使用case语句在neo4j cypher中创建关系

Question

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.

Answer 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)
    )
)

Answer 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