Neo4j 一对多获取数据

Question

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;


}

并且我有以下 SDN 存储库方法：

@Query("MATCH (d:Decision)<-[:VOTED_FOR]-(v:Vote)-[:VOTED_ON]->(c:Criterion) WHERE id(d) = {decisionId} AND id(c) = {criterionId} RETURN v")
List<Vote> getVotes(@Param("decisionId") Long decisionId, @Param("criterionId") Long criterionId);

在结果中我有一个列表 Vote。

在客户端上，我想显示这些投票的列表，不仅有用户（作者）Id，还有作者 username。

如何根据上述 Vote.author.username 和 Vote.author.id 的查询进行提取，而不从与 Vote 实体关联的 User 实体中提取所有其他信息？不管怎样，现在我只有Vote.author.id值。

已编辑：

后续查询

@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, `decision.id` : d.id, `criterion.id` : c.id, `author.id`: u.id, `author.username`: u.username} as v")
List<Vote> getVotesForDecisionOnCriterion(@Param("decisionId") Long decisionId, @Param("criterionId") Long criterionId);

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.underlyingObjectToObject(QueryResultBuilder.java:86)

Answer 1

我帮不上忙 spring 但是这个密码能满足您的需求吗？

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

Answer 2

尝试使用 DTO（也可以是带有 getter 的接口）：

@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);

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