SDN 4，Neo4j OGM @QueryResult Session.query 和 Pageable

Question

现在由于 Neo4j OGM 中有一个开放的 GitHub 问题 https://github.com/neo4j/neo4j-ogm/issues/215，我必须使用以下解决方法才能将返回 @QueryResult 的 org.neo4j.ogm.session.Session.query 结果转换为此 @QueryResult 的列表：

Cypher 查询示例：

 MATCH (parentD)-[:CONTAINS]->(childD:Decision)-[ru:CREATED_BY]->(u:User) WHERE id(parentD) = {decisionId}  OPTIONAL MATCH (childD)<-[:VOTED_FOR]-(vg:VoteGroup)-[:VOTED_ON]->(c:Criterion) WHERE id(c) IN {criteriaIds} WITH childD, ru, u, vg.avgVotesWeight as weight  OPTIONAL MATCH (childD)<-[:SET_FOR]->(sortValue375:Value)-[:SET_ON]->(sortCharacteristic375:Characteristic) WHERE id(sortCharacteristic375) = 375 RETURN childD AS decision, ru, u, toFloat(sum(weight)) as weight, sortValue375 ORDER BY weight DESC, sortValue375.value DESC, childD.createDate DESC SKIP 0 LIMIT 1000

解决方法：

@QueryResult
public class WeightedDecision {

    private Decision decision;

    private Double weight;

...
}

Result queryResult = session.query(characteristicCypher, parameters);

List<WeightedDecision> weightedDecisions = new ArrayList<>();

for (Map<String, Object> result : queryResult) {
    WeightedDecision weightedDecision = new WeightedDecision();
    weightedDecision.setDecision((Decision) result.get("decision"));
    weightedDecision.setWeight((double) result.get("weight"));
    weightedDecisions.add(weightedDecision);
}

现在我必须返回 Page<WeightedDecision> 而不是 List<WeightedDecision>

如何做到这一点？请帮我更改代码以便将 queryResult 转换为 Page<WeightedDecision>

另外，如何在这个逻辑中提供countQuery？

Answer 1

参考这篇文章Conversion of List to Page in Spring，您可以使用org.springframework.data.domain.PageImpl 实现从结果列表到Page 实例的映射。在您的情况下，将结果映射到 List 后，您可以执行以下操作：

PageRequest pageable = new PageRequest(0, 2);
Page<WeightedDecision> page = new PageImpl<>(weightedDecisions, pageable, weightedDecisions.size());

背景：据我所知，目前无法在 SDN (Paging and sorting in Spring Data Neo4j 4) 中的自定义查询上使用 Pageable。因此，您必须自己进行映射。

您的第二个问题与计数逻辑有关。在我看来，您必须第二次调用您的查询，并根据您要计算的内容进行更改。例如计算childD 节点：

MATCH (parentD)-[:CONTAINS]->(childD:Decision)-[ru:CREATED_BY]->(u:User) WHERE id(parentD) = {decisionId}  
OPTIONAL MATCH (childD)<-[:VOTED_FOR]-(vg:VoteGroup)-[:VOTED_ON]->(c:Criterion) WHERE id(c) IN {criteriaIds} WITH childD, ru, u, vg.avgVotesWeight as weight  
OPTIONAL MATCH (childD)<-[:SET_FOR]->(sortValue375:Value)-[:SET_ON]->(sortCharacteristic375:Characteristic) WHERE id(sortCharacteristic375) = 375 RETURN count(childD) AS result;