Fields

This chapter describes the standard schema fields for Plone forms and content types.

The following tables show the most common field types for use in Forms and Dexterity Content Types. See schemas for information about how fields compose a schema for a form or content type data model.

Tip

In VS Code editor, you can install the Plone Snippets extension. This will give you snippets for most fields, widgets, and autoform directives in Python and XML based schemas.

Field properties

You can initialize fields by passing properties into their constructors. To avoid repeating the available properties for each field, we'll list them once here, grouped into the interfaces that describe them. You'll see those interfaces again in the tables below that describe the various field types. Refer to the table below to see what properties a particular interface implies.

Interface	Property	Type	Description
IField	title	int	The title of the field. Used in the widget.
	description	unicode	A description for the field. Used in the widget.
	required	bool	Whether or not the field is required. Used for form validation. The default is True.
	readonly	bool	Whether or not the field is read only. Default is False.
	default		The default value for the field. Used in forms and sometimes as a fallback value. Must be a valid value for the field if set. The default is None.
	defaultFactory		The default factory method for the field. Used in forms and sometimes as a fallback value. This is a name of a method which returns a dynamic default value.
	missing_value		A value that represents "this field is not set." Used by form validation. Defaults to None. For lists and tuples, it is sometimes useful to set this to an empty list or tuple.
IMinMaxLen	min_length	int	The minimum required length or minimum number of elements. Used for string, sequence, mapping, or set fields. Default is 0.
	max_length	int	The maximum allowed length or maximum number of elements. Used for string, sequence, mapping, or set fields. Default is None (no check).
IMinMax	min		The minimum allowed value. Must be a valid value for the field, for example, an int field should be an integer. Default is None (no check).
	max		The maximum allowed value. Must be a valid value for the field, for example an int field should be an integer. Default is None (no check).
ICollection	value_type		Another Field instance that describes the allowable values in a list, tuple, or other collection. Must be set for any collection field. One common usage is to set this to a Choice to model a multi-selection field with a vocabulary.
	unique	bool	Whether or not values in the collection must be unique. Usually not set directly. Use a Set or Frozenset to guarantee uniqueness in an efficient way.
IDict	key_type		Another Field instance that describes the allowable keys in a dictionary. Similar to the value_type of a collection. Must be a Set.
	value_type		Another Field instance that describes the allowable values in a dictionary. Similar to the value_type of a collection. Must be a Set.
IObject	schema	Interface	An interface that must be provided by any object stored in this field.
IRichText	default_mime_type	str	Default MIME type for the input text of a rich text field. Defaults to text/html.
	output_mime_type	str	Default output MIME type for the transformed value of a rich text field. Defaults to text/x-html-safe. There must be a transformation chain in the portal_transforms tool that can transform from the input value to the output value for the output property of the RichValue object to contain a value.
	allowed_mime_types	tuple	A list of allowed input MIME types. The default is None, in which case the site-wide settings from the Markup control panel will be used.

See IField interface and field implementation in zope.schema documentation for details.

Field types

The following tables describe the most commonly used field types, grouped by the module from which they can be imported.

Fields in zope.schema

Name	Type	Description	Properties
Choice	n/a	Used to model selection from a vocabulary, which must be supplied. Often used as the value_type of a selection field. The value type is the value of the terms in the vocabulary.	See Vocabularies.
Bytes	str	Used for binary data.	IField, IMinMaxLen
ASCII	str	ASCII text (multi-line).	IField, IMinMaxLen
BytesLine	str	A single line of binary data, in other words a Bytes with new lines disallowed.	IField, IMinMaxLen
ASCIILine	str	A single line of ASCII text.	IField, IMinMaxLen
Text	unicode	Unicode text (multi-line). Often used with a WYSIWYG widget, although the default is a text area.	IField, IMinMaxLen
TextLine	unicode	A single line of Unicode text.	IField, IMinMaxLen
Bool	bool	True or False.	IField
Int	int, long	An integer number. Both ints and longs are allowed.	IField, IMinMax
Float	float	A floating point number.	IField, IMinMax
Tuple	tuple	A tuple (non-mutable).	IField, ICollection, IMinMaxLen
List	list	A list.	IField, ICollection, IMinMaxLen
Set	set	A set.	IField, ICollection, IMinMaxLen
Frozenset	frozenset	A frozenset (non-mutable).	IField, ICollection, IMinMaxLen
Password	unicode	Stores a simple string, but implies a password widget.	IField, IMinMaxLen
Dict	dict	Stores a dictionary. Both key_type and value_type must be set to fields.	IField, IMinMaxLen, IDict
Datetime	datetime	Stores a Python datetime (not a Zope 2 DateTime).	IField, IMinMax
Date	date	Stores a Python date.	IField, IMinMax
Timedelta	timedelta	Stores a Python timedelta.	IField, IMinMax
SourceText	unicode	A text field intended to store source text, such as HTML or Python code.	IField, IMinMaxLen
Object	n/a	Stores a Python object that conforms to the interface given as the schema. There is no standard widget for this.	IField, IObject
URI	str	A URI (URL) string.	IField, MinMaxLen
Id	str	A unique identifier, either a URI or a dotted name.	IField, IMinMaxLen
DottedName	str	A dotted name string.	IField, IMinMaxLen
InterfaceField	Interface	A Zope interface.	IField
Decimal	Decimal	Stores a Python Decimal. Requires version 3.4 or later of zope.schema. Not available by default in Zope 2.10.	IField, IMinMax

Fields in plone.namedfile.field

See plone.namedfile and plone.formwidget.namedfile for more details.

Name	Type	Description	Properties
NamedFile	NamedFile	A binary uploaded file. Normally used with the widget from plone.formwidget.namedfile.	IField
NamedImage	NamedImage	A binary uploaded image. Normally used with the widget from plone.formwidget.namedfile.	IField
NamedBlobFile	NamedBlobFile	A binary uploaded file stored as a ZODB blob. Requires the blobs extra to plone.namedfile. Otherwise identical to NamedFile.	IField
NamedBlobImage	NamedBlobImage	A binary uploaded image stored as a ZODB blob. Requires the blobs extra to plone.namedfile. Otherwise identical to NamedImage.	IField

NamedBlobImage

The following example shows how to create an Image object, and attach the image file to it.

img_obj = api.content.create(
    container=ww_article,
    type="Image",
    id="test.jpg",
    image=NamedBlobImage(
        data=img_file,
        filename="test.jpg",
    )
)

Fields in z3c.relationfield.schema

See z3c.relationfield for more details.

Name	Type	Description	Properties
Relation	RelationValue	Stores a single RelationValue.	IField
RelationList	list	A List field that defaults to Relation as the value type	See List
RelationChoice	RelationValue	A Choice field intended to store RelationValues	See Choice

Fields in plone.app.textfield

See plone.app.textfield for more details.

Name	Type	Description	Properties
RichText	RichTextValue	Stores a RichTextValue, which encapsulates a raw text value, the source MIME type, and a cached copy of the raw text transformed to the default output MIME type.	IField, IRichText

The RichText field allows for alternative markups and content filtering. The following code sample shows how to create a schema with a RichText field.

from plone.app.textfield import RichText
from plone.supermodel import model

class ITestSchema(model.Schema):

    body = RichText(title="Body text")

The RichText field constructor can take the following arguments, in addition to the usual arguments for a Text field.

default_mime_type

A string representing the default MIME type of the input markup. This defaults to text/html.

output_mime_type

A string representing the default output MIME type. This defaults to text/x-html-safe, which is a Plone-specific MIME type that disallows certain tags. Use the HTML Filtering control panel in Plone to control the tags.

allowed_mime_types

A tuple of strings giving a vocabulary of allowed input MIME types. If this is None (the default), the allowable types will be restricted to those set in Plone's Markup control panel.

The default field can be set to either a Unicode object (in which case it will be assumed to be a string of the default MIME type) or a RichTextValue.

reStructuredText transformation

Below is an example of a field that allows StructuredText and reStructuredText, transformed to HTML by default.

from plone.app.textfield import RichText
from plone.supermodel import model

defaultBody = """\
Background
==========

Please fill this in

Details
-------

And this
"""

class ITestSchema(model.Schema):

    body = RichText(
        title="Body text",
        default_mime_type="text/x-rst",
        output_mime_type="text/x-html",
        allowed_mime_types=("text/x-rst", "text/structured",),
        default=defaultBody,
    )

RichTextValue

The RichText field usually does not store a string. Instead, it stores a RichTextValue object. This is an immutable object that has the following properties.

raw

A Unicode string with the original input markup.

mimeType

The MIME type of the original markup, for example, text/html or text/structured.

encoding

The default character encoding used when transforming the input markup. Most likely, this will be UTF-8.

raw_encoded

The raw input encoded in the given encoding.

outputMimeType

The MIME type of the default output, taken from the field at the time of instantiation.

output

A Unicode object representing the transformed output. If possible, this is cached persistently, until the RichTextValue is replaced with a new one (as happens when an edit form is saved, for example).

The storage of the RichTextValue object is optimized for the case where the transformed output will be read frequently (for example, on the view screen of the content object) and the raw value will be read infrequently (for example, on the edit screen). Because the output value is cached indefinitely, you will need to replace the RichTextValue object with a new one if any of the transformation parameters change. However, as we will see below, it is possible to apply a different transformation on demand, if you need to.

The code snippet below shows how a RichTextValue object can be constructed in code. In this case, we have a raw input string of type text/plain that will be transformed to a default output of text/html. Note that we would normally look up the default output type from the field instance.

from plone.app.textfield.value import RichTextValue

context.body = RichTextValue("Some input text", mimeType="text/html", outputMimeType="text/x-html-safe")

The standard widget used for a RichText field will correctly store this type of object for you, so it is rarely necessary to create one yourself.

RichText fields in templates

If you use a DisplayForm, the display widget for the RichText field will render the transformed output markup automatically. If you write TAL manually, you may try something like the following.

<div tal:content="structure context/body" />

This, however, will render a string as follows.

RichTextValue object. (Did you mean <attribute>.raw or <attribute>.output?)

The correct syntax is:

<div tal:content="structure context/body/output" />

This will render the cached, transformed output. This operation is approximately as efficient as rendering a simple Text field, since the transformation is only applied once, when the value is first saved.

Alternative transformations

Sometimes, you may want to invoke alternative transformations. Under the hood, the default implementation uses the portal_transforms tool to calculate a transform chain from the raw value's input MIME type to the desired output MIME type. If you need to write your own transforms, take a look at Changing Portal Transforms Settings via Python. This is abstracted behind an ITransformer adapter to allow alternative implementations.

To invoke a transformation in code, you can use the following syntax.

from plone.app.textfield.interfaces import ITransformer

transformer = ITransformer(context)
transformedValue = transformer(context.body, "text/plain")

The __call__() method of the ITransformer adapter takes a RichTextValue object and an output MIME type as parameters.

If you write a page template, there is an even more convenient syntax.

<div tal:content="structure context/@@text-transform/body/text/plain" />

The first traversal name segment gives the name of the field on the context (body in this case). The second and third segments give the output MIME type. If the MIME type is omitted, the default output MIME type will be used.

Note

Unlike the output property, the value is not cached, and so will be calculated each time the page is rendered.

Fields in plone.schema

See plone.schema versus zope.schema for more details.

Name	Type	Description	Properties
Email	str	A field containing an email address	IField, IMinMaxLen
JSON

Schema

With plone.autoform and plone.supermodel we can use directives to add information to the schema fields.

Protect a field with a permission

By default, fields are included in the form regardless of the user's permissions. Fields can be protected using the read_permission and write_permission directives. The read permission is checked when the field is in display mode, and the write permission is checked when the field is in input mode. The permission should be given with its Zope 3-style name, such as cmf.ManagePortal instead of Manage portal.

In this example, the secret field is protected by the cmf.ManagePortal permission as both a read and write permission. This means that in both display and input modes, the field will only be included in the form for users who have that permission:

from plone.supermodel import model
from plone.autoform import directives as form

class IMySchema(model.Schema):
    form.read_permission(secret="cmf.ManagePortal")
    form.write_permission(secret="cmf.ManagePortal")
    secret = schema.TextLine(
        title = "Secret",
        )

In supermodel XML, the directives are security:read-permission and security:write-permission:

<field type="zope.schema.TextLine"
        name="secret"
        security:read-permission="cmf.ManagePortal"
        security:write-permission="cmf.ManagePortal">
    <title>Secret</title>
</field>