MongoDB不能将复杂对象用作Java的键值

我正在实现一个表示要存储在MongoDb中的图形的对象。下面是类定义：

@Document(collection = "mygraph")
public class MyGraph {

    @Id
    @JsonSerialize(using = ToStringSerializer.class)
    public String id;
    public Map<Instance, Set<Instance>> graph;
    public String timestamp;

    /**
     * Add the default constructor
     */
    public MyGraph() {
        this.id = new ObjectId().toHexString();
        this.graph = new LinkedHashMap<>();
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        this.timestamp = dateFormat.format(new Date());
    }

        /**
     * 
     * @param instances
     */
    public MyGraph(Set<Instance> instances) {
        this.id = new ObjectId().toHexString();
        this.graph = new LinkedHashMap<>();
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        this.timestamp = dateFormat.format(new Date());

        /* Initialize the graph */
        for (Instance instance : instances) {
            this.graph.put(instance, new HashSet<>());
        }
    }
    // get and set method are below
} 

@文档（collection=“mygraph”）
公共类MyGraph{
@身份证
@JsonSerialize（使用=ToStringSerializer.class）
公共字符串id；
公共地图；
公共字符串时间戳；
/**
*添加默认构造函数
*/
公共MyGraph（）{
this.id=new ObjectId（）.toHexString（）；
this.graph=新建LinkedHashMap（）；
DateFormat DateFormat=新的简化格式（“yyyy/MM/dd HH:MM:ss”）；
this.timestamp=dateFormat.format（new Date（））；
}
/**
* 
*@param实例
*/
公共MyGraph（集合实例）{
this.id=new ObjectId（）.toHexString（）；
this.graph=新建LinkedHashMap（）；
DateFormat DateFormat=新的简化格式（“yyyy/MM/dd HH:MM:ss”）；
this.timestamp=dateFormat.format（new Date（））；
/*初始化图形*/
例如（实例：实例）{
this.graph.put（实例，new HashSet（））；
}
}
//获取和设置方法如下所示
} 

但是，我得到了以下错误：

Time elapsed: 0.03 sec  <<< FAILURE!
org.springframework.data.mapping.model.MappingException: Cannot use a complex object as a key value.
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeMapInternal(MappingMongoConverter.java:669)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.createMap(MappingMongoConverter.java:585)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writePropertyInternal(MappingMongoConverter.java:471)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:430)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:418)
    at org.springframework.data.mapping.model.BasicPersistentEntity.doWithProperties(BasicPersistentEntity.java:312)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:418)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:392)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.write(MappingMongoConverter.java:356)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.write(MappingMongoConverter.java:79)
    at org.springframework.data.mongodb.core.MongoTemplate.toDbObject(MongoTemplate.java:853)
    at org.springframework.data.mongodb.core.MongoTemplate.doSave(MongoTemplate.java:1014)
    at org.springframework.data.mongodb.core.MongoTemplate.save(MongoTemplate.java:963)
    at org.springframework.data.mongodb.repository.support.SimpleMongoRepository.save(SimpleMongoRepository.java:80)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:503)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:488)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:460)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
    at com.sun.proxy.$Proxy197.save(Unknown Source)
    at models.CloudGraphTest.testSaveCloudGraph(CloudGraphTest.java:79)

---

经过的时间：0.03秒Spring中有一个公开的改进：

不幸的是，目前Spring团队决定不支持它

决定根本不支持它

编辑

有一个与开放相关的问题，可能包括稍后的修复
您的MappingMongoConverter在哪里？你是否已经写了一个，但没有工作？你的CloudGraphTest课程在哪里？