CODEWITHSUNDEEP
.netneo4jcypher
Rémi Chaffard
Rémi Chaffard

Reputation: 87

Neo4j .NET driver error handling

I started to use Neo4j database some days ago and I end up with an issue I don't understand with the .NET driver. I have a code like this:

using (var driver = GraphDatabase.Driver("bolt://localhost", AuthTokens.Basic("neo4j", "neo4j")))
using (var session = driver.Session())
{
    foreach(...)
        {
        // Build cypher query
        string cypher_query = "...";

        try
        {
            session.Run(cypher_query).Consume();
        }
        catch (Exception e)
        {
            Console.WriteLine("Failed running query : " + cypher_query + "\r\n" + e.Message);
        }
    }
}

I need to run a lots of cypher query (all are MERGE queries) within the foreach loop. My problem is that all queries failed after getting the first exception.

When I look what I display in the console, the cypher_query variable contains the correct thing and change at each iteration but the exception message remain always the same.

When I debug I have the feeling the query is correctly executed but we execute the catch clause anyway.

Any idea of what could happen here ?

Upvotes: 1

Views: 654

Answers (1)

Charlotte Skardon
Charlotte Skardon

Reputation: 6270

I realise this is stale, but the reason is that the exception causes the session to go into an invalid state.

This code executes to show the problem, first a wrapper method:

public static void ExecuteCypher(IDriver driver, ISession session, string cypher, bool createNewSessionOnException = true)
{
    try
    {
        //Attempt to run the cypher...
        session.Run(cypher).Consume();
    }
    catch (Exception e)
    {
        //Write out error caught
        Debug.WriteLine("Caught Exception: {0}", e.ToString());

        //If we should create a new session 
        if (createNewSessionOnException)
        {
            //first clear up the old one
            session.Dispose();

            //Create new one
            Console.WriteLine("New Session");
            session = driver.Session();
        }
    }
}

Which you call like:

using (var driver = GraphDatabase.Driver("bolt://localhost", AuthTokens.Basic("neo4j", "neo4j")))
{
    var session = driver.Session();
    ExecuteCypher(driver, session, "Broken Cypher");
    ExecuteCypher(driver, session, "Match (x) RETURN count(x)");
    session.Dispose();
}

Which will work, but if you change it so it doesn't create a new session you'll get the exception:

using (var driver = GraphDatabase.Driver("bolt://localhost", AuthTokens.Basic("neo4j", "neo4j")))
{
    var session = driver.Session();
    ExecuteCypher(driver, session, "Broken Cypher", false); //<-- here
    ExecuteCypher(driver, session, "Match (x) RETURN count(x)");
    session.Dispose();
}

Upvotes: 1

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