How to seed NetTopologySuite.Geometries.Point data from a Json file in ASP.Net core

问题

I want to seed "Location" data for my user object from my seed file

The c# object, where Point is a NetTopologySuite.Geometries.Point is part of my user object

  public class User: IdentityUser<int> {
      // member data here
      public Point Location { get; set; } // has lat/lng data points
  }

I seed data to my db on startup by doing something like this

public void SeedUsers()
{
    if (!_userManager.Users.Any())
    {
        var userData = System.IO.File.ReadAllText("Data/UserSeedData.json");
        var users = JsonConvert.DeserializeObject<List<User>>(userData);

        var roles = new List<Role>
        {
            new Role{Name = "Member"},
            new Role{Name = "Admin"},
            new Role{Name = "Moderator"},
            new Role{Name = "VIP"},
        };

        foreach (var role in roles)
        {
            _roleManager.CreateAsync(role).Wait();
        }

        foreach (var user in users)
        {
            user.Photos.SingleOrDefault().IsApproved = true;
            _userManager.CreateAsync(user, "password").Wait();
            _userManager.AddToRoleAsync(user, "Member").Wait();
        }
     }
 }

with a json file "UserSeedData.json" of json arrays like this and I want to be able to stick some kind of 'Location' data in there that is representative of lng/lat data points.

{
  "Email": "myemailaddress@gmail.com",
  "Username": "Lola",
  "Gender": "female",
  "DateOfBirth": "1994-02-21",
  "Password": "password",
  "Created": "2017-08-02",
  "LastActive": "2017-08-02",
  "Introduction": "blah blah blah",
  "LookingFor": "blah blah blah",
  "City": "San Francisco",
  "Country": "United States",
  "Longitude": -122.431297,
  "Latitude": 37.773972,
  "Location": // something here!!!
  "Photos": [{
    "url": "https://randomuser.me/api/portraits/women/3.jpg",
    "isMain": true,
    "description": "Non deserunt labore sunt ex laboris et adipisicing ullamco officia minim."
  }]
}

Now I know in my seed method I could do something like this, but I'm looking for a way to include it in my .json file, so I can use different data points

foreach (var user in users)
{
    user.Photos.SingleOrDefault().IsApproved = true;
    user.Location = new Point(-122.4194155, 37.7749295) { SRID = 4326 };
    _userManager.CreateAsync(user, "password").Wait();
    _userManager.AddToRoleAsync(user, "Member").Wait();
}

回答1:

You could subclass NetTopologySuite.Geometries.Point and add a [JsonConstructor] to parse your json file. It should be a straightforward substitution for the rest of your code.

public class MyPoint : Point
{
    [JsonConstructor]
    public MyPoint(double latitude, double longitude, int srid)
        :base(new GeoAPI.Geometries.Coordinate(longitude, latitude))
    {
        SRID = srid;
    }
}

Note that latitude = y and longitude = x so the order is reversed.

Swap MyPoint for Point in your User class

public class User: IdentityUser<int> {
  // member data here
  public MyPoint Location { get; set; }
}

And it should work with your json as is.

回答2:

NetTopologySuite has a separate nuget, NetTopologySuite.IO.GeoJSON, for serializing NetTopologySuite types from and to JSON using Json.NET. It includes converters for geometry objects such as Point. If you add this nuget to your project you will be able to add geometry entities such as Point to your data model and (de)serialize the model directly.

To do this, first add NetTopologySuite.IO.GeoJSON to your project.

Then add the following extension method:

public static partial class JsonExtensions
{
    public static T LoadFromFileWithGeoJson<T>(string path, JsonSerializerSettings settings = null)
    {
        var serializer = NetTopologySuite.IO.GeoJsonSerializer.CreateDefault(settings);
        serializer.CheckAdditionalContent = true;
        using (var textReader = new StreamReader(path))
        using (var jsonReader = new JsonTextReader(textReader))
        {
            return serializer.Deserialize<T>(jsonReader);
        }
    }
}

And add a Location property to your User model as in your question:

public class User : IdentityUser<int>
{
    public Point Location { get; set; }

    // Remainder unchanged.
    // ...
}

Now, the JSON format for a Point looks like:

{"type":"Point","coordinates":[-122.431297,37.773972]}

So edit your JSON file to look like:

[
  {
    "Location": {
      "type": "Point",
      "coordinates": [
        -122.431297,
        37.773972
      ]
    },
    // Remainder unchanged

Having done all this, you will be able to deserialize your JSON file quite simply as follows:

var users = JsonExtensions.LoadFromFileWithGeoJson<List<User>>("Data/UserSeedData.json");

Notes:

NetTopologySuite.IO.GeoJSON requires Newtonsoft.Json version 9.0.1 or greater. If you are using a later version you may need to add a bindingRedirect to avoid build warnings.
See HowTo use [NetTopologySuite.IO.GeoJSON] with ASP.NET Core for additional information on integrating this package in your project.
The SRID seems not to be saved as part of the point's JSON. Instead it is set by the IGeometryFactory used when deserializing the Point, which by default is new GeometryFactory(new PrecisionModel(), 4326);.

If you need control over this you can construct a JsonSerializer using a specific factory by using GeoJsonSerializer.Create(IGeometryFactory factory).

Demo fiddle here.

回答3:

Because the NetTopologiySuite's Point object doesn't contain a parameterless constructor you can't easily map the JSON during deserailization.

But, you can easily create your own Location object and then map the values to the NetTopologySuite's Point object within your loop.

First, define a new Location object...

public class Location
{
    public double Longitude { get; set; }
    public double Latitude { get; set; }
    public int SRID { get; set; }
}

Next, update your JSON's location line with the below line to define the Location object:

"Location": {"Longitude":-122.4194155, "Latitude":37.7749295, "SRID":4326},

Full JSON:

[{
        "Email": "myemailaddress@gmail.com",
        "Username": "Lola",
        "Gender": "female",
        "DateOfBirth": "1994-02-21",
        "Password": "password",
        "Created": "2017-08-02",
        "LastActive": "2017-08-02",
        "Introduction": "blah blah blah",
        "LookingFor": "blah blah blah",
        "City": "San Francisco",
        "Country": "United States",
        "Longitude": -122.431297,
        "Latitude": 37.773972,
        "Location": {"Longitude":-122.4194155, "Latitude":37.7749295, "SRID":4326},
        "Photos": [{
            "url": "https://randomuser.me/api/portraits/women/3.jpg",
            "isMain": true,
            "description": "Non deserunt labore sunt ex laboris et adipisicing ullamco officia minim."
        }]
    }]

Next, update your User object to use your new Location object and set the JsonIgnore attribute on the NetTopologySuite's Point object:

public class User : IdentityUser<int>
{
    // member data here

    public Location Location { get; set; }

    [JsonIgnore]
    public Point LocationPoint { get; set; } // has lat/lng data points
}

Finally, update your foreach loop to map the data...

foreach (var user in users)
{
    user.Photos.SingleOrDefault().IsApproved = true;
    user.LocationPoint = new Point(user.Location.Longitude, user.Location.Latitude) {SRID = user.Location.SRID};
    _userManager.CreateAsync(user, "password").Wait();
    _userManager.AddToRoleAsync(user, "Member").Wait();
}

All said and done, you may want to reconsider using the NetTopologySuite's Point object directly within your User object, and instead use your own Location object. Then you would transpose to the NetTopologySuite's Point object closer to the code that actually uses the Point. This really depends on your application though.

来源：https://stackoverflow.com/questions/57172968/how-to-seed-nettopologysuite-geometries-point-data-from-a-json-file-in-asp-net-c

标签

json

asp.net-core-2.2

nettopologysuite