAgeOrderByLastnameDesc | … where x.age = ?1 order by x.lastname desc |
| Not | findByLastnameNot | … where x.lastname <> ?1 |
| In | findByAgeIn(Collection<Age> ages)</Age> | … where x.age in ?1 |
| NotIn | findByAgeNotIn(Collection<Age> age)</Age> | … where x.age not in ?1 |
| TRUE | findByActiveTrue() | … where x.active = true |
| FALSE | findByActiveFalse() | … where x.active = false |
| IgnoreCase | findByFirstnameIgnoreCase | … where UPPER(x.firstame) = UPPER(?1) |