Neo4j一对多获取数据 [英] Neo4j one-to-many fetch data

问题描述

在我的Spring Boot/Neo4j应用程序中，我具有以下实体:

In my Spring Boot/Neo4j application I have a following entities:

@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:

and I have a following SDN repository method:

@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);

结果是我有一个Vote列表.

在客户端上，我不仅要与用户(作者)Id一起显示这些投票的清单，还要与作者username一起显示这些投票的清单.

On the client I'd like to display list of these votes with not only user(author) Id but and with author username also.

如何基于Vote.author.username和Vote.author.id上的查询来获取，并且不从与Vote实体相关联的User实体中获取所有其他信息?无论如何，现在我只有Vote.author.id值.

How to fetch based on the query above Vote.author.username and Vote.author.id and do not fetch all other information from User entity associated with Vote entity? Anyway, right now I only have Vote.author.id value.

已编辑

以下查询

@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);

不适用于以下例外情况:

doesn't work with a following exception:

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)

推荐答案

尝试使用DTO(也可以是与getter的接口):

Try this with a DTO (can also be an interface with getters):

@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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