Writing Neo4J Cypher query in C#

Question

I have an MVC Asp.Net application that is connected to a Neo4j database. In my database there is a relationship (m:Movie)<-[r:HAS_WATCHED_MOVIE]-(u:User) between movie and user entities.

What I want to do is return a IEnumerable<Movie> that contains top 3 movies (top movies are the movies with most HAS_WATCHED_MOVIE relationsips) in descending order.

I have already figured out a Cypher query to do this, and it goes like this:

MATCH (m:Movie)<-[r:HAS_WATCHED_MOVIE]-(b) 
RETURN m, COUNT(r) 
ORDER BY COUNT(r) DESC 
LIMIT 3

Since I'm new with Neo4j C# client, I'm not sure how to go about writing this query in c#?

Answer 1

Using Neo4jClient

var client = new BoltGraphClient("bolt://localhost:7687", "neo4j", "neo");
client.Connect();

var query = client.Cypher
                  .Match("(m:Movie)<-[r:HAS_WATCHED_MOVIE]-(b)")
                  .Return((m,r) => new { 
                      Movie = m.As<Movie>(), 
                      Count = r.Count()
                   })
                  .OrderByDescending("Count")
                  .Limit(3);;

foreach(var result in query.Results)
   Console.WriteLine($"'{result.Movie.Title}' had {result.Count} watchers");

For this one, I have my Movie class defined as:

public class Movie{
    [JsonProperty("title")]
    public string Title {get;set;}
}

Using Neo4j-Driver

using (var driver = GraphDatabase.Driver("bolt://localhost:7687", AuthTokens.Basic("neo4j", "neo")))
{
    using (var session = driver.Session())
    {
        using (var tx = session.BeginTransaction())
        {
            IStatementResult results = tx.Run(
            @"MATCH (m:Movie)<-[r:HAS_WATCHED_MOVIE]-(b) 
              RETURN m, COUNT(r)
              ORDER BY COUNT(r) DESC
              LIMIT 3");
            foreach (IRecord result in results)
            {
                var node = result["m"].As<INode>();
                var title = node.Properties["title"]?.As<string>();
                var count = result["COUNT(r)"].As<long>();

                var movie = new Movie {
                      Title = title,
                };

                Console.WriteLine($"'{movie.Title}' had {count} watchers");
            }
        }
    }
}

NB. I've only done the new Movie bit in this one, as you say you wanted an IEnumerable<Movie> response.

Thoughts

The Neo4jClient one doesn't return an IEnumerable<Movie> as you're using the COUNT call in the RETURN you'd need to do something like:

var query = gc.Cypher
        .Match("(m:Movie)<-[r:HAS_WATCHED_MOVIE]-(b)")
        .With("m, COUNT(r) AS count")
        .Return((m, r) => m.As<Movie>())
        .OrderByDescending("count")
        .Limit(3);

Where you use a WITH to do the COUNT before returning. You don't have to do this with the Neo4j-Driver version as you can fake it after the fact, but I would still change the query if all you want is the Movie to:

IStatementResult results = tx.Run(
            @"MATCH (m:Movie)<-[r:HAS_WATCHED_MOVIE]-(b) 
              WITH m, COUNT(r) AS count
              RETURN m
              ORDER BY count DESC
              LIMIT 3");