Adds the ability to move in a form class

HISTORY.rst

@@ -1,5 +1,9 @@
 Changelog
 ---------
+
+- Adds the ability to move in a form class.
+  [href]
+
 0.13.0 (2016-08-30)
 ~~~~~~~~~~~~~~~~~~~
 

onegov/form/__init__.py

@@ -10,7 +10,13 @@
     FormSubmissionCollection,
     FormDefinitionCollection
 )
-from onegov.form.core import FieldDependency, Form, merge_forms, with_options
+from onegov.form.core import (
+    FieldDependency,
+    Form,
+    merge_forms,
+    move_fields,
+    with_options,
+)
 from onegov.form.display import render_field
 from onegov.form.models import (
     FormDefinition,
@@ -32,8 +38,9 @@
     'FormSubmissionCollection',
     'FormSubmissionFile',
     'merge_forms',
+    'move_fields',
     'parse_form',
     'PendingFormSubmission',
     'render_field',
-    'with_options'
+    'with_options',
 ]

onegov/form/core.py

@@ -447,17 +447,62 @@ class Merged(*forms):
     class MergedForm(*forms):
         pass
 
-    processed = set()
     fields_in_order = (
         name for cls in forms for name, field
         in utils.get_fields_from_class(cls)
     )
 
+    return enforce_order(MergedForm, fields_in_order)
+
+
+def enforce_order(form_class, fields_in_order):
+    """ Takes a list of fields used in a form_class and enforces the
+    order of those fields.
+
+    If not all fields in the form are given, the resulting order is undefined.
+
+    """
+
+    # XXX to make sure the field order of the existing class remains
+    # unchanged, we need to instantiate the class once (wtforms seems
+    # to do some housekeeping somehwere)
+    form_class()
+
+    class EnforcedOrderForm(form_class):
+        pass
+
+    processed = set()
+
     for counter, name in enumerate(fields_in_order, start=1):
         if name in processed:
             continue
 
-        getattr(MergedForm, name).creation_counter = counter
+        getattr(EnforcedOrderForm, name).creation_counter = counter
         processed.add(name)
 
-    return MergedForm
+    return EnforcedOrderForm
+
+
+def move_fields(form_class, fields, after):
+    """ Reorders the given fields (given by name) by inserting them directly
+    after the given field.
+
+    If ``after`` is None, the fields are moved to the end.
+
+    """
+
+    fields_in_order = []
+
+    for name, _ in utils.get_fields_from_class(form_class):
+        if name in fields:
+            continue
+
+        fields_in_order.append(name)
+
+        if name == after:
+            fields_in_order.extend(fields)
+
+    if after is None:
+        fields_in_order.extend(fields)
+
+    return enforce_order(form_class, fields_in_order)

onegov/form/tests/test_core.py

@@ -1,4 +1,4 @@
-from onegov.form import Form, merge_forms, with_options
+from onegov.form import Form, merge_forms, with_options, move_fields
 from wtforms import RadioField, StringField, TextAreaField, validators
 from wtforms.fields.html5 import EmailField
 from wtforms.validators import InputRequired
@@ -332,3 +332,16 @@ def is_valid_user(self):
     assert full.is_valid_name()
     assert full.is_valid_coordinate()
     assert full.is_valid_user()
+
+
+def test_move_fields():
+
+    class Test(Form):
+        a = StringField('a')
+        b = StringField('b')
+        c = StringField('c')
+
+    Moved = move_fields(Test, ['a'], None)
+
+    assert list(Test()._fields.keys()) == ['a', 'b', 'c']
+    assert list(Moved()._fields.keys()) == ['b', 'c', 'a']