使用apoc.do.when时变量item未定义的问题排查求助

在使用Neo4j的apoc.do.when()过程中，出现错误：

Neo4jError: Failed to invoke procedure 'apoc.do.when': Caused by: org.neo4j.exceptions.SyntaxException: Variable 'item' not defined...

但condition参数中可正常访问item变量。item是从cart的JSON数组解码而来，已通过创建Item节点验证解码正常，但尝试将变量传入if/elseQuery时仍报错。

相关Cypher代码：

with apoc.convert.fromJsonMap($json) as order
create (o:Order) set o = order
with o, apoc.convert.fromJsonMap($request) as request
merge (u:User {uid: o.customerId})
merge (s:Shop {uid: o.shopId})
create (u)-[rel:MADE_ORDER]->(o)<-[rel1:RECEIVED_ORDER]-(s)
with o, u, s, request
unwind o.cart as jsonItems
with o, u, s, request, apoc.convert.fromJsonMap(jsonItems) as item
    
CALL apoc.do.when(
item.isPromotion = false,

'match (pr:Product {id: item.id}) 
set pr.soldQuantity = pr.soldQuantity + 1, 
pr.availableQuantity = pr.availableQuantity -1
create(u)-[:BOUGHT]->(pr)<-[:CONTAINS]-(o)
',

'match (p:Promotion {id: item.id})
set p.soldQuantity = pr.soldQuantity + 1, 
pr.availableQuantity = p.availableQuantity -1 
create(u)-[:BOUGHT]->(p)<-[:CONTAINS]-(o)'

,{})
YIELD value
return o as savedOrder

测试代码（创建Item节点可正常运行）：

with apoc.convert.fromJsonMap($json) as order
create (o:Order) set o = order
with o, apoc.convert.fromJsonMap($request) as request
merge (u:User {uid: o.customerId})
merge (s:Shop {uid: o.shopId})
create (u)-[rel:MADE_ORDER]->(o)<-[rel1:RECEIVED_ORDER]-(s)
with o, u, s, request
unwind o.cart as jsonItems
with o, u, s, request, apoc.convert.fromJsonMap(jsonItems) as item
create (i: Item) set i = item
return o as savedOrder

1. 变量未传入子查询
   apoc.do.when()的ifQuery和elseQuery是独立的子查询，外部的item、u、o变量不会自动传入，必须通过第四个参数（参数映射）显式传递。你当前第四个参数传的是空对象{}，导致子查询里找不到这些变量。

2. elseQuery中的变量笔误
   elseQuery里匹配的是p:Promotion，但更新时错误使用了ifQuery里的pr变量，应该统一用p来操作Promotion节点的属性。

修复后的代码：

with apoc.convert.fromJsonMap($json) as order
create (o:Order) set o = order
with o, apoc.convert.fromJsonMap($request) as request
merge (u:User {uid: o.customerId})
merge (s:Shop {uid: o.shopId})
create (u)-[rel:MADE_ORDER]->(o)<-[rel1:RECEIVED_ORDER]-(s)
with o, u, s, request
unwind o.cart as jsonItems
with o, u, s, request, apoc.convert.fromJsonMap(jsonItems) as item
    
CALL apoc.do.when(
item.isPromotion = false,

'match (pr:Product {id: $item.id}) 
set pr.soldQuantity = pr.soldQuantity + 1, 
pr.availableQuantity = pr.availableQuantity - 1
create($u)-[:BOUGHT]->(pr)<-[:CONTAINS]-($o)
',

'match (p:Promotion {id: $item.id})
set p.soldQuantity = p.soldQuantity + 1, 
p.availableQuantity = p.availableQuantity - 1 
create($u)-[:BOUGHT]->(p)<-[:CONTAINS]-($o)'

, {item: item, u: u, o: o})
YIELD value
return o as savedOrder

关键修改点：

• 在apoc.do.when()的第四个参数中，将外部变量item、u、o传入子查询，参数映射为{item: item, u: u, o: o}
• 子查询中使用$item、$u、$o来引用传入的参数
• 修正elseQuery中的变量错误，把pr改为p，确保更新的是Promotion节点的属性

内容的提问来源于stack exchange，提问作者Vincenzo