create relationships in neo4j cypher using case statement

问题

I have a JSON in the next form:

{ "conditions": [ { "id": "123", "type": "a", entities: ["529", "454"] },
                  { "id": "124", "type": "b", entities: ["530", "455"] }
  ]
}

I want to create relation ship between the Condition node with node A Entities or node B entities based on type attribute which can be A/B i Assuming that these entities already exists in neo4j.

I am trying something like the below cypher but that doesn't work.

WITH {json} as data
UNWIND data.conditions as condition 
MATCH (c:Condition { conditionId: condition.id})
CASE c.type 
    WHEN 'a' THEN FOREACH (sid IN condition.entities | 
        MERGE (s:NodeA {nr_serverId:sid}) MERGE (s)-[:ATTACHED_TO]->(c)
    )
    WHEN 'b' THEN FOREACH (aid IN condition.entities | 
       MERGE (a:NodeB {nr_appId: aid}) MERGE (a)-[:ATTACHED_TO]->(c)
    )
END;

Can anyone please help me with the correct way of doing this? Thank you.

回答1:

Since at the moment there is no classical conditional statements in cypher, you can use the famous trick with foreach and case:

WITH {json} as data
UNWIND data.conditions as condition 
MATCH (c:Condition { conditionId: condition.id})
FOREACH (ift in CASE WHEN c.type = 'a' THEN [1] ELSE [] END |
    FOREACH (sid IN condition.entities | 
        MERGE (s:NodeA {nr_serverId:sid}) MERGE (s)-[:ATTACHED_TO]->(c)
    )
)
FOREACH (ift in CASE WHEN c.type = 'b' THEN [1] ELSE [] END |
    FOREACH (aid IN condition.entities | 
       MERGE (a:NodeB {nr_appId: aid}) MERGE (a)-[:ATTACHED_TO]->(c)
    )
)

回答2:

APOC Procedures just updated with support for conditional cypher execution. You'll need version 3.1.3.7 or greater (if using Neo4j 3.1.x), or version 3.2.0.3 or greater (if using Neo4j 3.2.x).

Here's an example of using these new procedures to execute your query:

WITH {json} as data
UNWIND data.conditions as condition 
MATCH (c:Condition { conditionId: condition.id})
CALL apoc.do.case([
  c.type = 'a', 
   "FOREACH (sid IN condition.entities | 
        MERGE (s:NodeA {nr_serverId:sid}) MERGE (s)-[:ATTACHED_TO]->(c))",
  c.type = 'b',
   "FOREACH (aid IN condition.entities | 
       MERGE (a:NodeB {nr_appId: aid}) MERGE (a)-[:ATTACHED_TO]->(c))"
], '', {condition:condition, c:c}) YIELD value

来源：https://stackoverflow.com/questions/43010726/create-relationships-in-neo4j-cypher-using-case-statement

标签

neo4j

switch-statement

cypher