Neo4j一对多获取数据

在我的Spring Boot/Neo4j应用程序中，我有以下实体：

@NodeEntity
public class User extends BaseEntity {

    private static final String HAS = "HAS";

    @GraphId
    private Long id;

    private String username;

    private String password;

    private String email;

    private String firstName;

    private String lastName;

    @RelatedTo(type = HAS, direction = Direction.OUTGOING)
    private Set<Role> roles = new HashSet<Role>();

....

}


@NodeEntity
public class Vote extends BaseEntity {

    private static final String VOTED_ON = "VOTED_ON";
    private final static String VOTED_FOR = "VOTED_FOR";
    private static final String CREATED_BY = "CREATED_BY";

    @GraphId
    private Long id;

    @RelatedTo(type = VOTED_FOR, direction = Direction.OUTGOING)
    private Decision decision;

    @RelatedTo(type = VOTED_ON, direction = Direction.OUTGOING)
    private Criterion criteria;

    @RelatedTo(type = CREATED_BY, direction = Direction.OUTGOING)
    private User author;

    private double weight;

    private String description;


}

不适用于以下异常：

org.springframework.dao.InvalidDataAccessApiUsageException: [Assertion failed] - entity is required; it must not be null
    at org.springframework.data.neo4j.support.ParameterCheck.notNull(ParameterCheck.java:29)
    at org.springframework.data.neo4j.support.Neo4jTemplate.projectTo(Neo4jTemplate.java:240)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.doConvert(EntityResultConverter.java:73)
    at org.springframework.data.neo4j.conversion.DefaultConverter.convert(DefaultConverter.java:44)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.convert(EntityResultConverter.java:165)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.underlyingObjectToObject(QueryResultBuilder.java:86)

---

我帮不上忙，但这个密码能帮你得到你想要的吗

MATCH (d:Decision)<-[:VOTED_FOR]-(v:Vote)-[:VOTED_ON]->(c:Criterion)
WHERE id(d) = {decisionId} 
  AND id(c) = {criterionId} 
WITH v
MATCH v-[:CREATED_BY]->(u:User)
RETURN {id: v.id
       , weight: v.weight
       , `author.id`: u.id
       , `author.username`: u.username
       ... } as v

匹配（d:决策）（c:标准）
其中id（d）={decisionId}
和id（c）={criterionId}
与v
匹配v-[：创建人]->（u:用户）
返回{id:v.id
重量
，`author.id`:u.id
，`author.username`:u.username
…}as v

尝试使用DTO（也可以是getter接口）：

@QueryResult
类VoteView{
字符串id；
双倍重量；
字符串描述；
字符串decisionId；
字符串标准；
字符串编写器；
字符串authorName；
}
@查询（“MATCH（d:Decision）（c:criteria），其中id（d）={decisionId}和id（c）={criterionId}与v，d，c匹配v-[：CREATED_BY]->（u:User）返回{id:v.id，weight:v.weight，description:v.description，decisionId:d.id，criterionId:c.id，authord:u.id，authorName:u.username}作为v”）
列出GetVotesfordecisionCriterion（@Param（“decisionId”）Long decisionId、@Param（“criterionId”）Long criterionId）；

谢谢，但它将返回两个独立的实体-投票和字符串。但是我正在寻找一个解决方案，如何从您的查询中用u.username填充v.author.username并只返回“v”，我更新了答案并将属性组合到一个映射中…-不，好主意！但我无法让它在以下异常情况下工作：org.springframework.dao.InvalidDataAccessApiUsageException:[断言失败]-需要实体；org.springframework.data.neo4j.support.ParameterCheck.notNull（ParameterCheck.java:29）org.springframework.data.neo4j.support.Neo4jTemplate.projectTo（Neo4jTemplate.java:240）org.springframework.data.neo4j.support.conversion.EntityResultConvert.doConvert（EntityResultConverter.java:73）上的值不能为null。。。如此接近…其中一个项是否为空（即，返回一个空值，且映射中有一个键）？如果这是个问题，你可以合并结果或添加一个案例陈述来消除这个关键问题。我已经更新了我的问题主体。。添加了完整的投票类声明、新的查询和错误stacktraceIn SDN3您不能仅仅创建一个映射并让它假装是一个节点，这就是@QueryResult注释DTO的用途。请参阅文档。我希望避免将用户作为Vote的成员，同时在@QueryResult（Vote，User）中作为单独的实体。。我认为这是多余的。谢谢，可以很好地工作，但是使用以下查询（返回分隔列，而不是映射）@query（“MATCH（d:Decision）（c:criteria），其中id（d）={decisionId}和id（c）={criterionId}与v，d，c匹配v-[：CREATED\BY]>（u:User）返回v.id作为voteId，d.id作为decisionId，c.id作为criterionId，v.weight作为weight，v.description作为description，u.id作为authorName，u.username作为authorName，v.createDate作为createDate，v.updateDate作为updateDate”）列表getVotesfordecisionCriterion（@Param（“decisionId”）Long decisionId，@Param（“criterionId”）Long criterionId）；

org.springframework.dao.InvalidDataAccessApiUsageException: [Assertion failed] - entity is required; it must not be null
    at org.springframework.data.neo4j.support.ParameterCheck.notNull(ParameterCheck.java:29)
    at org.springframework.data.neo4j.support.Neo4jTemplate.projectTo(Neo4jTemplate.java:240)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.doConvert(EntityResultConverter.java:73)
    at org.springframework.data.neo4j.conversion.DefaultConverter.convert(DefaultConverter.java:44)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.convert(EntityResultConverter.java:165)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.underlyingObjectToObject(QueryResultBuilder.java:86)

MATCH (d:Decision)<-[:VOTED_FOR]-(v:Vote)-[:VOTED_ON]->(c:Criterion)
WHERE id(d) = {decisionId} 
  AND id(c) = {criterionId} 
WITH v
MATCH v-[:CREATED_BY]->(u:User)
RETURN {id: v.id
       , weight: v.weight
       , `author.id`: u.id
       , `author.username`: u.username
       ... } as v

@QueryResult
class VoteView {
   String id;
   Double weight;
   String description;
   String decisionId;  
   String criterionId;  
   String authorId;
   String authorName;
}

@Query("MATCH (d:Decision)<-[:VOTED_FOR]-(v:Vote)-[:VOTED_ON]->(c:Criterion) WHERE id(d) = {decisionId} AND id(c) = {criterionId} WITH v, d, c MATCH v-[:CREATED_BY]->(u:User) RETURN {id: v.id, weight: v.weight, description: v.description, decisionId : d.id, criterionId : c.id, authorId: u.id, authorName: u.username} as v")
List<VoteView> getVotesForDecisionOnCriterion(@Param("decisionId") Long decisionId, @Param("criterionId") Long criterionId);