fix(user): allow deleting a user if they have a default project

Resolves https://github.com/go-vikunja/api/issues/78

pkg/models/project.go

@@ -960,7 +960,8 @@ func (p *Project) Delete(s *xorm.Session, a web.Auth) (err error) {
 	if err != nil {
 		return err
 	}
-	if isDefaultProject {
+	// Owners should be allowed to delete the default project
+	if isDefaultProject && p.OwnerID != a.GetID() {
 		return &ErrCannotDeleteDefaultProject{ProjectID: p.ID}
 	}
 
@@ -988,6 +989,16 @@ func (p *Project) Delete(s *xorm.Session, a web.Auth) (err error) {
 		return
 	}
 
+	// If we're deleting a default project, remove it as default
+	if isDefaultProject {
+		_, err = s.Where("default_project_id = ?", p.ID).
+			Cols("default_project_id").
+			Update(&user.User{DefaultProjectID: 0})
+		if err != nil {
+			return
+		}
+	}
+
 	// Delete the project
 	_, err = s.ID(p.ID).Delete(&Project{})
 	if err != nil {

pkg/models/user_delete_test.go

@@ -58,4 +58,17 @@ func TestDeleteUser(t *testing.T) {
 		assert.NoError(t, err)
 		// No assertions for deleted projects since that user doesn't have any
 	})
+	t.Run("user with a default project", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+		notifications.Fake()
+
+		u := &user.User{ID: 16}
+		err := DeleteUser(s, u)
+
+		assert.NoError(t, err)
+		db.AssertMissing(t, "users", map[string]interface{}{"id": u.ID})
+		db.AssertMissing(t, "projects", map[string]interface{}{"id": 37}) // only user16 had access to this project, and it was their default
+	})
 }