connecting

Getting Connected

You first need to include a reference to the Neo4jClient nuget package. This will add all the required dependencies to the project.

Graph Client Basics

There are two classes which connect to Neo4j, the choice between them comes down to how you want to connect to your server (or indeed how you can).

• GraphClient - provides an HTTP based connection
• BoltGraphClient - provides a Bolt based connection

This is the entry point for all further operations. For testability they both implement the IGraphClient interface. This also means you can swap between the two clients without changing the rest of your codebase.

You need to instantiate, then connect the client prior to use:

//HTTP
var graphClient = new GraphClient("http://localhost:7474/db/data", "username", "password");
await graphClient.ConnectAsync();

//Bolt
var boltGraphClient = new BoltGraphClient("neo4j://localhost:7687", "username", "password");
await boltGraphClient.ConnectAsync();

The ConnectAsync method sends a request to the root of the REST/Bolt API to discover where the required API endpoints are. As such, the ConnectAsync method needs to be called before anything else is called on the client.

(Development note: ConnectAsync was implemented as a separate method because constructors shouldn't throw exceptions.)

Threading and Lifecycles

GraphClient and BoltGraphClient are thread safe. You should only have one instance of either for each database that you want to talk to (typically, one). This avoids excess calls to the ConnectAsync() method which requires a roundtrip to the Neo4j server.

As an example, if you were using Autofac, you could register the graph client like so:

    containerBuilder
        .Register<IGraphClient>(context =>
        {
            var graphClient = new GraphClient("http://localhost:7474/db/data", "username", "password");
            var connectTask = graphClient.ConnectAsync();
            connectTask.Wait();
            return graphClient;
        })
        .SingleInstance();

The BoltGraphClient should be used in the same way:

    containerBuilder
        .Register<IGraphClient>(context =>
        {
            var graphClient = new BoltGraphClient("neo4j://localhost:7687", "username", "password");
            var connectTask = graphClient.ConnectAsync();
            connectTask.Wait();
            return graphClient;
        })
        .SingleInstance();

---

HTTP Client (GraphClient) Specific

This only applies to the GraphClient class.

You can use a single NeoServerConfiguration object to create a GraphClient per request instead of using a Singleton. This may be beneficial for hi-transaction environments where a ConcurrentTransactionException may occur on the server when using a single GraphClient instance.

NeoServerConfiguration Example

Composition root (autofac example):

    public void Register()
    {
        containerBuilder
            .Register<NeoServerConfiguration>(context => NeoServerConfiguration.GetConfiguration(uri, user, pwd))
            .SingleInstance();

        containerBuilder
            .RegisterType<GraphClientFactory>()
            .As<IGraphClientFactory>()
            .SingleInstance();
    }

Service level:

    public class NeoServiceClass
    {
        private readonly IGraphClientFactory factory;
        ...
        public async Task ExecuteQueryAsync()
        {
            using (var client = factory.Create())
            {
                // query body
                await client.Cypher.Query.ExecuteWithoutResultsAsync();
            }
        }
    }