Issue utilizing OrderBy With Neo4jClient - cypher

Question

I'm sorting a large database by the quantity of outgoing relationships. I have a working Cypher query as follows:
optional match (n)-[r]->(m)
return n, Count(r) as c
order by c DESC limit 1;
The Cypher query is working as anticipated. However, as I am debugging and stepping through the Cypher -> Neo4jClient conversion, I cannot seem to find the root of the issue.
public ReturnPayload[] getByConnections()
{
var query = client.Cypher
.OptionalMatch("(p)-[r]->(m)")
.Return((p, r, m, c) => new
{
p = p.As<Person>(),
pid = (int)p.Id(),
e = r.As<RelationshipInstance<Object>>(),
m = m.As<Metadata>(),
c = r.Count()
}).OrderByDescending("c").Limit(1);
var res = query.Results;
var payload = new List<ReturnPayload>();
foreach (var el in res)
{
var t = new ReturnPayload();
t.e = el.e;
t.m = el.m;
t.pid = el.pid;
t.p = el.p;
payload.Add(t);
}
return payload.ToArray<ReturnPayload>();
}
I suspect that a part of the problem may be that I am not utilizing CollectAs<T>() and thus it is referring a count of '1' per each person. Unfortunately, I have attempted using CollectAs<T>() and CollectAsDisctinct<T>() and my resultant JSON architecture is only wrapping each individual element in an array, as opposed to aggregating identical elements into an array proper.
The FOREACH loop is there to assist in converting from the anonymous type into my relatively standard <ReturnPayload> which does not utilize a c object within its parameters.
Your time is appreciated, thank you.
Debugged Query Test:
OPTIONAL MATCH (p)-[r]->(m)
RETURN p AS p, id(p) AS pid, r AS e, m AS m, count(r) AS c
ORDER BY c DESC
LIMIT {p0}
And my 'functional' Cypher query:
optional match (n)-[r]->(m)
return n, Count(r) as c
order by c DESC limit 1;

Answer 1

So, you've identified yourself that you're running two different queries. This is the issue: your C# does not match the Cypher you're expecting.
To make the C# match the working Cypher, change it to this:
var query = client.Cypher
.OptionalMatch("(n)-[r]->(m)")
.Return((n, r) => new
{
n = n.As<Person>(),
c = r.Count()
})
.OrderByDescending("c")
.Limit(1);
That should now produce the same query, and thus the same output as you're expecting from the working Cypher.
On a purely stylistic note, you can also simplify your foreach query to a more functional equivalent:
var payload = query
.Results
.Select(r => new ReturnPayload {
n = r.n,
c = r.c
})
.ToArray();
return payload;
However, as I look closer as your query, it looks like you just want the count for the sake of getting the top 1, then you're throwing it away.
Consider using the WITH clause:
optional match (n)-[r]->(m)
with n as n, count(r) as c
order by c desc
limit 1
return n
You can map that back to C# using similar syntax:
var query = client.Cypher
.OptionalMatch("(n)-[r]->(m)")
.With((n, r) => new
{
n = n.As<Person>(),
c = r.Count()
})
.OrderByDescending("c")
.Limit(1)
.Return(n => new ReturnPayload // <-- Introduce the type here too
{
n = n.As<Person>()
});
Then, you don't need to query for data and just throw it away with another foreach loop. (You'll notice I introduce the DTO type in the Return call as well, so you don't have to translate it out of the anonymous type either.)
(Disclaimer: I'm just typing all of this C# straight into the answer; I haven't double checked the compilation, so my signatures might be slightly off.)
Hope that helps!