Ordering By Relationship Property Using Neo4jClient C#

Question

I want to get the following query in its C# equivalent:

match(p:Person)-[r1:HAS]->(s:Shelf) 
optional match(s)-[r2:CONTAINS]->(l:Link) return p,s,l 
order by r2.time_modified;

I initially thought about this but it doesn't work:

var result = await this._graphClient.Cypher
                 .Match("(person:Person { person_id: {personId}})-[r1:HAS]->(shelf:Shelf)")
                 .OptionalMatch("(shelf)-[r2:CONTAINS]->(link:Link)")
                 .WithParams(new { personId = personId })
                 .Return((shelf, link) => new 
                  {
                     Shelf = shelf.As<Shelf>(),
                     Links = link.CollectAs<Link>()
                  })
                 .OrderBy("r2.time_modified")
                 .ResultsAsync;

I get the following exception that r2 isn't defined

r2 not defined ... "ORDER BY r2.time_modified"

I am relatively new to using the Neo4jClient C# driver. Can anyone please help me and explain to me what's happening? I also want to know how to pull this off.

This is the stack trace:

at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions) at System.Threading.Tasks.Task1.GetResultCore(Boolean waitCompletionNotification) at System.Threading.Tasks.Task1.get_Result() at Neo4jClient.GraphClient.<>c__851.<PrepareCypherRequest>b__85_1(Task1 response) in D:\temp\d298ce3\Neo4jClient\GraphClient.cs:line 961 at System.Threading.Tasks.ContinuationResultTaskFromResultTask2.InnerInvoke() at System.Threading.Tasks.Task.Execute() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.ConfiguredTaskAwaitable1.ConfiguredTaskAwaiter.GetResult() at Neo4jClient.GraphClient.d__871.MoveNext() in D:\temp\d298ce3\Neo4jClient\GraphClient.cs:line 1022 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter1.GetResult() at ....Repository.Neo4jRepository.d__23.MoveNext() in C:\Users\Williams\documents\visual studio 2015\Projects...\Repository\Neo4jRepository.cs:line 358

What type is the exception? Where is it coming from? i.e. is it the client or Neo4j returning it? — Charlotte Skardon, Mar 30 '16 at 10:57
I think it's from the client cos i wrote the same thing in Neo4j and it worked but the client returns the exception — Williams Adu, Mar 30 '16 at 11:12
What type is the Exception - where is it thrown from, you can also paste more of the content of the exception here — Charlotte Skardon, Mar 30 '16 at 11:13
The exception name is SyntaxException, the source is Neo4jClient and the NeoMessage is "r2 not defined (line 4, column 10 (offset: 179)) "ORDER BY r2.time_modified" ^ — Williams Adu, Mar 30 '16 at 11:23
OK, I have it replicating - the error comes from Neo4j not from the client, so let's try to see why this works via the browser, but not the API — Charlotte Skardon, Mar 30 '16 at 13:14

score 2 · Accepted Answer · answered Mar 30 '16 at 13:37

2

Because you do the Collect in the Return statment, r2 doesn't exist anymore.

You need to order before returning:

var query = gc.Cypher
    .Match("(p:Person { person_id: 'a'})-[r1:HAS]->(s:Shelf)")
    .OptionalMatch("(s)-[r2:CONTAINS]->(l:Link)")
    .With("p,s,l")
    .OrderBy("r2.time_modified")
    .Return((p,s,l) => new
    {
         Person = p.As<Person>(),
         Shelf = s.As<Shelf>(),
         Links = l.CollectAs<Link>()
    });
var res = query.Results;

answered Mar 30 '16 at 13:37

Charlotte Skardon

6,220
2
31
42

What is the purpose of 'with' please? Why doesn't it contain 'r1' and 'r2'? – Williams Adu Mar 30 '16 at 13:46
This is one of the best i've seen regarding this question. Thanks for your input Chris. – Willie Mar 30 '16 at 14:24
Think of `With` as a kind of 'combiner' of queries, it's used quite often when you want to combine lots of queries together. Kind of like a `Return` in the middle of your query - where you can then use that `Return` in the next query and so on and so on - here's the docs on it: http://neo4j.com/docs/stable/query-with.html – Charlotte Skardon Mar 30 '16 at 14:49

erdelmaero · Answer 2 · 2016-03-30T10:23:25.177

1

You need to RETURN r2.time_modified before you can order results by it.

match(p:Person)-[r1:HAS]->(s:Shelf) 
optional match(s)-[r2:CONTAINS]->(l:Link) 
return p,s,l,r2.time_modified
order by r2.time_modified;

If it is returned you can use it for ORDER BY.

[EDIT]

Untested:

var result = await this._graphClient.Cypher
                 .Match("(person:Person { person_id: {personId}})-[r1:HAS]->(shelf:Shelf)")
                 .OptionalMatch("(shelf)-[r2:CONTAINS]->(link:Link)")
                 .WithParams(new { personId = personId })
                 .Return((shelf, link, r2) => new 
                  {
                     Shelf = shelf.As<Shelf>(),
                     Links = link.CollectAs<Link>()
                  })
                 .OrderBy("r2.time_modified")
                 .ResultsAsync;

edited Mar 30 '16 at 10:23

answered Mar 30 '16 at 10:05

erdelmaero

43
8

I get it so how do i get it's C# equivalent? Can you add it to your answer for my examination? – Williams Adu Mar 30 '16 at 10:20
I just tested it but i had an exception. The truth is that i haven't created that property on all the relationships. That's why i use "Optional Match". I still get the same exception that "r2" is not defined. Is there a way to order just in case its available and ignore if it isn't there? – Williams Adu Mar 30 '16 at 10:30
It should work even if some of the propertys are NULL. Maybe you check this post: http://stackoverflow.com/questions/16558103/incorrect-sort-order-with-neo4jclient-cypher-query – erdelmaero Mar 30 '16 at 10:39

Ordering By Relationship Property Using Neo4jClient C#

2 Answers2