Question

我希望在两个实体，消费者和政策之间建立一对多的关系。一个消费者应该有几个政策。

这是我想要的Consumer JSON对象的一个例子：

<Icon.ToolbarAndroid
              titleColor={'#000000'}
              style={{
                 height: 56,
                 alignSelf: 'stretch',
                 width: 20
               }}
              iconColor={"#fff"}
              iconSize={26}
              rtl={true}
              navIconName={"more-vert"}
              contentInsetStart={50}
              actions={[{title: 'Settings', show: 'always'}, {title: 'Settings 2', show: 'always'}]} />

这是我到目前为止所做的：

政策实体

{
     id : 1,
     name : "Peter",
     endpoint: "123.456.778",
     policies: [
                    {
                       id : 1,
                       name: "policy 01"
                    },
                    {
                       id : 2,
                       name: "policy 02"
                    }
             ]
}

消费者实体

@Entity
public class Policy {
        @Id
        @GeneratedValue
        @Column(name = "id")
        private Integer id;

        @Column(name = "name")
        private String name;

        //getters and setters
    }

我认为这并不难，但我现在尝试几个小时并且无法完成它。我是Spring的新手，所以如果有人能够帮助我，我会非常感激！

Answer 1

@Entity
public class Consumer {

    @OneToMany(mappedBy = "consumer")
    private List<Policy> policies;

}

@Entity
public class Policy {

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn("consumer_id")
    private Consumer consumer;

}

fetch = FetchType.LAZY不是必需的，但是可取的。

我在这里提供了一些基础知识

what is @JoinColumn and how it is used in Hibernate

如果您想要Policy没有Consumer：

您可以使用联接表

@Entity
public class Consumer {

    @OneToMany
    private List<Policy> policies;

}

@Entity
public class Policy {

}

单向关系（Policy表格会有consumer_id列，但Policy类没有Consumer）

@Entity
public class Consumer {

    @OneToMany
    @JoinColumn("consumer_id")
    private List<Policy> policies;

}

@Entity
public class Policy {

}

另外，请注意，如果您想使用Policy作为参考（来自字典），则需要@ManyToMany。

Answer 2

试试这段代码：）

您的消费者类

<div class="info-description">

请注意，在映射的旁边，您应该使用数据库中引用Policy的列的名称，因此，如果它没有policyId，请使用您为其指定的名称

您的政策类

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Spring Data JPA中的一对多关系

2 个答案: