performance - 在 Neo4j 中使用 FOREACH 时删除关系

Question

我需要删除在 FOREACH 上迭代的节点的特定类型的关系。

详细::

PROFILE MATCH (n:Label1)-[r1:REL1]-(a:Label2) 
WHERE a.prop1 = 2 
WITH n 
WITH COLLECT(n) AS rows 
WITH [a IN rows WHERE a.prop2 < 1484764200] AS less_than_rows, 
[b IN rows WHERE b.prop2 = 1484764200 AND b.prop3 < 2] AS other_rows 
WITH size(less_than_rows) + size(other_rows) AS count, less_than_rows, other_rows
FOREACH (sub IN less_than_rows | 
  MERGE (sub)-[r:REL2]-(:Label2) 
  DELETE r 
  MERGE(l2:Label2{id:540}) 
  MERGE (sub)-[:APPEND_TO {s:0}]->(l2) 
  SET sub.prop3=1, sub.prop2=1484764200) 
WITH DISTINCT other_rows, count 
FOREACH (sub IN other_rows | 
  MERGE(l2:Label2{id:540}) 
  MERGE (sub)-[:APPEND_TO {s:0}]->(l2) 
  SET sub.prop3=sub.prop3+1)
RETURN count

由于 FOREACH 不支持 MATCH，我使用 MERGE 来实现它。但是当我执行它时它很慢(大约需要 1 分钟)。
但是如果我在没有 FOREACH(停止更新)的情况下执行，它会给出大约 1 秒的时间。

问题::显然是 FOREACH 或在 FOREACH 中的内部操作的问题。
我想删除一个特定的关系，创建另一个关系并将一些属性设置为节点。

注意::我显示了总查询，因为有没有其他方法可以实现相同的要求(在此 FOREACH 之外，我尝试使用 CASE WHEN)

Answer 1

我注意到有关您的原始查询的一些信息:

MERGE(l2:Label2 {id:540})应该从 FOREACH 中移出条款，因为它只需要做一次。这会减慢查询速度。事实上，如果你希望节点已经存在，你可以使用 MATCH反而。

MERGE (sub)-[:APPEND_TO {s:0}]->(l2)可能不会按照您的意愿行事，因为它只会匹配 s 的现有关系。属性(property)还在0 .如 s不是 0 ，您最终将创建一个额外的关系。确保有一个单一的关系并且它的 s值是(重置为)0 ，您应该删除 {s:0}从模式测试并使用 SET设置 s值(value);这也应该加快MERGE ，因为它不需要进行属性值测试。

这个版本的查询应该可以解决上述问题，并且速度会更快(但您必须尝试一下，看看能快多少):

PROFILE
MATCH (n:Label1)-[:REL1]-(a:Label2)
WHERE a.prop1 = 2
WITH COLLECT(n) AS rows
WITH
  [a IN rows WHERE a.prop2 < 1484764200] AS less_than_rows, 
  [b IN rows WHERE b.prop2 = 1484764200 AND b.prop3 < 2] AS other_rows 
WITH size(less_than_rows) + size(other_rows) AS count, less_than_rows, other_rows
MERGE(l2:Label2 {id:540}) 
FOREACH (sub IN less_than_rows | 
  MERGE (sub)-[r:REL2]-(:Label2) 
  DELETE r 
  MERGE (sub)-[r2:APPEND_TO]->(l2)
  SET r2.s = 0, sub.prop3 = 1, sub.prop2 = 1484764200) 
WITH DISTINCT l2, other_rows, count 
FOREACH (sub IN other_rows | 
  MERGE (sub)-[r3:APPEND_TO]->(l2) 
  SET r3.s = 0, sub.prop3 = sub.prop3+1)
RETURN count;

如果您只想设置 s当 APPEND_TO 时值为 0正在创建关系，然后使用 ON CREATE条款而不是 SET :

PROFILE
MATCH (n:Label1)-[:REL1]-(a:Label2)
WHERE a.prop1 = 2
WITH COLLECT(n) AS rows
WITH
  [a IN rows WHERE a.prop2 < 1484764200] AS less_than_rows, 
  [b IN rows WHERE b.prop2 = 1484764200 AND b.prop3 < 2] AS other_rows 
WITH size(less_than_rows) + size(other_rows) AS count, less_than_rows, other_rows
MERGE(l2:Label2 {id:540}) 
FOREACH (sub IN less_than_rows | 
  MERGE (sub)-[r:REL2]-(:Label2) 
  DELETE r 
  MERGE (sub)-[r2:APPEND_TO]->(l2)
  ON CREATE SET r2.s = 0
  SET sub.prop3 = 1, sub.prop2 = 1484764200) 
WITH DISTINCT l2, other_rows, count 
FOREACH (sub IN other_rows | 
  MERGE (sub)-[r3:APPEND_TO]->(l2)
  ON CREATE r3.s = 0
  SET sub.prop3 = sub.prop3+1)
RETURN count;