What is the best method for sending a DbGeography parameter to MVC?

Question

What is the best method for sending a DbGeography parameter to MVC?

I am working on developing an API that allows users to save polygons on the server using ASP.NET MVC 5. Can anyone guide me on how to properly format the AJAX parameters for posting requests with DbGeography? This is what I have tried so far:

$.ajax({
    url: '/api/map',
    type: 'POST',
    data: {
        Title: 'My Title',
        MyGEOG: {
            WellKnownText: 'POLYGON ((30 10, 10 20, 20 40, 40 40, 30 10))'
        }
    }
});

Here is my MVC action method signature:

    [HttpPost]
    [Route("map")]
    public JsonResult Post(MyShape newShape) {...}

In addition, here's my MyShape class:

public class MapShape
{
    public string Title { get; set; }
    public System.Data.Entity.Spatial.DbGeography MyGEOG { get; set; }
}

When debugging the action, I notice that newShape.Title correctly displays as My Title, but MyGEOG is null during the AJAX post request. Can someone advise on the correct parameter format to successfully post as a DbGeography type?

javascript ajax asp.net-mvc entity-framework geospatial

Answer 1

Answer №1

The DBGeography object is designed to be immutable, meaning that once it is created, you cannot modify its properties. This becomes an issue when trying to instantiate the MapShape class in the model binder and finding the MyGEO property to be null, essentially attempting to set a property on a null object.

If you need to create a DBGeography object, you must utilize one of the factory methods such as:

FromText - Generates a new DbGeometry value using the specified well-known text representation. http://msdn.microsoft.com/en-us/library/hh673669(v=vs.110).aspx

To pass both the Title and WellKnownText values to your controller, I recommend creating a Data Transfer Object (DTO) to serve as a middleman for the data.

public class MapShapeDTO
{
    public string Title { get; set; } 
    public string WellKnownText { get; set; }
}

Your AJAX call can be simplified like so:

$.ajax({
url: '/api/map',
type: 'POST',
data: {
    Title: 'My Title',
    WellKnownText: 'POLYGON ((30 10, 10 20, 20 40, 40 40, 30 10))'
    }
});

In your controller, you can then use the DTO to construct the MapShape object.

[HttpPost]
[Route("map")]
public JsonResult Post(MapShapeDTO dto)
    {
        MapShape m = new MapShape()
            {
                Title = dto.Title,
                MyGEOG = System.Data.Entity.Spatial.DbGeography.FromText(dto.WellKnownText)
            };
      ...
    }

Answer 2

The DBGeography object is designed to be immutable, meaning that once it is created, you cannot modify its properties. This becomes an issue when trying to instantiate the MapShape class in the model binder and finding the MyGEO property to be null, essentially attempting to set a property on a null object.

If you need to create a DBGeography object, you must utilize one of the factory methods such as:

FromText - Generates a new DbGeometry value using the specified well-known text representation. http://msdn.microsoft.com/en-us/library/hh673669(v=vs.110).aspx

To pass both the Title and WellKnownText values to your controller, I recommend creating a Data Transfer Object (DTO) to serve as a middleman for the data.

public class MapShapeDTO
{
    public string Title { get; set; } 
    public string WellKnownText { get; set; }
}

Your AJAX call can be simplified like so:

$.ajax({
url: '/api/map',
type: 'POST',
data: {
    Title: 'My Title',
    WellKnownText: 'POLYGON ((30 10, 10 20, 20 40, 40 40, 30 10))'
    }
});

In your controller, you can then use the DTO to construct the MapShape object.

[HttpPost]
[Route("map")]
public JsonResult Post(MapShapeDTO dto)
    {
        MapShape m = new MapShape()
            {
                Title = dto.Title,
                MyGEOG = System.Data.Entity.Spatial.DbGeography.FromText(dto.WellKnownText)
            };
      ...
    }

What is the best method for sending a DbGeography parameter to MVC?

Answer №1

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