SpringBoot基础之Spring Data Jpa

今天讲一下Spring Data Jpa的基础写法，实际上很easy，很多语句都可以用DSL来替换，很有意思。

在Springboot启动类加上@EnableJpaRepositories可以直接允许使用Spring Data Jpa
下面这个是常见的Jpa的Repository的写法

public interface LocationJpaRepository extends JpaRepository<Location, Long> {
}

Entity配置，@Id表示主键，@GeneratedValue(strategy = GenerationType.AUTO)表示自增长，@Column表示字段名称
@OneToMany表示一对多的关系

@Entity
@Table(name = "APPLICATION")
public class Application {
    public Application() { }
    public Application(String name, String description, String owner) {
        this.name = name;
        this.description = description;
        this.owner = owner;
    }
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "application_id")
    private Integer id;
    @Column(name = "app_name", nullable = false)
    private String name;
    @Column(length = 2000)
    private String description;
    private String owner;
    @Override
    public String toString() {
        return "Application{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", description='" + description + '\'' +
                ", owner='" + owner + '\'' +
                '}';
    }
}

@OneToMany需要有@ManyToOne对应，其中会有ManyToOne的表Exercise中增加外键索引，application_application_id，另外FetchType.LAZY表示只有在通过getExercises时才去表中查询，如果是FetchType.EAGER表示获取到application时就要同时去表中查询exercises

public class Application {
    @OneToMany(mappedBy = "goal", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Exercise> exercises = new ArrayList<Exercise>();
}
public class Exercise {
    @ManyToOne
    private Application application;
}

增删改查操作CRUD

location loc;
Long id;
//save
locationJpaRepository.saveAndFlush(loc);//或者save
//update
locationJpaRepository.saveAndFlush(loc);//或者save
//delete
locationJpaRepository.delete(loc);
//find
locationJpaRepository.findOne(id);

DSL，其中State必须与Location中的字段完全一致即可直接使用模糊查询方法

List<Location> findByStateLike(String stateName);
//执行时需要增加like需要的%
locationJpaRepository.findByStateLike("dfdf%");

DSL中有很多关键字

1. findBy表示通过By后面的字段来查询
2. And与SQL中的and意义相同，findByStateAndCity(String value1, String value2)，等同SQL语句为：where a.state = ? and a.city = ?
3. Or与SQL中的or意义相同,findByStateOrCity(String value1, String value2)，等同SQL语句为：where a.state = ? or a.city = ?
4. Equals和不带任何参数的意义相同，findByStateEquals(String value)，等同SQL语句为：where a.state = ?
5. Is和equals意义相同，findByStateIs(String value)，等同SQL语句为：where a.state = ?
6. Not与SQL中的<>意义相同，findByStateIs(String value)，等同SQL语句为：where a.state <> ?
7. Like与SQL中的like意义相同，findByStateLike("New%")，等同SQL语句为：where a.state like ?
8. NotLike与SQL中的not like意义相同，findByStateNotLike("New%")，等同SQL语句为：where a.state not like ?
9. StartingWith与SQL中的like意义相同，findByStateStartingWith("New")，等同SQL语句为：where a.state not like '%?'
10. EndingWith与SQL中的like意义相同，findByStateEndingWith("New")，等同SQL语句为：where a.state not like '?%'
11. Containing与SQL中的like意义相同，findByStateContaining("New")，等同SQL语句为：where a.state not like '%?%'
12. LessThan与SQL中的<意义相同，findByPriceLessThan(BigDemical big)，等同SQL语句为：where a.price < ?
13. LessThanEqual与SQL中的<=意义相同，findByPriceLessThanEqual(BigDemical big)，等同SQL语句为：where a.price <= ?
14. GreaterThan与SQL中的>意义相同，findByPriceGreaterThan(BigDemical big)，等同SQL语句为：where a.price > ?
15. GreaterThanEqual与SQL中的>=意义相同，findByPriceGreaterThanEqual(BigDemical big)，等同SQL语句为：where a.price >= ?
16. Before与SQL中比较日期的<意义相同，findByFoundedDateBefore(Date date)，等同SQL语句为：where a.date < ?
17. After与SQL中比较日期的>意义相同，findByFoundedDateAfter(Date date)，等同SQL语句为：where a.date > ?
18. Between与SQL中比较日期的between and意义相同，findByFoundedDateBetween(Date date1,Date date2),
等同SQL语句为：where a.date between ? and ?
19. True与SQL中比较Boolean的=true意义相同，findByActiveTrue()，等同SQL语句为：where a.active = true
20. False与SQL中比较Boolean的=false意义相同，findByActiveFalse()，等同SQL语句为：where a.active = false
21. IsNull与SQL中比较的is null意义相同，findByActiveIsNull()，等同SQL语句为：where a.active is null
22. IsNotNull与SQL中比较的is not null意义相同，findByActiveIsNotNull()，等同SQL语句为：where a.active is not null
23. NotNull与SQL中比较的is not null意义相同，findByActiveNotNull()，等同SQL语句为：where a.active is not null
24. In与SQL中比较的in意义相同，findByStateIn(Collection<String> states)，等同SQL语句为：where a.state in ?
25. NotIn与SQL中比较的not in意义相同，findByStateNotIn(Collection<String> states)，等同SQL语句为：where a.state not in ?
其中有一个特殊的情况，Model类其中组合了ModelType类，因此可以通过ModelType来获取Model，List<Model> models = findByModelTypeNameIn(List<String> modelTypeName)
26. IgnoreCase，findByStateIgnoreCase(String state)，等同SQL语句为：where UPPER(a.state) = UPPER(?)
27. StartingWithIgnoreCase，findByStateStartingWithIgnoreCase(String state)，等同SQL语句为：where UPPER(a.state) like UPPER('?%')
28. OrderByCountryAsc，findByStateOrderByCountryAsc(String state) ,等同于SQl语句为：whrere a.state = ? order by a.country asc
29. OrderByCountryDesc，findByStateOrderByCountryDesc(String state),等同于SQl语句为：whrere a.state = ? order by a.country desc
30. First，findFirstByState(String state),等同于SQl语句为：whrere a.state = ? limit 1
31. Top5，findTop5ByState(String state),等同于SQl语句为：whrere a.state = ? limit 5
32. Distinct，findDistinctManufacturerByState(String state),等同于SQl语句为：select discint manufacturer *** whrere a.state = ?

不实用DQL可以通过@Query注解自定义JPQL语句，@Param指定参数对应JPQL中的：后边的参数

@Query("select m from Model m where m.price >= :lowest and m.price <= :highest and m.woodType like :wood ")
List<Model> queryByPriceRangeAndWoodType(@Param("lowest")BigDecimal lowest,
                                         @Param("highest")BigDecimal high,
                                         @Param("wood")String wood);

通过Entity的NamedQuery方法定义的JPQL语句可以在ModelJpaRepository中直接实现，需要传入制定的参数

@Entity
@NamedQuery(name="Model.findAllModelsByType", query="select m from Model m where m.modelType.name = :name")
public class Model {
}
@Repository
public interface ModelJpaRepository extends JpaRepository<Model,Long> {
    public List<Model> findAllModelsByType(@Param("name") String name);
}

通过Entity的NamedNativeQuery方法定义的原生SQL语句可以在ModelJpaRepository中直接实现，需要传入制定的参数

@Entity
@NamedNativeQuery(name = "Manufacturer.getAllThatSellAcoustics", 
      query = "SELECT m.id, m.name, m.foundedDate, m.averageYearlySales, m.location_id as headquarters_id "
       + "FROM Manufacturer m "
      + "LEFT JOIN Model mod ON (m.id = mod.manufacturer_id) "
      + "LEFT JOIN ModelType mt ON (mt.id = mod.modeltype_id) "
       + "WHERE (mt.name = ?)", resultClass = Manufacturer.class)
public class Manufacturer {
}
@Repository
public interface ManufacturerJpaRepository extends JpaRepository<Manufacturer,Long> {
    List<Manufacturer> getAllThatSellAcoustics(String name);
}

所有带@Query的都是需要原生SQL处理的，而默认不带@Query的都是DSL标准的方法，如果使用原生SQL，需要增加nativeQuery = true
分页方法，需要在Repository的方法中增加Pageable方法

@Repository
public interface ModelJpaRepository extends JpaRepository<Model, Long> {
    @Query("select m from Model m where m.price >= :lowest and m.price <= :highest and m.woodType like :wood ")
    Page<Model> queryByPriceRangeAndWoodType(@Param("lowest")BigDecimal lowest,
                                             @Param("highest")BigDecimal high,
                                             @Param("wood")String wood,
                                             Pageable page);
}
//service方法，Sort为排序方式，创建PageRequest，第一个为页数，第二个每页展示个数，第三个是排序方式
public Page<Model> queryByPriceRangeAndWoodType(BigDecimal lowest,BigDecimal highest, String wood){
   Sort sort = new Sort(Sort.Direction.ASC, "name");
   Pageable page = new PageRequest(0,2, sort);
   return locationJpaRepository.queryByPriceRangeAndWoodType(lowest, highest, wood,page);
}

锁，有几种情况的锁，乐观悲观等

@Repository
public interface ModelJpaRepository extends JpaRepository<Model,Long> {
    @Lock(LockModeType.PESSIMISTIC_WRITE)
    public List<Model> findAllModelsByType(@Param("name") String name);
}