Cypher query with select first item from collect in neo4jclient

Question

I have the following code but I don't know how to do it in C# using the graphclient. It's the RETURN nodes[0] that confuses me.

What it does is that it will return all nodes and their properties with a distinct value of name.

PROFILE MATCH (t:Node { Mapped: true}) 
WITH t.name as t, collect(t) AS nodes
RETURN nodes[0]

Current implementation required me to get all and then use LINQ to get the distinct but this is slower:

 var res = graphClient.Cypher
                    .Match(match)
                    .Return(t => new
                    {
                        N = Return.As<string>("t.name")                       
                        LA = Return.As<double>("t.lat"),
                        LO = Return.As<double>("t.lon")
                    })
                    .OrderBy("t.name")
                    .Results;

//TODO: THE DISTINT NEEDS TO BE IN THE QUERY INSTEAD OF AFTER RESULT.
return res.Where(p => p.N != null).GroupBy(p => p.N).Select(grp => grp.FirstOrDefault());

Answer 1

You're probably going to want a proper result class instead of trying an anonymous type for this, so if you have this:

public class Location{
    [JsonProperty("name")]
    public string Name {get;set;}
    [JsonProperty("lat")]
    public double Lat { get; set; }
    [JsonProperty("lon")]
    public double Lon { get; set; }
}

You can then write the query as:

var query = client.Cypher
    .Match("(t:Node {Mapped: true})")
    .With("t.name AS t, collect(t) AS nodes")
    .Return(() => Return.As<Location>("nodes[0]"));

Which if you look at:

query.Query.DebugQueryText

You should see:

MATCH (t:Node {Mapped: true})
WITH collect(t) AS nodes
RETURN nodes[0]