如何在Neo4j中对两个节点之间的关系数量创建约束

Question

我想创建一个这样的约束：

create constraint on (a:NodeTypeA)-[r:TYPE_OF_REL]->(b:NodeTypeB) ASSERT count(r) < 2

Answer 1

You can kind of get the same result by using MERGE instead of CREATE whenever you create such a relationship. For example:

MATCH (a:NodeTypeA {id: 123}), (b:NodeTypeB {id: 456})
MERGE (a)-[r:TYPE_OF_REL]->(b);

The MERGE will not create the relationship if it already exists.

(Note, however, that duplicate relationships are still possible if multiple MERGE operations can run concurrently. This is not a concern if you are using a neo4j 3.1.2 or later, or the DB is only asked to perform one operation at a time.)

Answer 2

根据文档 ，Neo不支持此功能。