如何在单个语句中减去 Neo4j 中不同条件的相同返回值

Question

我正在使用 Java 来匹配我这样的语句。

Result firstResult = db.execute("MATCH (n)-[:someRelation]->(m) WHERE n.name='firstN' RETURN m.cal");
Result secondResult = db.execute("MATCH (n)-[:someRelation]->(m) WHERE n.name='Second' RETURN m.cal");

那么如何在一次匹配中减去这两个语句而无需创建另一个 Result (secondResult) ？

Answer 1

如果您将每个都放在一个集合中，然后过滤掉一个集合中不在另一个集合中的那些，您将有效地从另一个中减去一个。

// put the result of the first set in a collection
MATCH (n)-[:someRelation]->(m) 
WHERE n.name='firstN' 
WITH collect(m.cal) as m_cal_coll_1
//
// put the second set in a collection
MATCH (n)-[:someRelation]->(m) 
WHERE n.name='Second'
WITH m_cal_coll_1, collect(m.cal) as m_cal_coll_2
//
// return items in the first that are not in the second
return filter(x IN m_cal_coll_1 WHERE not x in m_cal_coll_2 )