From 6bb595384bbe8e2f960c3a1df0e4e66c9da3e884 Mon Sep 17 00:00:00 2001
From: Paul Mach <paulmach@gmail.com>
Date: Fri, 20 Mar 2015 14:14:53 -0700
Subject: [PATCH] geometry.Scan for direct postgis query -> geojson

---
 README.md        | 15 +++++++++++----
 geometry.go      | 13 +++++++++++++
 geometry_test.go | 22 ++++++++++++++++++++++
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 236b7b2..9ecaf1b 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,10 @@
 go.geojson
 ==========
 
-go.geojson is a library for **encoding and decoding** [GeoJSON](http://geojson.org/) into Go structs.
+Go.geojson is a package for **encoding and decoding** [GeoJSON](http://geojson.org/) into Go structs.
 Supports both the [json.Marshaler](http://golang.org/pkg/encoding/json/#Marshaler) and [json.Unmarshaler](http://golang.org/pkg/encoding/json/#Unmarshaler)
-interfaces as well as helper functions such as `UnmarshalFeatureCollection`, `UnmarshalFeature` and `UnmarshalGeometry`.
+interfaces as well as [sql.Scanner](http://golang.org/pkg/database/sql/#Scanner) for directly scanner PostGIS query results.
+The package also provides helper functions such as `UnmarshalFeatureCollection`, `UnmarshalFeature` and `UnmarshalGeometry`.
 
 #### To install
 	
@@ -48,8 +49,7 @@ interfaces as well as helper functions such as `UnmarshalFeatureCollection`, `Un
 
 		g.IsPoint() == true
 		g.Point == []float64{102.0, 0.5}
-
-
+	
 * #### Marshalling (Go -> JSON)
 
 		g := geojson.NewPointGeometry([]float64{1, 2})
@@ -59,6 +59,13 @@ interfaces as well as helper functions such as `UnmarshalFeatureCollection`, `Un
 		fc.AddFeature(geojson.NewPointFeature([]float64{1,2}))
 		rawJSON, err := fc.MarshalJSON()
 
+* #### Scanning PostGIS query results
+
+		row := db.QueryRow("SELECT ST_AsGeoJSON(the_geom) FROM postgis_table)
+
+		var geometry *geojson.Geometry
+		row.Scan(&geometry)
+
 * #### Dealing with different Geometry types
 
 	A geometry can be of several types, causing problems in a statically typed language.
diff --git a/geometry.go b/geometry.go
index 70d66c8..76d9d6f 100644
--- a/geometry.go
+++ b/geometry.go
@@ -154,6 +154,19 @@ func (g *Geometry) UnmarshalJSON(data []byte) error {
 	return decodeGeometry(g, object)
 }
 
+// Scan implements the sql.Scanner interface allowing
+// geometry structs to be passed into rows.Scan(...interface{})
+// The columns must be received as GeoJSON Geometry.
+// When using PostGIS a spatial column would need to be wrapped in ST_AsGeoJSON.
+func (g *Geometry) Scan(value interface{}) error {
+	data, ok := value.([]byte)
+	if !ok {
+		return errors.New("unable to parse this type into geojson")
+	}
+
+	return g.UnmarshalJSON(data)
+}
+
 func decodeGeometry(g *Geometry, object map[string]interface{}) error {
 	t, ok := object["type"]
 	if !ok {
diff --git a/geometry_test.go b/geometry_test.go
index fa728a5..871da23 100644
--- a/geometry_test.go
+++ b/geometry_test.go
@@ -262,3 +262,25 @@ func TestUnmarshalGeometryCollection(t *testing.T) {
 		t.Errorf("should have 2 geometries but got %d", len(g.Geometries))
 	}
 }
+
+func TestGeometryScan(t *testing.T) {
+	g := &Geometry{}
+
+	err := g.Scan(123)
+	if err == nil {
+		t.Errorf("should return error if not the correct data type")
+	}
+
+	err = g.Scan([]byte(`{"type":"Point","coordinates":[-93.787988,32.392335]}`))
+	if err != nil {
+		t.Fatalf("should parse without error, got %v", err)
+	}
+
+	if !g.IsPoint() {
+		t.Errorf("should be point, but got %v", g)
+	}
+
+	if g.Point[0] != -93.787988 || g.Point[1] != 32.392335 {
+		t.Errorf("incorrect point data, got %v", g.Point)
+	}
+}