Do not create migrations when changing field types

Fixes #30, 32.

form_designer/migrations/0001_initial.py

@@ -2,24 +2,6 @@
 from django.db import models, migrations
 
 
-field_types = [
-    ("text", "text"),
-    ("email", "email address"),
-    ("longtext", "long text"),
-    ("checkbox", "checkbox"),
-    ("select", "select"),
-    ("radio", "radio"),
-    ("multiple-select", "multiple select"),
-    ("hidden", "hidden"),
-]
-try:
-    from form_designer.models import FIELD_TYPES
-
-    field_types = [type[:2] for type in FIELD_TYPES]
-except Exception:
-    pass
-
-
 class Migration(migrations.Migration):
 
     dependencies = []
@@ -61,7 +43,7 @@ class Migration(migrations.Migration):
                 (
                     "type",
                     models.CharField(
-                        verbose_name="field type", choices=field_types, max_length=20
+                        verbose_name="field type", choices=[("", "")], max_length=20
                     ),
                 ),
                 (

form_designer/models.py

@@ -174,6 +174,15 @@ def process(self, form, request):
     }
 
 
+class _StaticChoicesCharField(models.CharField):
+    """Does not detect changes to "choices", ever"""
+
+    def deconstruct(self):
+        name, path, args, kwargs = super(_StaticChoicesCharField, self).deconstruct()
+        kwargs["choices"] = [("", "")]
+        return name, "django.db.models.CharField", args, kwargs
+
+
 class FormField(models.Model):
     form = models.ForeignKey(
         Form, related_name="fields", verbose_name=_("form"), on_delete=models.CASCADE
@@ -182,7 +191,7 @@ class FormField(models.Model):
 
     title = models.CharField(_("field title"), max_length=100)
     name = models.CharField(_("field name"), max_length=100)
-    type = models.CharField(
+    type = _StaticChoicesCharField(
         _("field type"),
         max_length=20,
         choices=[(type["type"], type["verbose_name"]) for type in FIELD_TYPES],