使用自定义查询结果对象"Cannot extract single value from Iterable"

Question

我正在使用SpringDataNeo4J 3.0.0-M1和Neo4J2.00-M0.6。

我有BetDAO节点，链接到具有BET_ANSWER关系的BetAnswerDAO节点集合。

我正在尝试检索同一请求上的赌注及其所有答案。我有一个带有以下请求的投注存储库：

@Query("start bet=node:BetDAO(id = {betId}) "
    + "match (bet)-[:BET_ANSWER]->(betAnswer) "
    + "return bet, collect(betAnswer) as betAnswers")
BetWithInfo getByIdWithInfo(@Param("betId") String id);

我的投注信息对象：

import org.springframework.data.neo4j.annotation.QueryResult;
import org.springframework.data.neo4j.annotation.ResultColumn;
import fr.project.commons.data.graph.neo4j.beans.nodes.BetAnswerDAO;
import fr.project.commons.data.graph.neo4j.beans.nodes.BetDAO;
@QueryResult
public interface BetWithInfo {
    @ResultColumn("bet")
    BetDAO getBet();
    @ResultColumn("betAnswers")
    Iterable<BetAnswerDAO> getBetAnswers();
}

请求执行时没有错误，但是当我尝试访问投注答案集合时，出现以下错误：

Caused by: java.lang.RuntimeException: Cannot extract single value from Iterable with more than one elements.
    at org.springframework.data.neo4j.conversion.DefaultConverter.extractSingle(DefaultConverter.java:60)
    at org.springframework.data.neo4j.conversion.DefaultConverter.extractValue(DefaultConverter.java:51)
    at org.springframework.data.neo4j.conversion.DefaultConverter.convert(DefaultConverter.java:40)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.convert(EntityResultConverter.java:165)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.convert(QueryResultBuilder.java:103)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.access$300(QueryResultBuilder.java:81)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1$1.underlyingObjectToObject(QueryResultBuilder.java:121)
    at org.neo4j.helpers.collection.IteratorWrapper.next(IteratorWrapper.java:47)
    at org.neo4j.helpers.collection.IteratorUtil.addToCollection(IteratorUtil.java:403)
    at org.neo4j.helpers.collection.IteratorUtil.addToCollection(IteratorUtil.java:482)
    at org.neo4j.helpers.collection.IteratorUtil.asCollection(IteratorUtil.java:581)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.extractAndSetValueOfField(EntityResultConverter.java:129)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.extractPOJOResult(EntityResultConverter.java:102)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.convert(EntityResultConverter.java:163)
    at org.springframework.data.neo4j.conversion.DefaultConverter.convert(DefaultConverter.java:36)
    at org.springframework.data.neo4j.rest.SpringRestGraphDatabase$SpringResultConverter.convert(SpringRestGraphDatabase.java:148)
    at org.neo4j.rest.graphdb.util.QueryResultBuilder$1$1.underlyingObjectToObject(QueryResultBuilder.java:98)
    at org.neo4j.helpers.collection.IteratorWrapper.next(IteratorWrapper.java:47)
    at org.neo4j.helpers.collection.IteratorUtil.single(IteratorUtil.java:334)
    at org.neo4j.helpers.collection.IteratorUtil.singleOrNull(IteratorUtil.java:130)
    at org.neo4j.helpers.collection.IteratorUtil.singleOrNull(IteratorUtil.java:287)
    at org.springframework.data.neo4j.rest.SpringEndResult.singleOrNull(SpringEndResult.java:39)
    at org.springframework.data.neo4j.repository.query.GraphRepositoryQuery.dispatchQuery(GraphRepositoryQuery.java:115)
    at org.springframework.data.neo4j.repository.query.GraphRepositoryQuery$1.doWithGraph(GraphRepositoryQuery.java:86)
    at org.springframework.data.neo4j.support.Neo4jTemplate.doExecute(Neo4jTemplate.java:408)
    at org.springframework.data.neo4j.support.Neo4jTemplate.access$000(Neo4jTemplate.java:85)
    at org.springframework.data.neo4j.support.Neo4jTemplate$2.doInTransaction(Neo4jTemplate.java:422)
    at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
    at org.springframework.data.neo4j.support.Neo4jTemplate.exec(Neo4jTemplate.java:419)
    at org.springframework.data.neo4j.repository.query.GraphRepositoryQuery.execute(GraphRepositoryQuery.java:80)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:337)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
    ... 59 more

在我看来，我所做的与 spring-data 文档中的示例非常接近。我做错了什么？

编辑：我在代码中犯了一个错误。当getBetAnswers（）函数返回一个可迭代时，我收到此错误。使用集合，我收到以下错误：

java.lang.ClassCastException: org.springframework.data.neo4j.conversion.QueryResultBuilder$1 cannot be cast to java.util.Collection

Answer 1

你确定吗

@Query("start bet=node:BetDAO(id = {betId}) "
+ "match (bet)-[:BET_ANSWER]->(betAnswer) "
+ "return bet, collect(betAnswer) as betAnswers")
BetWithInfo getByIdWithInfo(@Param("betId") String id);

只返回 1 个结果？

据我了解，此查询在运行时返回几行，但 Spring Data 被告知仅返回 1 个 BetWithInfo。

仔细检查查询以确保它只返回 1 行，或者将方法返回类型从 BetWithInfo 迁移到 Iterable<BetWithInfo>（或Collection<BetWithInfo>）。

Answer 2

在BetWithInfo界面中，尝试更改

Collection<BetAnswerDAO> getBetAnswers();

自

Iterable<BetAnswerDAO> getBetAnswers();

Answer 3

我看起来像一个错误，如此处所述 谷歌论坛. 这将在下一个 spring-data-neo4j 版本中修复。它仍然存在于spring-data-neo4j 3.3.0.RELEASE。