spring 数据以复合主键休息

Question

我使用 spring 数据剩余作为 crud。但是当实体有复合主键时，我不知道如何通过给主键来获取实体。

河流class:

@Entity
public class River {
    private RiverPK id;
    private Double length;
    private Timestamp date;
    private String comment;


    @Basic
    @Column(name = "length")
    public Double getLength() {
        return length;
    }

    public void setLength(Double length) {
        this.length = length;
    }

    @Basic
    @Column(name = "date")
    public Timestamp getDate() {
        return date;
    }

    public void setDate(Timestamp date) {
        this.date = date;
    }

    @Basic
    @Column(name = "comment")
    public String getComment() {
        return comment;
    }

    public void setComment(String comment) {
        this.comment = comment;
    }

    @Id
    public RiverPK getId() {
        return id;
    }

    public void setId(RiverPK id) {
        this.id = id;
    }
}

RiverPKclass:

@Embeddable
public class RiverPK implements Serializable {
    private String name;
    private int upcode;
    private int downcode;

    @Column(name = "name")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Column(name = "upcode")
    public int getUpcode() {
        return upcode;
    }

    public void setUpcode(int upcode) {
        this.upcode = upcode;
    }

    @Column(name = "downcode")
    public int getDowncode() {
        return downcode;
    }

    public void setDowncode(int downcode) {
        this.downcode = downcode;
    } 

}

RiverDAO class:

@RepositoryRestResource(path = "river")
public interface RiverDAO extends JpaRepository<River, RiverPK> {
}

然后我可以调用 get http://localhost:8080/river/, and also create new entity to db by call post http://localhost:8080/river/ {river json}

获取河流数据

河流json是：

id": {

    "name": "1",
    "upcode": 2,
    "downcode": 3

},
"length": 4.4,
"date": 1493740800000,
"comment": "6"
}

在spring data rest doc中，应该可以调用get localhost:8080/river/1（主键）获取主键为1的实体。这个可以当实体只有一个主键时工作。但是我的实体河流有复合主键作为 RiverPK。如果我调用 get localhost:8080/river/{name='1',upcode=2,downcode=3}，它 returns 一个错误 "No converter found capable of converting from type [java.lang.String] to type [com.example.db.entity.RiverPK]"，我的意思是 spring 使用{name='1',upcode=2,downcode=3} 作为字符串，但不是 RiverPK 类型。

问题是如何调用 get\put\delete 与其他普通实体一样使用复合主键？

Answer 1

有一个jira问题你可以看看： https://jira.spring.io/browse/DATAREST-598

您可能对这条评论特别感兴趣

https://jira.spring.io/browse/DATAREST-598?focusedCommentId=117740&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-117740

您还可以找到 github link to a sample project. It uses a BackendIdConverter 将复合键转换为字符串并返回。所以诀窍是将您的复合id转换为可用作路径段的字符串。

您可能也对这个答案感兴趣

Answer 2

在学习 Customizing HATEOAS link generation for entities with composite ids 之后，我找到了一个更通用的解决方案。

首先，创建一个 SpringUtil 以从 spring.

获取 bean

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringUtil implements ApplicationContextAware {
    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringUtil.applicationContext == null) {
            SpringUtil.applicationContext = applicationContext;
        }
    }

    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }
}

然后，实现BackendIdConverter。

import com.alibaba.fastjson.JSON;
import com.example.SpringUtil;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.rest.webmvc.spi.BackendIdConverter;
import org.springframework.stereotype.Component;

import javax.persistence.EmbeddedId;
import javax.persistence.Id;
import java.io.Serializable;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.net.URLDecoder;
import java.net.URLEncoder;

@Component
public class CustomBackendIdConverter implements BackendIdConverter {

    @Override
    public boolean supports(Class<?> delimiter) {
        return true;
    }

    @Override
    public Serializable fromRequestId(String id, Class<?> entityType) {
        if (id == null) {
            return null;
        }

        //first decode url string
        if (!id.contains(" ") && id.toUpperCase().contains("%7B")) {
            try {
                id = URLDecoder.decode(id, "UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }

        //deserialize json string to ID object
        Object idObject = null;
        for (Method method : entityType.getDeclaredMethods()) {
            if (method.isAnnotationPresent(Id.class) || method.isAnnotationPresent(EmbeddedId.class)) {
                idObject = JSON.parseObject(id, method.getGenericReturnType());
                break;
            }
        }

        //get dao class from spring
        Object daoClass = null;
        try {
            daoClass = SpringUtil.getBean(Class.forName("com.example.db.dao." + entityType.getSimpleName() + "DAO"));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        //get the entity with given primary key
        JpaRepository simpleJpaRepository = (JpaRepository) daoClass;
        Object entity = simpleJpaRepository.findOne((Serializable) idObject);
        return (Serializable) entity;

    }

    @Override
    public String toRequestId(Serializable id, Class<?> entityType) {
        if (id == null) {
            return null;
        }

        String jsonString = JSON.toJSONString(id);

        String encodedString = "";
        try {
            encodedString = URLEncoder.encode(jsonString, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return encodedString;
    }
}

之后。你可以做你想做的事。

下面有一个示例。

如果实体只有一个属性 pk，你可以使用 localhost:8080/demo/1 正常。根据我的代码，假设 pk 有注解“@Id”。
如果实体有组成pk，假设pk是demoId类型，并且有注解“@EmbeddedId”，可以使用localhost:8080/demo/{demoId json} 到 get/put/delete。而你自己link也会一样。

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