fix(restheadspec): honour string URL ids on POST updates

POST with a non-numeric URL id (e.g. a string primary key) was treated as
having no id, so the body primary key was used to look up the existing row.
That broke primary key changes. Treat any non-empty, non-zero URL id as the
update target, and add an integration test through Handle for POST and PUT.

pkg/restheadspec/pk_update_integration_test.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -123,3 +124,30 @@ func TestUpdateChangesPrimaryKeyWhenURLIDGiven(t *testing.T) {
 	require.NoError(t, db.QueryRow(`SELECT category FROM public.t_pkasset WHERE description = 'new-pk'`).Scan(&cat))
 	require.Equal(t, "cat5", cat)
 }
+
+// Exercises the real dispatch: a POST with a string id in the URL and a different
+// PK in the body must update the row identified by the URL id.
+func TestHandlePostWithStringURLIDChangesPrimaryKey(t *testing.T) {
+	db := setupPKTestDB(t)
+	reg := modelregistry.NewModelRegistry()
+	require.NoError(t, reg.RegisterModel("public.t_pkasset", pkAsset{}))
+	h := NewHandler(database.NewBunAdapter(bun.NewDB(db, pgdialect.New())), reg)
+
+	for _, method := range []string{http.MethodPost, http.MethodPut} {
+		t.Run(method, func(t *testing.T) {
+			from, to := "old-pk", "new-pk-"+method
+			if method == http.MethodPut {
+				from = "new-pk-" + http.MethodPost
+			}
+			req := httptest.NewRequest(method, "/public/t_pkasset/"+from,
+				strings.NewReader(`{"description":"`+to+`","category":"c"}`))
+			rec := httptest.NewRecorder()
+			w, r := common.WrapHTTPRequest(rec, req)
+			h.Handle(w, r, map[string]string{"schema": "public", "entity": "t_pkasset", "id": from})
+
+			require.Equal(t, http.StatusOK, rec.Code, rec.Body.String())
+			require.Equal(t, 0, countPK(t, db, from))
+			require.Equal(t, 1, countPK(t, db, to))
+		})
+	}
+}