Add support for spatial data?

[mguinness]

Many EF Core providers support spatial data with NetTopologySuite library. After adding NetTopologySuite package you add the Point type to an entity storing longitude and latitude of a location which can then be queried as follows:

var geometryFactory = NtsGeometryServices.Instance.CreateGeometryFactory(srid: 4326);
var location = geometryFactory.CreatePoint(new Coordinate(lng, lat));
var result = await ctx.Places.Where(x => x.Location.Distance(location) < 5).ToListAsync();

I did some preliminary research and it seems possible with some minor changes. Firstly you need to add GeoJSON4STJ library to the FileBaseContext project. Then you need to change the JsonRowDataSerializer class as follows:

internal static JsonSerializerOptions CreateJsonOptions(IEnumerable<JsonColumnInfo> columns)
{
    return new JsonSerializerOptions()
    {
        AllowTrailingCommas = true,
        Encoder = JavaScriptEncoder.Create(UnicodeRanges.All),
        WriteIndented = true,
        Converters =
        {
            new JsonRowDataConverter(columns),
+           new GeoJsonConverterFactory()
        },
+       NumberHandling = JsonNumberHandling.AllowNamedFloatingPointLiterals,
+       ReferenceHandler = ReferenceHandler.Preserve,
    };
}

This results in locations being serialized as follows:

"Location": {
  "type": "Point",
  "coordinates": [
    -77.036560,
    38.897957
  ]
}

There probably is more to be considered, but I thought it would be worth floating the idea to see if there is any interest.

[dualbios]

Hi, @mguinness

it would be great to have the option to add extra converters, not just that.

I created a branch named support-set-json-options, which contains an implementation of a routine that allows passing JsonSerializerOptions and merging them with the existing JSON options from DbContext into JsonRowDataSerializer.

The implementation is to extend OnConfiguring from DbContext by adding JsonSerializerOptions to a service provider

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseFileBaseContextDatabase(DatabaseName, null, services =>
        {
            services.AddMockFileSystem(_fileSystem);
            var options = new JsonSerializerOptions()
            {
                AllowTrailingCommas = true,
                Encoder = JavaScriptEncoder.Create(UnicodeRanges.All),
                WriteIndented = true,
                Converters =
                {
                    new GeoJsonConverterFactory()
                },
                NumberHandling = JsonNumberHandling.AllowNamedFloatingPointLiterals,
                ReferenceHandler = ReferenceHandler.Preserve,
            };
            services.AddSingleton(options);
        });
    }

and merge them with the built-in JsonRowDataSerializer

    internal static JsonSerializerOptions CreateJsonOptions(IEntityType entityType, JsonSerializerOptions jsonOptions) 
    {
        JsonSerializerOptions serializerOptions = CreateJsonOptions(JsonColumnInfo.FromEntityType(entityType));
        if(jsonOptions == null) {
            return serializerOptions;
        }
        
        // Merge the provided JsonSerializerOptions with the default options
        IList<JsonConverter> converters = serializerOptions.Converters.ToList();
        serializerOptions.Converters.Clear();

        foreach (JsonConverter converter in converters.Concat(jsonOptions.Converters).Distinct()) {
            serializerOptions.Converters.Add(converter);
        }
        ...
    }

I am not familiar with NetTopologySuite, so I am asking you to check my changes and create some unit tests.
You can push changes to the same branch.

[mguinness]

That's a great idea, a more flexible solution with added benefits.

The only comment I have is on configuration. Would there be a way to mimic HttpJsonServiceExtensions where you only modify the options rather than creating a new object to merge? It seems more intuitive, but maybe harder to implement?

builder.Services.ConfigureHttpJsonOptions(opt => {
    opt.SerializerOptions.Converters.Add(new GeoJsonConverterFactory());
});

EDIT: it's actually not necessary to change either NumberHandling or ReferenceHandler options when using GeoJSON4STJ.

[dualbios]

I pushed a new comment with implementation that allows for modifying the options.
Please check if it is useful.

And I kindly ask you to add some unit tests that use GeoJsonConverterFactory.

[mguinness]

Works well Kostiantyn! Made the changes you requested, but I'm unable to add to your branch. See commit mguinness@0545c7d.

Pull request creation failed. Validation failed: must be a collaborator

[dualbios]

@mguinness

A new version 5.1.0 is published.
Great job! Many thanks!

[mguinness]

Thank you! I've submitted a PR to add FileBaseContext provider to Spatial Data documentation.

Also I've created Spatial data with FileBaseContext for others looking to get started with NTS.