Feedback for the object mapping feature in the .NET driver

[RichardIrons-neo4j]

Object mapping has been added the the .NET driver as a preview feature by way of these two PRs:

Initial PR to add object mapping
Second PR to add constructor mapping

If you're a .NET developer, it would be really helpful if you could give this feature a try, and let us know your thoughts - whether you found a bug, have an idea for a feature that should be added, or anything else you'd like to share, please do so here. Thank you!

[williambohrmann3]

This is such a great feature! I was wondering if/how mapping relationships to C# objects was intended with this functionality. Object mapping has been working perfectly for nodes! Creating an object class for the relationship with the attributes is easy enough. What I don't find straight forward is determining the start and end nodes as (which are also mapped objects) of the relationship in C#. My thought was to create start and end nodes as fields.

For example, (Interaction)-[:OCCURED { bool indoors }]->(Location). The Interaction and Location, nodes have been successfully mapped. The OCCURED relationship has also been mapped but really just contains the wasIndoors bool since I can't figure out a great way to reference the previously created Interaction and Location nodes.

public abstract class Related(object startNode, object endNode)
{
    public object StartNode => startNode;
    public object EndNode => endNode;
}
public class Occurred(Interaction interaction, Location location, bool indoors) : Related(interaction, location)
{
    public bool Outdoors => outdoors;
    public bool Indoors => indoors;
}

Happy to learn if there's a better way of determining start/end nodes of the relationship in C# than what I've tried.

[RichardIrons-neo4j]

Hi - thanks so much for taking the time to post this.

This is a feature that we definitely want to put in, but it's a "phase 2" feature, along with the ability to map query results to anonymous types. For now I'm afraid you'll have to manage those links yourself. Please do let us know what you think of everything you've used so far and if there are any other features you'd like to see - feedback is really helpful.

It's worth noting as well that when the next version of the driver is released, the default mapper will become case sensitive, and it will stop searching through nodes and dictionaries for properties (since both of these could produce unpredictable results in certain situations). If you're using any of these you'll need to put [MappingSource] attributes on the properties or constructor parameters concerned.

Again, many thanks for your post!

[williambohrmann3]

Thank you for the heads up @RichardIrons-neo4j! I am new to the Neo4j.NET driver and had some overall feedback with the driver. A great feature would be a query result visualization tool. When querying on Neo4j Desktop, we get to visually see our results as a subset of the graph. It would be awesome to be able to do this in a .NET app, perhaps it could be a UI control like microsoft/automatic-graph-layout, or some sort of webview window. My use case for this would be visualizing the relationships for a no-code application. Also, a roadmap would be awesome to have so I'm able to better anticipate changes to the driver. And a more comprehensive doc reference and more atomic code samples would be huge. Overall, I am finding the driver to be a really powerful way to manage data in my app prototype and am looking forward to future developments! Sorry if any of this already exists and deviating from object mapping specifically in my reply.

[enriko-riba]

Can you also add auto mapping Labels and ElementId if such members exist on the dto? e.g.
public record GenericNode(string ElementId, string[]? Labels, IReadOnlyDictionary<string, object>? Properties);
or
public record IotDevice(string UUID, string Model, string[]? Labels);

[RichardIrons-neo4j]

Hi there. We don't currently have support for getting an ElementId (although you could return it as a field in your query and map that maybe?), but if one of the fields in the record is a Node, then you can get the labels of that node with a [MappingSource] attribute, like so:

public record Sample (
    // ...
    [MappingSource("nodeName", EntityMappingSource.NodeLabel)] List<string> labels,
    // ...
    );

Or instead of a List<string> you could use a plain string and you will get a comma-separated list.

I do see something missing here: if you are mapping one of the fields in the record directly to an object, there needs to be a way to get the labels into that object. I will have a think on how that could be achieved.

It's not the first time people have asked to get the ElementId, so we will definitely be looking at getting that in there too.

[enriko-riba]

I do not really care much about the ElementId itself, I am just trying to connect nodes and relationships - the same issue as the previous poster had.
If the relationship field contains:

        "type": "INSIDE",
        "properties": {},
        "elementId": "5:2332746a-bdc5-48f2-942b-489db1930803:1152921504606847198",
        "startNodeElementId": "4:2332746a-bdc5-48f2-942b-489db1930803:222",
        "endNodeElementId": "4:2332746a-bdc5-48f2-942b-489db1930803:11"

I am searching for a way to find nodes the start/end element IDs are pointing to. If this is the wrong way of doing it any suggestion is welcome.

Regarding labels, I am using a custom IRecordMapper in the line of:

public GenericNode Map(IRecord record)
{
    var key = record.Keys[0];
    var node = record[key].As<INode>();
    return new GenericNode(node.ElementId, [.. node.Labels], node.Properties);
}

But would love if the default mapper could do it out of the box. When using MappingSource attributes It is hard to marry the parameterless ctor requirement with c# records, but again just starting to learn about the .Net driver so I am probably completely of course here as well.