Polygon conversion

A polygon represents an exterior boundary and optional holes. Arc’s AsPolygon() converts the record to a plain JSON string. It is not automatically applied by BaseDbContext and is not native spatial mapping.

Define and configure an area

Model declaration:

using Cratis.Geospatial;

public class ServiceArea
{
    public int Id { get; set; }
    public required Polygon Boundary { get; set; }
}

Inside OnModelCreating, with Cratis.Arc.EntityFrameworkCore and Microsoft.EntityFrameworkCore imported:

modelBuilder.Entity<ServiceArea>().Property(area => area.Boundary).AsPolygon();

Construction fragment inside a method:

var boundary = new Polygon(
    new LinearRing([
        new Point(0, 0),
        new Point(1, 0),
        new Point(0, 1),
        new Point(0, 0)
    ]),
    Holes: []);

Plain JSON conversion writes Shell and Holes; rings contain Coordinates arrays of objects with Longitude and Latitude. It does not write GeoJSON’s type and nested numeric coordinate arrays.

Validate boundaries yourself

Neither the Fundamentals records nor AsPolygon() enforce ring closure, minimum point count, winding, or freedom from self-intersection. Your application must validate the geometry it requires. Use closed rings with at least three distinct vertices and a repeated closing point when targeting GeoJSON-compatible storage.

The converter does not add a structural value comparer. Replace values deliberately and test change tracking when arrays or rings are modified. Do not promise SQL translation for containment or intersection from string conversion alone.

Migrations

There is no PolygonColumn() helper for CreateTable. The distinct AddPolygonColumn() helper selects geometry(Polygon, 4326) on PostgreSQL, geography on SQL Server, and TEXT on SQLite. Those declarations do not install a compatible value converter or database spatial extension.

Choose a representation using the storage-path matrix. See JSON conversion for [Json] properties and adding columns for migration helpers.