JPA JoinColumn与mappedBy

Question

两者之间有什么区别：

@Entity
public class Company {

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

而且

@Entity
public class Company {

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

Answer 1

注释@joincolumn表示此实体是关系的所有者（即：对应的表有一个列，该列带有引用表的外键），而属性mappedby表示此边的实体是关系的反面，并且所有者驻留在“Other”实体中。这也意味着您可以从用“mappedby”（完全双向关系）注释的类中访问另一个表。

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;
}