neo4j - 如何在 Neo4j Cypher 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 子句根据 WHEN 结果运行不同的查询来优化我的 Neo4j 数据库调用和代码。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，但这是我想要实现的。我收到语法错误，例如无效输入“>”。我怎样才能以最好的方式实现这一目标？编辑可能的 APOC 解决方案：这是我在发现 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
}).....

有谁知道使用 apoc.do.when() 进行转换？请注意，我在第一个 THEN 中需要 'm' 和 'r'。

标签： neo4jcypher

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;