Java 在投影前后对不同模型使用过滤

Question

考虑 hibernate 的以下 JAVA 模型：

@Entity
@Table
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id;

    @Column
    public String firstName;

    @Column
    public String lastName;

    @Column
    public Boolean active;
}

和以下用于API序列化的模型（使用spring boot rest controller）：

public class PersonVO {
    public Long id;
    public String fullName;
}

我想要的是：

对人物应用一些过滤（静态定义）
在 PersonVO 应用一些过滤（从@RequestParam 获取）

在 C# .NET 中，我可以像这样：

IQueryable<Person> personsQuery = entityFrameworkDbContext.Persons;
// FIRST POINT - Here i could make some predefined filtering like 'only active', 'from the same city'... at the database model
personsQueryWithPreDefinedFilters = personsQuery.Where(person => person.active == true);


IQueryable<PersonVO> personsProjectedToVO = personsQueryWithPreDefinedFilters.Select(person => new PersonVO()
{
    id = person.id,
    fullName = person.firstName + " " + person.lastName
});
// SECOND POINT - At this point i could add more filtering based at PersonVO model
if (!String.IsNullOrWhiteSpace(fullNameRequestParameter)) {
    personsProjectedToVO = personsProjectedToVO.Where(personVO => personVO.FullName == fullNameRequestParameter);
}

// The generated SQL at database is with both where (before and after projection)
List<PersonVO> personsToReturn = personsProjectedToVO.ToList();

我在Java中得到的是：

CriteriaBuilder cb = this.entityManager.getCriteriaBuilder();
CriteriaQuery<PersonVO> cq = cb.createQuery(PersonVO.class);
Root<Person> root = cq.from(Person.class);
// FIRST POINT - Here i could make some predefined filtering like 'only active', 'from the same city'... at the database model
cq.where(cb.equal(root.get(Person_.active), true));         

Expression<String> fullName = cb.concat(root.get(Person_.firstName), root.get(Person_.lastName));
cq.select(cb.construct(
        PersonVO.class,
        root.get(Person_.id),
        fullName
        ));
// SECOND POINT - At this point i could add more filtering based at PersonVO model??? HOW???
if (fullNameRequestParameter != null) {
    cq.where(cb.equal(fullName, fullNameRequestParameter));
// i only could use based at the fullName expression used, but could i make a Predicate based only on PersonVO model without knowing or having the expression?
}

我想将 "projection to the VO model" 与应用于它的 "where expression" 分开，但如果使用投影列（如 fullName），则间接应用它。

这在 Java 中可行吗？用什么？标准？查询dsl？溪流？（不一定要坚持 java 样本）

Answer 1

JPA Criteria API 没有这样的功能。还有，读起来不容易

JPA 标准API

在标准 API 中，您需要重复使用 Expression。

工作代码如下所示：

public List<PersonVO> findActivePersonByFullName(String fullName) {
  CriteriaBuilder cb = entityManager.getCriteriaBuilder();
  CriteriaQuery<PersonVO> cq = cb.createQuery(PersonVO.class);
  Root<Person> root = cq.from(Person.class);

  List<Predicate> predicates = new ArrayList<>();
  predicates.add(cb.equal(root.get("active"), true));

  Expression<String> fullNameExp = 
      cb.concat(cb.concat(root.get("firstName"), " "), root.get("lastName"));

  cq.select(cb.construct(
      PersonVO.class,
      root.get("id"),
      fullNameExp
  ));

  if (fullName != null) {
    predicates.add(cb.equal(fullNameExp, fullName));
  }

  cq.where(predicates.toArray(new Predicate[0]));

  return entityManager.createQuery(cq).getResultList();
}

生成的SQL代码：

select
    person0_.id as col_0_0_,
    ((person0_.first_name||' ')||person0_.last_name) as col_1_0_ 
from
    person person0_ 
where
    person0_.active=? 
    and (
        (
            person0_.first_name||?
        )||person0_.last_name
    )=?

JPA 标准 API 和 `@org.hibernate.annotations.Formula`

Hibernate 有一个注释 org.hibernate.annotations.Formula 可以稍微简化代码。

向实体添加一个注释为 @Formula("first_name || ' ' || last_name"):

的计算字段

@Entity
public class Person {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  public Long id;

  @Column
  public String firstName;

  @Column
  public String lastName;

  @Column
  public boolean active;

  @Formula("first_name || ' ' || last_name")
  private String fullName;

  //...getters and setters
}

并且在 JPA Criteria API 查询中引用字段 fullName:

public List<PersonVO> findActivePersonByFullName(String fullName) {
  CriteriaBuilder cb = entityManager.getCriteriaBuilder();
  CriteriaQuery<PersonVO> cq = cb.createQuery(PersonVO.class);
  Root<Person> root = cq.from(Person.class);

  List<Predicate> predicates = new ArrayList<>();
  predicates.add(cb.equal(root.get("active"), true));

  cq.select(cb.construct(
      PersonVO.class,
      root.get("id"),
      root.get("fullName")
  ));

  if (fullName != null) {
    predicates.add(cb.equal(root.get("fullName"), fullName));
  }

  cq.where(predicates.toArray(new Predicate[0]));

  return entityManager.createQuery(cq).getResultList();
}

和生成的SQL:

select
    person0_.id as col_0_0_,
    person0_.first_name || ' ' || person0_.last_name as col_1_0_ 
from
    person person0_ 
where
    person0_.active=? 
    and person0_.first_name || ' ' || person0_.last_name=?

Hibernate 标准API

Hibernate Criteria API（自 Hibernate 5.2 起已弃用，取而代之的是 JPA Criteria API）允许使用别名。但并非所有数据库都允许在 where 子句中使用别名（例如 (full_name || ' ' || last_name) as full_name）。

根据 PostgreSQL docs:

An output column's name can be used to refer to the column's value in ORDER BY and GROUP BY clauses, but not in the WHERE or HAVING clauses; there you must write out the expression instead.

表示SQL查询

select p.id, 
      (p.first_name || ' ' || p.last_name) as full_name 
  from person p
 where p.active = true
   and full_name = 'John Doe'

在 Postgre 中不起作用SQL。

因此，在 where 子句中使用别名不是一种选择。

Answer 2

public interface PersonVO{
  String getFirstName();
  String getLastName();
}

public interface PersonFullNameView{
  PersonVO getFullName();
}

public interface PersonRepository<Person, Long>{

  @Query("SELECT first_name lastName || ' ' || last_name lastName as fullName" + 
         "FROM Person p" +  
         "WHERE p.active = :active AND p.first_name=:firstName AND" + 
         "p.last_name=:lastname"), nativeQuery = true)
  PersonFullNameView methodName(
                     @Param("active" boolean active, 
                     @Param("firstName") String firstName, 
                     @Param("lastName") String lastNam
                     );

}

请注意，您的列名必须等于 "getters" 在接口中（getFirstName = firstName）

它调用基于接口的投影。然后你可以创建 PersonVO:

的实例

PersonFullNameView pfnv = repository.methodName(args...);
PersonVo personVO = pfnv.getFullName();

这是你需要的吗？

Answer 3

使用这个 http://www.jinq.org/ 库我可以做到并应用于休眠（以及数据库）。

JinqJPAStreamProvider jinqJPAStreamProvider = new JinqJPAStreamProvider(this.entityManager.getMetamodel());

JPAJinqStream<Person> personStream = jinqJPAStreamProvider.streamAll(this.entityManager, Person.class);
personStream = personStream.where(person -> person.getFirstName().equals("Joao"));

// The only trouble is that we have to register the Model we want to project to (i believe it could be solved with reflection)
jinqJPAStreamProvider.registerCustomTupleConstructor(PersonVO.class.getConstructor(Long.class, String.class), PersonVO.class.getMethod("getId"), PersonVO.class.getMethod("getFullName"));

JPAJinqStream<PersonVO> personVOStream = personStream.select(person -> new PersonVO(person.getId(), person.getFirstName() + person.getLastName()));
personVOStream = personVOStream.where(person -> person.getFullName().equals("JoaoCarmo"));

List<PersonVO> resultList = personVOStream.toList();

感谢大家的帮助！

Java 在投影前后对不同模型使用过滤

Java using filtering at different models before and after the projection

java

hibernate

projection

querydsl

java-stream

JPA 标准API

JPA 标准 API 和 `@org.hibernate.annotations.Formula`

Hibernate 标准API

Java 在投影前后对不同模型使用过滤

Java using filtering at different models before and after the projection

java

hibernate

projection

querydsl

java-stream

JPA 标准API

JPA 标准 API 和 @org.hibernate.annotations.Formula

Hibernate 标准API

JPA 标准 API 和 `@org.hibernate.annotations.Formula`