Cypher查询丢失Employment键值对问题及解决方法咨询

问题场景 #

我编写了如下Cypher查询：

WITH {} as ceNodeIds 
WITH ceNodeIds {`Employment`: [6, 7, 8]} 
WITH ceNodeIds  
MATCH (root3:Location ) 
WHERE root3.id IN ([1, 2, 3]) 
WITH ceNodeIds, root3 OPTIONAL 
MATCH (root3)-[:CONTAINS*0..]->(descendant3:Location) 
OPTIONAL MATCH (ascendant3:Location)-[:CONTAINS*0..]->(root3) 
WITH ceNodeIds, COLLECT(root3.id) AS listRoot3, COLLECT( DISTINCT ascendant3.id) AS listAscendant3, COLLECT( DISTINCT descendant3.id) AS listDescendant3 
WITH ceNodeIds {`Location`: apoc.coll.union(listDescendant3, apoc.coll.union(listRoot3, listAscendant3))}  
WITH ceNodeIds 
RETURN ceNodeIds 

预期返回包含两个键值对的Map对象：

"Employment": [6, 7, 8]
"Location": [1, 2, 3, 4, 5]

但实际仅返回：

"Location": [1, 2, 3, 4, 5]

原因分析 #

Employment键值对丢失的核心原因是：

• Cypher中ceNodeIds {Location: ...}的语法是创建全新的Map对象，而非在原Map上追加键值。这行代码会完全丢弃原ceNodeIds中的所有已有键（包括Employment），仅保留新定义的Location键，导致之前的Employment数据被覆盖。

正确实现方式 #

要保留原Map的所有键并新增Location，需使用Map合并运算符+，将原Map与新键的Map合并。修改后的查询如下：

WITH {} as ceNodeIds 
WITH ceNodeIds {`Employment`: [6, 7, 8]} 
WITH ceNodeIds  
MATCH (root3:Location ) 
WHERE root3.id IN ([1, 2, 3]) 
WITH ceNodeIds, root3 
OPTIONAL MATCH (root3)-[:CONTAINS*0..]->(descendant3:Location) 
OPTIONAL MATCH (ascendant3:Location)-[:CONTAINS*0..]->(root3) 
WITH ceNodeIds, COLLECT(root3.id) AS listRoot3, COLLECT(DISTINCT ascendant3.id) AS listAscendant3, COLLECT(DISTINCT descendant3.id) AS listDescendant3 
-- 用+合并原Map与新键，保留原有Employment
WITH ceNodeIds + {`Location`: apoc.coll.union(listDescendant3, apoc.coll.union(listRoot3, listAscendant3))} AS ceNodeIds  
RETURN ceNodeIds 

另外，原查询中WITH ceNodeIds, root3 OPTIONAL的写法存在语法歧义，建议将OPTIONAL单独放在MATCH前，避免解析错误。

内容的提问来源于stack exchange，提问作者alexanoid