**Note**: The`style` argument replaces the old-style version 2.x`widget` keyword argument. Because REST framework 3 now uses templated HTML form generation, the`widget` option that was used to support Django built-in widgets can no longer be supported. Version 3.1 is planned to include public API support for customizing HTML form generation.

**Note**: The`style` argument replaces the old-style version 2.x`widget` keyword argument. Because REST framework 3 now uses templated HTML form generation, the`widget` option that was used to support Django built-in widgets can no longer be supported. Version 3.3 is planned to include public API support for customizing HTML form generation.

-`choices` - A list of valid values, or a list of`(key, display_name)` tuples.

-`allow_blank` - If set to`True` then the empty string should be considered a valid value. If set to`False` then the empty string is considered invalid and will raise a validation error. Defaults to`False`.

-`html_cutoff` - If set this will be the maximum number of choices that will be displayed by a HTML select drop down. Can be used to ensure that automatically generated ChoiceFields with very large possible selections do not prevent a template from rendering. Defaults to`None`.

-`html_cutoff_text` - If set this will display a textual indicator if the maximum number of items have been cutoff in an HTML select drop down. Defaults to`"More than {count} items…"`

Both the`allow_blank` and`allow_null` are valid options on`ChoiceField`, although it is highly recommended that you only use one and not both.`allow_blank` should be preferred for textual choices, and`allow_null` should be preferred for numeric or other non-textual choices.

-`choices` - A list of valid values, or a list of`(key, display_name)` tuples.

-`allow_blank` - If set to`True` then the empty string should be considered a valid value. If set to`False` then the empty string is considered invalid and will raise a validation error. Defaults to`False`.

-`html_cutoff` - If set this will be the maximum number of choices that will be displayed by a HTML select drop down. Can be used to ensure that automatically generated ChoiceFields with very large possible selections do not prevent a template from rendering. Defaults to`None`.

-`html_cutoff_text` - If set this will display a textual indicator if the maximum number of items have been cutoff in an HTML select drop down. Defaults to`"More than {count} items…"`

As with`ChoiceField`, both the`allow_blank` and`allow_null` options are valid, although it is highly recommended that you only use one and not both.`allow_blank` should be preferred for textual choices, and`allow_null` should be preferred for numeric or other non-textual choices.

When using the`ModelSerializer` class, serializer fields and relationships will be automatically generated for you. Inspecting these automatically generated fields can be a useful tool for determining how to customize the relationship style.

When rendered in the browsable API relational fields will default to only displaying a maximum of 1000 selectable items. If more items are present then a disabled option with "More than 1000 items…" will be displayed.

This behavior is intended to prevent a template from being unable to render in an acceptable timespan due to a very large number of relationships being displayed.

There are two keyword arguments you can use to control this behavior:

-`html_cutoff` - If set this will be the maximum number of choices that will be displayed by a HTML select drop down. Set to`None` to disable any limiting. Defaults to`1000`.

-`html_cutoff_text` - If set this will display a textual indicator if the maximum number of items have been cutoff in an HTML select drop down. Defaults to`"More than {count} items…"`

In cases where the cutoff is being enforced you may want to instead use a plain input field in the HTML form. You can do so using the`style` keyword argument. For example:

Note that reverse relationships are not automatically included by the`ModelSerializer` and`HyperlinkedModelSerializer` classes. To include a reverse relationship, you must explicitly add it to the fields list. For example:

defiter_options(grouped_choices):

defiter_options(grouped_choices,cutoff=None,cutoff_text=None):

def__init__(self,value,display_text):

def__init__(self,value,display_text,disabled=False):

self.value=value

self.display_text=display_text

self.disabled=disabled

forkey,valueingrouped_choices.items():

ifcutoffandcount>=cutoff:

ifisinstance(value,dict):

yieldStartOptionGroup(label=key)

forsub_key,sub_valueinvalue.items():

ifcutoffandcount>=cutoff:

yieldOption(value=sub_key,display_text=sub_value)

yieldEndOptionGroup()

else:

yieldOption(value=key,display_text=value)

ifcutoffandcount>=cutoffandcutoff_text:

cutoff_text=cutoff_text.format(count=cutoff)

yieldOption(value='n/a',display_text=cutoff_text,disabled=True)

classCreateOnlyDefault(object):

default_error_messages= {

'invalid_choice':_('"{input}" is not a valid choice.')

}

html_cutoff_text=_('More than {count} items...')

def__init__(self,choices,**kwargs):

self.grouped_choices=to_choices_dict(choices)

self.choices=flatten_choices_dict(self.grouped_choices)

self.html_cutoff=kwargs.pop('html_cutoff',self.html_cutoff)

self.html_cutoff_text=kwargs.pop('html_cutoff_text',self.html_cutoff_text)

returniter_options(self.grouped_choices)

returniter_options(

self.grouped_choices,

cutoff=self.html_cutoff,

cutoff_text=self.html_cutoff_text

)

classMultipleChoiceField(ChoiceField):

classRelatedField(Field):

html_cutoff_text=_('More than {count} items...')

def__init__(self,**kwargs):

self.queryset=kwargs.pop('queryset',self.queryset)

self.html_cutoff=kwargs.pop('html_cutoff',self.html_cutoff)

self.html_cutoff_text=kwargs.pop('html_cutoff_text',self.html_cutoff_text)

assertself.querysetisnotNoneorkwargs.get('read_only',None), (

returnself.choices

defiter_options(self):

returniter_options(self.grouped_choices)

returniter_options(

self.grouped_choices,

cutoff=self.html_cutoff,

cutoff_text=self.html_cutoff_text

)

defdisplay_value(self,instance):

returnsix.text_type(instance)

'not_a_list':_('Expected a list of items but got type "{input_type}".'),

'empty':_('This list may not be empty.')

}

html_cutoff_text=_('More than {count} items...')

def__init__(self,child_relation=None,*args,**kwargs):

self.child_relation=child_relation

self.allow_empty=kwargs.pop('allow_empty',True)

self.html_cutoff=kwargs.pop('html_cutoff',self.html_cutoff)

self.html_cutoff_text=kwargs.pop('html_cutoff_text',self.html_cutoff_text)

assertchild_relationisnotNone,'`child_relation` is a required argument.'

super(ManyRelatedField,self).__init__(*args,**kwargs)

self.child_relation.bind(field_name='',parent=self)

returnself.choices

defiter_options(self):

returniter_options(self.grouped_choices)

returniter_options(

self.grouped_choices,

cutoff=self.html_cutoff,

cutoff_text=self.html_cutoff_text

)

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% endfor %}

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% empty %}

<option>{{ no_items }}</option>

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% endfor %}

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% empty %}

<option>{{ no_items }}</option>

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.value ==field.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% endfor %}

{% elif select.end_option_group %}

{% else %}

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}>{{ select.display_text }}</option>

<optionvalue="{{ select.value }}"{%ifselect.valueinfield.value%}selected{%endif%}{%ifselect.disabled%}disabled{%endif%}>{{ select.display_text }}</option>

{% endif %}

{% empty %}

<option>{{ no_items }}</option>