如果后续 MATCH 失败，来自 WITH 的 Neo4j 值会消失

Question

我遇到了这个问题，我有一个使用 WITH 传递数据的密码

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
RETURN connected

这行得通。当KNOWS 关系创建时，connected 是true 否则false。因此，此密码返回 true 或 false。现在我想扩展这个

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
MATCH (x)-[zz:LIKES]->(y)    <------------- this match
WITH zz, connected
RETURN zz, connected

NOW connected 仅在标记匹配成功时返回 true 或 false。否则它会给出一个空的结果。无论MATCH 是否成功，我都希望connected 返回true 或false。

编辑：

抱歉，我在第二个查询中遗漏了一些内容。

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
MATCH (x)-[zz:LIKES]->(y)    <------------- this match
MERGE x-[:LOVES]->(y)        <------------- EDIT
WITH zz, connected
RETURN zz, connected

解决匹配问题时的可选匹配，它将失败并合并给出null 错误。有什么建议吗？

Answer 1

我认为这样的事情可能会奏效。

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
OPTIONAL MATCH (x)-[zz:LIKES]->(yy)
FOREACH(ignoreMe IN CASE WHEN yy IS null THEN [] ELSE [1] END |
    MERGE x-[:LOVES]->(yy))
WITH zz, connected
RETURN zz, connected

OPTIONAL MATCH 允许您保留所有初始行，然后如果没有关系，您将获得 'zz' 的空值。