Neo4jClient - query relationship

Question

Trying to look at a relationship in a query like this:

var query = _graph.Cypher.Start(
new
{
    me = Node.ByIndexLookup("node_auto_index", "id", p.id)
}).Match("me-[r:FRIENDS_WITH]-friend")
.Where((Person friend) => friend.id == f.id)
.Return<FriendsWith>("r");

Here is the FriendsWith class. I can't add a parameterless constructor for FriendsWith, because the base class (Relationship) doesn't have a parameterless constructor.

public class FriendsWith : Relationship,
        IRelationshipAllowingSourceNode<Person>,
        IRelationshipAllowingTargetNode<Person>
    {
        public FriendsWith(NodeReference<Person> targetNode)
            : base(targetNode)
        {
            __created = DateTime.Now.ToString("o");
        }
        public const string TypeKey = "FRIENDS_WITH";
        public string __created { get; set; }
        public override string RelationshipTypeKey
        {
            get { return TypeKey; }
        }

    }

But I get the error "No parameterless constructor defined for this object." when I try to run it. What is the proper way to return a relationship for a query?

Stack trace

at Neo4jClient.Deserializer.CypherJsonDeserializer1.Deserialize(String content) in c:\TeamCity\buildAgent\work\f1c4cf3efbf1b05e\Neo4jClient\Deserializer\CypherJsonDeserializer.cs:line 53 at Neo4jClient.GraphClient.<>c__DisplayClass1d1.b__1c(Task1 responseTask) in c:\TeamCity\buildAgent\work\f1c4cf3efbf1b05e\Neo4jClient\GraphClient.cs:line 793 at System.Threading.Tasks.ContinuationResultTaskFromResultTask2.InnerInvoke() at System.Threading.Tasks.Task.Execute()

Maybe you're missing the default (parameterless) constructor for the class FriendsWith? — veljkoz
You can add a default constructor, you just pass a dummy value to the base constructor something like: public FriendsWith():base(-1){} — Charlotte Skardon

Tatham Oddie Tatham Oddie · Accepted Answer · 2013-10-25T23:04:32

Just deserialize it into a POCO that represents the data structure:

public class FriendsWith
{
    public string __created { get; set; }
}

var query = _graph.Cypher
    .Start(new {
        me = Node.ByIndexLookup("node_auto_index", "id", p.id)
    })
    .Match("me-[r:FRIENDS_WITH]-friend")
    .Where((Person friend) => friend.id == f.id)
    .Return(r => r.As<FriendsWith>())
    .Results;

You actually don't need the FriendsWith : Relationship, IRelationshipAllowingSourceNode<Person>, IRelationshipAllowingTargetNode<Person> class at all.

Create relationships using Cypher:

_graph.Cypher
    .Start(new {
        me = Node.ByIndexLookup("node_auto_index", "id", p.id),
        friend = Node.ByIndexLookup("node_auto_index", "id", p.id + 1)
    })
    .CreateUnique("me-[:FRIENDS_WITH {data}]->friend")
    .WithParams(new { data = new FriendsWith { __created = DateTime.Now.ToString("o") } })
    .ExecuteWithoutResults();

You'll see more examples on the Neo4jClient wiki. Basically, in this day and age, everything should be Cypher.

Neo4jClient - query relationship

1 Answers