Question

我开始学习使用实体图来减少N + 1问题。但是我遇到了一个问题，即findAll方法返回重复数据。

person

@Entity
public class Person {
    @Id
    @GeneratedValue
    public long id;
    public String name;

    @ManyToOne(fetch = FetchType.LAZY,cascade = CascadeType.ALL)
    @JoinColumn(name = "department_id")
    @JsonIgnore
    public Department department;

department

@Entity
@NamedEntityGraph(name = "department.p",attributeNodes = 
@NamedAttributeNode(value = "people"))
public class Department {
    @Id
    @GeneratedValue
    @Column(name = "department_id")
    private long id;

    private String name;

    @OneToMany(fetch = FetchType.LAZY,cascade = 
        CascadeType.ALL,mappedBy = "department")
    private List<Person> people = new ArrayList<>();

我创建了一个departmentrepo

interface DepartmentRepository extends CrudRepository<Department,Long> {

@EntityGraph(value = "department.p", type = 
     EntityGraph.EntityGraphType.LOAD)
    List<Department> findAll();
}

pom.xml

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

我的代码有什么问题？方法findAll不能使用EntityGraph？

Answer 1

方法1：

我们可以使用DISTINCT关键字删除重复数据

方法2：

我们可以使用set集合。我找到了一种以休眠形式访问remove duplicate data的方法，并且这种方法为我们提供了一个原因，使休眠方式创建重复数据。

如何在spring数据jpa中使用实体图

1 个答案: