Returning composite class with Neo4jClient

Question

The Neop4jClient cypher wiki (https://github.com/Readify/Neo4jClient/wiki/cypher) contains an example of using lambda expressions to return multiple projections...

var query = client
.Cypher
.Start(new { root = client.RootNode })
.Match("root-[:HAS_BOOK]->book-[:PUBLISHED_BY]->publisher")
.Return((book, publisher) => new {
    Book = book.As<Book>(),
    Publisher = publisher.As<Publisher>(),
});

So the query will return details of both book nodes and publisher nodes. But I want to do something slightly different. I want to combine the contents of a single node type with a property of the matched path. Lets say I have Person nodes with a property 'name', and a class defined so,,,

public class descendant
{
    public string name { get; set; }
    public int depth { get; set; }
}

A cypher query like this will return what I want, which is all descendants of a given node with the depth of the relationship...

match p=(n:Person)<-[*]-(child:Person) 
where n.name='George' 
return distinct child.name as name, length(p) as depth

If I try a Neo4jClient query like this...

var query =
     _graphClient.Cypher
          .Match("p=(n:Person)<-[*]-(child:Person)")
          .Where("n.name='George'")
          .Return<descendant>("child.name,  length(p)") ;

I get an error that the syntax is obsolete, but I can't figure out how should I project the cypher results onto my C# POCO. Any ideas anyone?

Charlotte Skardon Charlotte Skardon · Accepted Answer · 2013-12-06T14:13:07

The query should look like this:

var query = 
    _graphClient.Cypher
        .Match("p=(n:Person)<-[*]-(child:Person)")
        .Where((Person n) => n.name == "George")
        .Return((n,p) => new descendant
        {
            name = n.As<Person>().Name,
            depth = p.Length()
        });

The Return statement should have the 2 parameters you care about (in this case n and p) and project them via the lambda syntax (=>) to create a new descendant instance. The main point this differs from the example, is that the example creates a new anonymous type, whereas you want to create a concrete type.

We then use the property initializer (code inside the { } braces) to set the name and depth, using the As<> and Length extension methods to get the values you want.

As a side note, I've also changed the Where clause to use parameters, you should always do this if you can, it will make your queries both faster and safer.

Returning composite class with Neo4jClient

1 Answers