IsWithinDistance could not be translated

Question

I'm trying to return a list of items that are within say 50 Miles of a given location.

My table (simplified) is as follows:

• Id
• Longitude
• Latitude
• Status
• Active

I've got an initial query:

var query = db.MyTable.Where(o=> o.Status == "New" && o.Active == true);

query = query.Where(o => new Point(o.Longitude, o.Latitude)
                  .IsWithinDistance(new Point(_currentLongitude, _currentLatitude), 50));

var result = query.ToList()

However - it doesn't seem to work and am getting an error as below - any ideas how to solve this? or if there is a better way to get the nearest items?

.Where(p => new Point(p.Longitude, p.Latitude) .IsWithinDistance(geom: __p_3,
distance: ___maxDistance_4))' could not be translated.

Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

Startup.cs:

services.AddDbContext<AppDbContext>(options =>
{
                
 options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"),
   x => x.UseNetTopologySuite());
});

Answer 1

To make this feature work, you will need to have those coordinates stored as a Point in a SQL geography field. You can easily add this to your existing model as a computed column on a new property.

// on your entity
public Point Coordinates { get; }

// in your db context's OnModelCreating
  modelBuilder.Entity<YourEntity>()
    .Property(x => x.Coordinates)
    .IsRequired()
    .HasComputedColumnSql("geography::Point(Latitude, Longitude, 4326)");

Note, SRID 4326 is the commonly used lat/lon coordinate system supported by SQL Server. More on that here.

Build your model and deploy to your database.

Now that you have a spatial field and property, you can query like this:

var point = new Point(_currentLongitude, _currentLatitude) { SRID = 4326 };
var distanceInMeters = 50 * 1609.344;  // 50 miles to meters conversion
var results = db.YourEntity
                .Where(x => x.Coordinates.IsWithinDistance(point, distanceInMeters))
                .ToList();

SRID 4326 uses meters for distance, so be sure to convert as shown above if you are using miles.

Also, if you have a lot of data you will also want to add a spatial index on that column, but EF Core doesn't support that directly yet so you'll have to do that directly in SQL.