如何在Neo4j cypher中的CASE WHEN THEN子句中执行密码查询

Question

我有一个用例，我试图通过使用Cypher中的RETURN case WHEN THEN子句来优化我的Neo4j数据库调用和代码，以根据WHEN结果运行不同的查询。这是我的例子：

MATCH (n {email: '[e-mail]'}) 
RETURN  
CASE WHEN n.category='Owner' THEN  MATCH '(n)-[r:OWNS]->(m)'  
WHEN n.category='Dealer' THEN MATCH (n)-[r:SUPPLY_PARTS_FOR]->(m) 
WHEN n.category='Mechanic' THEN MATCH (n)-[r:SERVICE]-(m) END 
AS result;

我不确定这是否合法，但这正是我想要实现的。我遇到语法错误，如无效输入'>'。我怎样才能以最好的方式做到这一点？编辑可能的APOC解决方案：这是我发现FOREACH的局限性之前的计划。。。

MATCH (user:Person {email:{paramEmail}})
FOREACH (_ IN case when 'Owner' = {paramCategory} then [1] else [] end|
SET user:Owner, user += queryObj 
WITH user, {paramVehicles} AS coll
UNWIND coll AS vehicle
MATCH(v:Vehicles {name:vehicle}) 
CREATE UNIQUE (user)-[r:OWNS {since: timestamp()}]->(v)
SET r += paramVehicleProps 
)
FOREACH (_ IN case when 'Mechanic' = {Category} then [1] else [] end|
SET user:Owner, user += queryObj 
WITH user, {paramVehicles} AS coll
….
)
FOREACH (_ IN case when 'Dealer' = {paramCategory} then [1] else [] end|
SET user:Owner, user += queryObj 
WITH user, {paramVehicles} AS coll
…...
)
RETURN user,
CASE {paramCategory}
WHEN 'Owner' THEN [(n)-[r:OWNS]->(m) | m and r]
WHEN 'Dealer' THEN [(n)-[r:SUPPLY_PARTS_FOR]->(m) | m] 
WHEN 'Mechanic' THEN [(n)-[r:SERVICE]-(m) | m]
END AS result`,{
paramQueryObj: queryObj,
paramVehicles: makeVehicleArray,
paramVehicleProps: vehiclePropsArray,
paramSalesAgent: dealerSalesAgentObjarray,
paramWarehouseAgent: dealerWarehouseAgentObjarray
}).....

有人知道用apoc.do.when((转换吗？注意，我需要在第一个THEN中使用'm'和'r'。

Answer 1

您仍然应该在第一次匹配中使用标签，否则您将获得完整的数据库扫描，而不是通过电子邮件进行索引查找！！

对于您的查询，您可以使用模式理解：

MATCH (n:Person {email: '[e-mail]'}) 
RETURN  
CASE n.category 
WHEN 'Owner'    THEN  [(n)-[r:OWNS]->(m) | m]
WHEN 'Dealer'   THEN [(n)-[r:SUPPLY_PARTS_FOR]->(m) | m] 
WHEN 'Mechanic' THEN [(n)-[r:SERVICE]-(m) | m] END 
AS result;

Answer 2

也可以使用apoc.do.case：https://neo4j.com/labs/apoc/4.4/overview/apoc.do/apoc.do.case/

CALL apoc.do.case([
false,
'CREATE (a:Node{name:"A"}) RETURN a AS node',
true,
'CREATE (b:Node{name:"B"}) RETURN b AS node'
],
'CREATE (c:Node{name:"C"}) RETURN c AS node',{})
YIELD value
RETURN value.node AS node;