【问题标题】：How do I return relationship properties (Neo4j + Spring data)?如何返回关系属性（Neo4j + Spring 数据）？
【发布时间】：2021-04-16 13:23:54
【问题描述】：

项目详情

我正在使用 Kotlin 关注这些文档 Spring Data Neo4j，我正在努力从存储库查询中返回关系：

数据库布局

我有一个User 节点和一个Skill 节点，关系如下：

实体

技能

@Node
data class Skill(
        @Id
        val uid: UUID,

        val title: String,
) {

    constructor(title: String) : this(UidGenerator.makeOne(), title)

}

用户

@Node
data class User(
        @Id
        var uid: UUID,

        @Relationship(type = "DEMONSTRATES")
        val demonstrates: List<Demonstrates>,

        val firstName: String,
        val lastName: String,
) {

    constructor(demonstrates: List<Demonstrates>, firstName: String, lastName: String)
            : this(UidGenerator.makeOne(), demonstrates, firstName, lastName)

}

关系属性

@RelationshipProperties
data class Demonstrates(
        @TargetNode
        val skill: Skill,

        val rating: Int,
)

我遇到的问题

当我注入以下存储库并调用 getDemonstrationList 时，我收到以下错误。

@Repository
interface MyRepository : Neo4jRepository<Skill, UUID> {

    @Query("""
        MATCH (:User)-[d:DEMONSTRATES]->(:Skill) RETURN d
    """)
    fun getDemonstrationList(): List<Demonstrates>

}

Caused by: org.springframework.data.neo4j.core.mapping.NoRootNodeMappingException: Could not find mappable nodes or relationships inside Record<{d: relationship<4>}> for org.springframework.data.neo4j.core.mapping.DefaultNeo4jPersistentEntity@750a04ec
    at org.springframework.data.neo4j.core.mapping.DefaultNeo4jEntityConverter.read(DefaultNeo4jEntityConverter.java:106) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.mapping.DefaultNeo4jEntityConverter.read(DefaultNeo4jEntityConverter.java:67) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.mapping.Schema.lambda$getRequiredMappingFunctionFor$0(Schema.java:96) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.repository.query.Neo4jQuerySupport.lambda$getMappingFunction$0(Neo4jQuerySupport.java:105) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.PreparedQuery$AggregatingMappingFunction.apply(PreparedQuery.java:218) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.PreparedQuery$AggregatingMappingFunction.apply(PreparedQuery.java:154) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.DelegatingMappingFunctionWithNullCheck.apply(DelegatingMappingFunctionWithNullCheck.java:45) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.DelegatingMappingFunctionWithNullCheck.apply(DelegatingMappingFunctionWithNullCheck.java:35) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.DefaultNeo4jClient$DefaultRecordFetchSpec.lambda$partialMappingFunction$0(DefaultNeo4jClient.java:325) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) ~[na:na]
    at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133) ~[na:na]
    at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[na:na]
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) ~[na:na]
    at org.springframework.data.neo4j.core.DefaultNeo4jClient$DefaultRecordFetchSpec.all(DefaultNeo4jClient.java:312) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.core.Neo4jTemplate$DefaultExecutableQuery.getResults(Neo4jTemplate.java:575) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.repository.query.Neo4jQueryExecution$DefaultQueryExecution.execute(Neo4jQueryExecution.java:51) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.neo4j.repository.query.AbstractNeo4jQuery.execute(AbstractNeo4jQuery.java:85) ~[spring-data-neo4j-6.0.2.jar:6.0.2]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:152) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:131) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.2.jar:5.3.2]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.2.jar:5.3.2]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.2.jar:5.3.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.2.jar:5.3.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.data.repository.core.support.MethodInvocationValidator.invoke(MethodInvocationValidator.java:98) ~[spring-data-commons-2.4.2.jar:2.4.2]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.2.jar:5.3.2]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.2.jar:5.3.2]
    at com.sun.proxy.$Proxy68.getDemonstrationIds(Unknown Source) ~[na:na]
    at com.ntr.neo4j.Neo4jApplication.run(Neo4jApplication.kt:44) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:804) ~[spring-boot-2.4.1.jar:2.4.1]
    ... 5 common frames omitted

我的问题

我对 Kotlin 和 Neo4j 还很陌生，但我确实了解 Spring 框架。据我了解，存储库无法确定它需要从我的查询结果中创建一个Demonstrates 实例列表。我有兴趣让rating 属性脱离关系，但教程并不清楚我该如何做到这一点。请让我知道我缺少什么以便让我的查询返回Demonstrates 的列表？

【问题讨论】：

标签： java kotlin neo4j spring-data spring-data-neo4j

【解决方案1】：

从 Spring Data Neo4j 6 开始，关系不再是顶级实体。

因此，您的存储库方法必须返回Skill、SomeCollection<Skill>（其中SomeCollection 可以是List、Set、Flux、Page 等）。您还可以返回基于 Skill 的投影，但不能返回 @RelationshipProperties-annotated 类。

【讨论】：