使用JDO在GAE中进行双向一对一映射？

Question

如何使用Google Application Engine (GAE) 和Java Data Objects (JDO) 实现双向一对一映射？

我有一个包含contactInfo 对象的User 类和一个包含user 对象的ContactInfo 类

@PersistenceCapable(identityType ="APPLICATION", detachable = "true")
public class User{
  @PrimaryKey
  @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
  private Long id;

  private String name;

  @Persistent(dependent = "true")
  private ContactInfo child;

  public Long getId() {
    return id;
  }

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

  public String getName() {
    return name;
  }

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

  public ContactInfo getChild() {
    return child;
  }

  public void setChild(ContactInfo child) {
    this.child = child;
  }
}


@PersistenceCapable(identityType ="APPLICATION", detachable = "true")
public class ContactInfo {
  @PrimaryKey
  @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
  private Key id;

  @Persistent(mappedBy = "child")
  private User parent;

  private String contactDetail;

  public Key getId() {
    return id;
  }

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

  public String getContactDetail() {
    return contactDetail;
  }

  public void setContactDetail(String contactDetail) {
    this.contactDetail = contactDetail;
  }
}

我在从 API 资源管理器测试 API 时遇到以下错误

com.google.appengine.repackaged.org.codehaus.jackson.map.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: com.demo.jdo.ContactInfo[\"user\"]->com.demo.jdo.User[\"contactInfo\"]->com.demo.jdo.ContactInfo[\"user\"]-

Answer 1

标准 JDO 1-1 bidir 简单地从http://www.datanucleus.org/products/accessplatform_3_1/jdo/orm/one_to_one.html#bi 找到 GAE 在这方面应该没有什么不同。我上次使用它时（可能是 3 年前），他们进行了一些测试，想想下面的那些 http://code.google.com/p/datanucleus-appengine/source/browse/#svn%2Ftrunk%2Ftests%2Fcom%2Fgoogle%2Fappengine%2Fdatanucleus

您的问题没有提供您在注释方面尝试过的定义

Answer 2

找到了解决方案，问题在于错误使用 mappedBy 以及子对象中存在 getter 和 setter。

• @Persistent(mappedBy = "") 注释只能在非所有者方
• 在所有者/子方面，所有者/父对象不应存在任何 getter/setter。

工作代码：

User.java

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class User {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
private String name;

@Persistent(dependent = "true")
private ContactInfo contactInfo;

public Long getId() {
    return id;
}

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

public String getName() {
    return name;
}

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

public ContactInfo getContactInfo() {
    return contactInfo;
}

public void setContactInfo(ContactInfo contactInfo) {
    this.contactInfo = contactInfo;
}
}

ContactInfo.java

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

import com.google.appengine.api.datastore.Key;

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class ContactInfo {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key id;

    @Persistent(mappedBy = "contactInfo")
    /*
     * Important: Do not create getter and setters for this object else
     * bidirectional mapping gives error
     */
    private User user;

    private String contactDetail;

    public Key getId() {
        return id;
    }

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

    public String getContactDetail() {
        return contactDetail;
    }

    public void setContactDetail(String contactDetail) {
        this.contactDetail = contactDetail;
    }
}