Entity Framework Core Polygon conversion

Use Arc’s AsPolygon() to store an area’s exterior boundary and optional holes as a plain JSON string in Entity Framework Core. Configure the property explicitly: BaseDbContext does not apply this converter automatically. The string conversion does not provide native spatial mapping.

Define and configure an area

Define an area with a Cratis.Geospatial.Polygon property:

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();

Inside a method, construct the boundary from a closed exterior ring. This example has no holes:

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

The stored JSON has Shell and Holes properties. Each ring contains a Coordinates array of objects with Longitude and Latitude. This differs from GeoJSON, the geographic JSON format that uses a type property and nested numeric coordinate arrays.

Validate boundaries yourself

Neither the Cratis.Geospatial records nor AsPolygon() validates that a ring closes, has enough points, runs in the required direction, or avoids crossing itself. Validate the geometry your application requires before saving it. For GeoJSON-compatible rings, use at least three distinct vertices and repeat the first point at the end; this does not turn the converter’s output into GeoJSON.

The converter does not add a structural value comparer to compare the contents of arrays and rings. Replace values deliberately and verify EF change tracking when those contents change. String conversion alone does not translate containment or intersection queries into SQL.

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.