ch8.2

cmd/api/errors.go

@@ -43,3 +43,8 @@ func (app *application) badRequestResponse(w http.ResponseWriter, r *http.Reques
 func (app *application) failedValidationResponse(w http.ResponseWriter, r *http.Request, errors map[string]string) {
 	app.errorResponse(w, r, http.StatusUnprocessableEntity, errors)
 }
+
+func (app *application) editConflictResponse(w http.ResponseWriter, r *http.Request) {
+	message := "unable to update the record due to an edit conflict, please try again"
+	app.errorResponse(w, r, http.StatusConflict, message)
+}

cmd/api/movies.go

@@ -127,7 +127,12 @@ func (app *application) updateMovieHandler(w http.ResponseWriter, r *http.Reques
 
 	err = app.models.Movies.Update(movie)
 	if err != nil {
-		app.serverErrorResponse(w, r, err)
+		switch {
+		case errors.Is(err, data.ErrEditConflict):
+			app.editConflictResponse(w, r)
+		default:
+			app.serverErrorResponse(w, r, err)
+		}
 		return
 	}
 

internal/data/models.go

@@ -7,6 +7,7 @@ import (
 
 var (
 	ErrRecordNotFound = errors.New("record not found")
+	ErrEditConflict   = errors.New("edit conflict")
 )
 
 type Models struct {

internal/data/movies.go

@@ -70,7 +70,7 @@ func (m MovieModel) Update(movie *Movie) error {
 	query := `
 		UPDATE movies
 		SET title=$1, year=$2, runtime=$3, genres=$4, version = version + 1
-		WHERE id = $5
+		WHERE id = $5 AND version = $6
 		RETURNING version`
 
 	args := []any{
@@ -79,9 +79,20 @@ func (m MovieModel) Update(movie *Movie) error {
 		movie.Runtime,
 		pq.Array(movie.Genres),
 		movie.ID,
+		movie.Version,
 	}
 
-	return m.DB.QueryRow(query, args...).Scan(&movie.Version)
+	err := m.DB.QueryRow(query, args...).Scan(&movie.Version)
+	if err != nil {
+		switch {
+		case errors.Is(err, sql.ErrNoRows):
+			return ErrEditConflict
+		default:
+			return err
+		}
+	}
+
+	return nil
 }
 
 func (m MovieModel) Delete(id int64) error {