CODEWITHSUNDEEP
neo4jcypher
Matthias
Matthias

Reputation: 12259

Order nodes by relationship count --> ThisShouldNotHappenError

In a Neo4j database with a couple of nodes and relationships, I am trying to find out the most "popular" users (in this case: The nodes participating in most relationships):

START n=node:user('*:*')
MATCH (n)-[r]->(x)
RETURN n
ORDER BY COUNT(r) DESC
LIMIT 10

However, this query (Neo4j 1.9.2) results in the following error:

ThisShouldNotHappenError

Developer: Andres claims that: Aggregations should not be used like this.

StackTrace: org.neo4j.cypher.internal.commands.expressions.AggregationExpression.apply(AggregationExpression.scala:31) org.neo4j.cypher.internal.commands.expressions.AggregationExpression.apply(AggregationExpression.scala:29) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1$$anonfun$apply$1.apply(ExtractPipe.scala:47) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1$$anonfun$apply$1.apply(ExtractPipe.scala:45) scala.collection.immutable.Map$Map1.foreach(Map.scala:109) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1.apply(ExtractPipe.scala:45) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1.apply(ExtractPipe.scala:44) scala.collection.Iterator$$anon$11.next(Iterator.scala:328) org.neo4j.cypher.internal.pipes.TopPipe.internalCreateResults(TopPipe.scala:45) org.neo4j.cypher.internal.pipes.PipeWithSource.createResults(Pipe.scala:69) org.neo4j.cypher.internal.pipes.PipeWithSource.createResults(Pipe.scala:66) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl.org$neo4j$cypher$internal$executionplan$ExecutionPlanImpl$$prepareStateAndResult(ExecutionPlanImpl.scala:164) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl$$anonfun$getLazyReadonlyQuery$1.apply(ExecutionPlanImpl.scala:139) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl$$anonfun$getLazyReadonlyQuery$1.apply(ExecutionPlanImpl.scala:138) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl.execute(ExecutionPlanImpl.scala:38) org.neo4j.cypher.ExecutionEngine.execute(ExecutionEngine.scala:72) org.neo4j.cypher.ExecutionEngine.execute(ExecutionEngine.scala:76) org.neo4j.cypher.javacompat.ExecutionEngine.execute(ExecutionEngine.java:79) org.neo4j.server.rest.web.CypherService.cypher(CypherService.java:94) java.lang.reflect.Method.invoke(Method.java:611) org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)

Any ideas on how I can express this differntly?

Upvotes: 14

Views: 13707

Answers (2)

Lisa Li
Lisa Li

Reputation: 2592

In terms of neo4j mannual, if you need to use an aggregration in your "Order by", you must include the aggregration in your "Return", so you just need to add the count(r) in your "Return" as shown below, 

START n=node:user('*:*')
MATCH (n)-[r]->(x)
RETURN n, COUNT(r)
ORDER BY COUNT(r) DESC
LIMIT 10

Upvotes: 23

Stefan Armbruster
Stefan Armbruster

Reputation: 39915

Introduce a WITH here:

START n=node:user('*:*')
MATCH (n)-[r]->()
WITH n, count(r) as c
RETURN n, c
ORDER BY c DESC
LIMIT 10

Upvotes: 5

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