formbar / docs / source / config.rst

Form configuration

The form will be configured using a XML definition. The configuration is basically splitted into two parts:

  1. The definition of the datamodel in the source directive.
  2. Definition and Layout of forms in forms.

The basic form configuration looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <!-- Define different entity types -->
   <!-- Define and layout a form -->
   <!-- Container holdig parts of a form definition -->

The :ref:`snippet` element is optional and just a helper.


The source directive defines the :ref:`entity` are available in your forms. An entity is defined only once in the source section. It will get referenced in the :ref:`form` directive later to build the forms.


A :ref:`entity` is a field definition. The entity is used to configure aspects of the datamodel the layout and behaviour of the field in the form.

Here is an example of an entity definition:

<entity id="f1" name="age" label="Age" type="integer" css="field" required="true">
    <renderer type="text"/>
    <help>This is a help text</help>
    <rule expr="$age ge 21" msg="Age must be greater than 21"/>

Entities can be marked as required or desired. Formed will generate automatically a :ref:`rule` for this field. Missing required fields will trigger an error on form validation. Desired fields will trigger a warning.

Entities can be marked as readonly. Readonly fields are renderer as simple text in the form displaying the current value of the field. Note, that readonly fields are not sent on submission! If you need the value if the form you will need to add an additional entity and render is with the hidden field renderer.

Each entity can optional have a :ref:`renderer`, :ref:`rule` or :ref:`help` element.

Attribute Description
id Used to refer to this entity in the form. Requiered. Must be unique.
name Used as name attribute in the rendered field. Defines the name of this attribute in the model.
label The field will be rendered with this label.
number A small number which is rendered in front of the label.
type Defines the python datatype which will be used on deserialisation of the submitted value. Defines the datatype of the model. Possible values are string (default), integer, float, date, datetime.
css Value will be rendered as class attribute in the rendered field.
expr Expression which is used to calculate the value of the field.
readonly Flag to indicate that the field should be rendered as readonly field. Default is false.
required Flag to indicate that the is a required field. Default is false.
desired Flag to indicate that the is a desired field. Default is false.


Rules are used to validate data in the form. Formed does already some basic validated on the submitted data depending on the configured data type in the :ref:`entity`. These checks are often already sufficient for most basic forms.

If you need more validation rules can be used to define additional checks. There are two types of rules. Rules which triggers errors, and rules which trigger a warning if the evaluation of the rule fails.

Rules are evaluated in the process of validation the submitted data. On validation formed will collect warning and errors and will rerender the form displaying them. If the form has errors the validation fails. Warnings are ok for validation.

Validation of rules can be done in differen modes. Rules with the mode pre are evaluation before the deserialisation of the submitted value occurs into the python data type of the field. In contrast rules with mode post are evaluation after the deserialisation happened.

Here is a example rule:

<rule expr="$age ge 21" msg="Age must be greater than 21" mode="post" triggers="warning"/>

Here you can see a example rule. The rule will check the value of field "age" ($age) is greater or equal that the value 21. The rule is evaluated in post mode. And will trigger a warning if the evaluation fails.

Attribute Description
expr Expression which is used to validate the value if the field.
msg The message which is displayed if the evaluation of the rule fails.
mode Point in validation when this rules gets evaluations. post (default) means after the deserialisation of the value and pre is before deserialisation.
triggers Flag which defines which type of message a the rule will trigger if the evaluation fails. Be be error (default) or warning.


The help block can be used to add some information to the field for the user. The help will be rendererd below the field in the form.


The renderer directive can be used to configure an alternative renderer to be used to render the field.

The default renderer is chosen depending on the datatype of the field and is a textfield for almost all normal datatypes. On relations (in SQLAlchemy mapped items) a selection field is used for the relations.

There are different types of renderers available coming with formed. But it is very easy to provide formed with your own custom renderer.


Use this renderer if you want to render the field as a textfield:

<renderer type="textarea" rows="20"/>
Attribute Description
rows Number of rows of the texteare. Default is 3.


The info field renderer is used to render the value of the entity as textual information. This renderer is usually used to display calculated values of the entity. See the expr attribute of the :ref:`Entity`. Appearance is same as a readonly field:

<renderer type="infofield"/>


The selection renderer is used to render a selection list fields. Such a field is capable to select multiple optiones. The renderer defines also the options which should be available in the dropdown menu. For SQLAlchemy mapped items the options are automatically determined from the underlying data model:

<renderer type="selection">
   <option value="1">Option 1</option>
   <option value="2">Option 2</option>
   <option value="3">Option 3</option>
Attribute Description
filter Expression which must evaluate to True if the option shoul be shown in the Dropdown.
ignore Another way to filter options. (Deprecated)


Filtering is only possible for SQLAlchemy mapped items.

Filtering can be done by defining a expression in the filter attribute. This expression is later evaluated by the rule system of formbar. The expression must evaluate to true and is evaluated for every option. The expression uses a special variable begining with %. Variables begining with % marks the name of an attribute of the current options item. The variable will be replaced by the value of the attribute of the current item in the option for every option before evaluating:

<renderer type="selection" filter="'foo' in %bar">

The ignore attribute offers another but deprecated way to filter options. It syntax differs from the filter expression. See source for more information.


The dropdown renderer is used to render dropdown fields. The renderer defines also the options which should be available in the dropdown menu. For SQLAlchemy mapped items the options are automatically determined from the underlying data model:

<renderer type="dropdown">
   <option value="1">Option 1</option>
   <option value="2">Option 2</option>
   <option value="3">Option 3</option>
Attribute Description
filter Expression which must evaluate to True if the option shoul be shown in the Dropdown.
ignore Another way to filter options. (Deprecated)


Filtering is only possible for SQLAlchemy mapped items.

See filtering section of the :ref:`dropdown` renderer.


The datepicker renderer has some Javascript functionality which lets the used pick the date from a calender. It also only allows valid date entries per keyboard:

<renderer type="datepicker"/>


The password renderer renderes a password field which hides the users input:

<renderer type="password"/>


The hidden field renderer is used to render a hidden field for the entity. No labels, helptexts or error messages will be renderer. The hidden field will also take care on relations for SQLAlchemy mapped items:

<renderer type="hidden"/>


The html renderer is used to render custom html code. This is usefull if you want to render generic text sections or insert images. Images will need a external source for the image file. The html renderer will render Javascript , Stylesheets and HTML code:

<renderer type="html">
   <p>You can include all valid html including images, lists etc.</p>
   <p><strong>Warning:</strong>Also JS can be included.</p>

Your custom code should be wrapped into a empty div node. Otherwise only the first child node of the renderer will be rendererd. The entity only needs the id attribute. If a label is provided, the label will be uses as some kind of header to the html part.


Use this renderer with caution as it may introduce a large security hole if users inject malicious javascript code into the form using the html renderer.


The form directive is the place where the form definition and layout happens.


You can define more than one form in one configuration. This gets very handy if you want to define different forms for differen purposes. Example: You have a form to create a new item with a reduced set of fields. Another form which has all fields included can be used to edit the item.

Forms are built by using references to the defined entities packed in some layout directives:

<form id="create" css="fooish" autocomplete="off" method="POST" action="" enctype="multipart/form-data">
Attribute Description
id Unique id of the field.
css The attribute will be added to the class attribute of the form.
autocomplete Flag to indicate if the form should be autocompleted by the browser. Defaults to on.
method HTTP method used to submit the data. Defaults to POST.
action URL where is submitted data is sent to. Default to the current URL.
enctype Encrytion used while sending the data. Defaults to application/x-www-form-urlencoded. Use multipart/form-data if you plan to submit file uploads.


Use pages if you want to divide your form into multiple pages. Pages are rendered as a separate outline of the form on the left site to navigate through the form pages.

Row, Col

Used to layout the form:

  <col width="8"></col>
  <col width="2"></col>
  <col width="2"></col>

The form is divided into 12 virtual cols. The width of each col is calculated automatically. A single in a row will have the full width of 12. For 2 cols in a row each col will have a width of 6 cols. If you define 3 cols each col will have a width of 4 and so on.

You can alternatively define the width of the col. If you provide the width of the col you need to take care that the sum of all cols in the row is 12 to not mess up the layout.

Rows and cols can be mixed. So rows can be in cols again.

Attribute Description
width Width of the col (1-12).


A fieldset can be used to group fields into a logical unit a fieldset will have a label which is rendered as a heading above the first field of the fieldset. Fieldsets can be nested to model some kind of hierarchy. Formbar supports up to three levels. The size of the font in the fieldset legend will be reduced a littlebit on every level.:

<fieldset label="1. Foo">
  <fieldset label="1.1 Bar">

A fieldset can include almost all other directives.

Attribute Description
label Label of the fieldset rendered as header.



Tables should not be used to layout the form!

Tables can be used to arrange your fields in a tabuluar form. This becomes handy in some situations e.g to build your own widget:

    <td width="70%">Number of humans in the world</td>
    <td><field ref="men"/></td>
    <td><field ref="women"/></td>
    <td><field ref="total"/></td>

Tables are usually used in the same way as :ref:`field` is used. Tables will take 100% of the available space. You can set the width attribute of the <td> field to configure the width of the columns.


A field in the form. The field only references an :ref:`Entity`:

<field ref="f1"/>
Attribute Description
ref id if the referenced :ref:`Entity`.


Conditional can be used to hide, or render form elements like fields, tables, fieldsets and text elements within the conditional as readonly elements.

If the condition must evaluate to true or false. If true, the elements are rendered normal. If the condition is false the effect is determined by the type of the conditional. On default the elements will be hidden completely. As alternative you can set the type of the conditional to "readonly". Currently only the types "hide" (default) and "readonly" are supported. Expample:

<if type="readonly" expr="$fieldname == 4">
    <field ref="r1"/>

In the example above the referenced field will be shown if the field in the form with the name "fieldname" has the value of 4. Else the element will be set to readonly and the element will have a lowered opacity.

Attribute Description
type Effect of the conditional if the condition evaluates to false. Defaults to hide.
expr The expression which will be evaluated.

Conditionals are evaluated using JavaScript on the client side. Formbar also needs to evaluate the conditional internal on validation to determine which values will be taken into account while validating. As result validation rules will not be applied for "hidden" fields.


Snippets are reusable parts of your form definiton. Snippets allow you to define parts of the form only once and use them in multiple forms. Example: If you want to use the same form to create and edit than you can define the form in a snippet and use it in the create and edit form:

<form id="foo">
  <snippet ref="s1"/>
<form id="bar">
  <snippet ref="s1"/>
<snippet id="s1">

Snippet needs to be in a form to get rendered. Snippets can reference other snippets using the ref attribute. Snippets are of great help if you want to reduced the effort of rearranging groups of elements in the form. But on the other side the can make the form quite complicated if you use them too much. Use them with care.

Attribute Description
id Unique id of the snippet
ref References the snippet with id.

Custom renderes

Write me!

External validators

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