Neo4j SDN4 实体继承和索引

Question

我有以下 Cypher 查询：

PROFILE MATCH (childD:Decision)
WITH childD
ORDER BY childD.createDate 
DESC SKIP 0 LIMIT 10 
MATCH (childD:Decision)-[ru:CREATED_BY]->(u:User) 
OPTIONAL MATCH (childD:Decision)-[rup:UPDATED_BY]->(up:User) 
RETURN ru, u, rup, up, childD AS decision, [ (childD)-[rdt:BELONGS_TO]->(t:Tag) | t ] AS tags

现在在我的 Neo4j 数据库（~23k 决策节点）上这个查询工作了~50 毫秒，我不明白或者它在 childD.createDate 字段上使用索引。

这是PROFILE输出：

这是我的 SDN 4 实体：

@NodeEntity
public abstract class BaseEntity implements BaseEntityVisitable {

    private static final String CREATED_BY = "CREATED_BY";
    private static final String UPDATED_BY = "UPDATED_BY";

    @GraphId
    private Long graphId;

    @Index(unique = false)
    private Date createDate;

    @Relationship(type = CREATED_BY, direction = Relationship.OUTGOING)
    private User createUser;

    @Index(unique = false)
    private Date updateDate;

    @Relationship(type = UPDATED_BY, direction = Relationship.OUTGOING)
    private User updateUser;

....

}

@NodeEntity
public class Decision extends BaseEntity {

    private static final String BELONGS_TO = "BELONGS_TO";
    private static final String CONTAINS = "CONTAINS";
    private static final String DEFINED_BY = "DEFINED_BY";

    @Index(unique = true)
    private Long id;

    @Index(unique = false)
    private String name;

....

}

这是:schema输出：

Indexes
   ON :BaseEntity(createDate) ONLINE 
   ON :BaseEntity(updateDate) ONLINE 

   ON :Decision(lowerName) ONLINE 
   ON :Decision(name) ONLINE 
   ON :Decision(totalChildDecisions) ONLINE 
   ON :Decision(totalViews) ONLINE 

   ON :Decision(id) ONLINE  (for uniqueness constraint)

请注意 createDate 索引设置在 :BaseEntity 而不是 :Decision

检查此索引是否适用于（或无效）这部分查询的热门话题：ORDER BY childD.createDate

Answer 1

我认为您混淆了索引和 排序顺序 。这个查询没有任何理由使用索引，因为你没有给它任何值来搜索索引。可能是索引实现按顺序排列了日期，但没有规定必须如此（显然查询没有使用索引对决策节点进行排序）。

希望对您有所帮助。

此致，汤姆

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