java - JPA JoinColumn 与mappedBy

Question

有什么区别:

@Entity
public class Company {

    @OneToMany(cascade = CascadeType.ALL , fetch = FetchType.LAZY)
    @JoinColumn(name = "companyIdRef", referencedColumnName = "companyId")
    private List<Branch> branches;
    ...
}

和

@Entity
public class Company {

    @OneToMany(cascade = CascadeType.ALL , fetch = FetchType.LAZY, 
    mappedBy = "companyIdRef")
    private List<Branch> branches;
    ...
}

Answer 1

注解@JoinColumn表示该实体是关系的所有者(即:对应的表有一列带有被引用表的外键) ，而属性 mappedBy 表示这一方的实体是关系的反面，所有者位于“另一方”实体中。这也意味着您可以从用“mappedBy”(完全双向关系)注释的类访问另一个表。

特别是，对于问题中的代码，正确的注释如下所示:

@Entity
public class Company {
    @OneToMany(mappedBy = "company",
               orphanRemoval = true,
               fetch = FetchType.LAZY,
               cascade = CascadeType.ALL)
    private List<Branch> branches;
}

@Entity
public class Branch {
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "companyId")
    private Company company;
}