.. _aiorest-ws-fields:

Serializer fields
=================

.. currentmodule:: aiorest_ws.db.orm.fields

Serializer fields handle converting between primitive values and internal datatypes. They also
deal with validating input values, as well as retrieving and setting the values from their parent
objects.

**Note**: The serializer fields are declared in ``fields.py``, but by convention you should import
them using ``from aiorest_ws.db.orm.django import serializers`` or ``from aiorest_ws.db.orm.
sqlalchemy import serializers`` and refer to fields as ``serializers.<FieldName>``.

Core arguments
--------------
Each serializer field class constructor takes at least these arguments. Some Field classes take
additional, field-specific arguments, but the following should always be accepted:

- ``read_only``

Read-only fields are included in the API output, but should not be included in the input during
create or update operations. Any 'read_only' fields that are incorrectly included in the serializer
input will be ignored.

Set this to ``True`` to ensure that the field is used when serializing a representation, but is not
used when creating or updating an instance during deserialization.

Defaults to ``False``

- ``write_only``

Set this to ``True`` to ensure that the field may be used when updating or creating an instance,
but is not included when serializing the representation.

Defaults to ``False``

- ``required``

Normally an error will be raised if a field is not supplied during deserialization. Set to false if
this field is not required to be present during deserialization.

Setting this to ``False`` also allows the object attribute or dictionary key to be omitted from
output when serializing the instance. If the key is not present it will simply not be included in
the output representation.

Defaults to ``True``.

- ``allow_null``

Normally an error will be raised if ``None`` is passed to a serializer field. Set this keyword
argument to ``True`` if ``None`` should be considered a valid value.

Defaults to ``False``

- ``default``

If set, this gives the default value that will be used for the field if no input value is supplied.
If not set the default behaviour is to not populate the attribute at all.

The ``default`` is not applied during partial update operations. In the partial update case only
fields that are provided in the incoming data will have a validated value returned.

May be set to a function or other callable, in which case the value will be evaluated each time it
is used. When called, it will receive no arguments. If the callable has a ``set_context`` method,
that will be called each time before getting the value with the field instance as only argument.
This works the same way as for validators.

Note that setting a ``default`` value implies that the field is not required. Including both the
``default`` and ``required`` keyword arguments is invalid and will raise an error.

- ``source``

The name of the attribute that will be used to populate the field. May be a method that only takes
a ``self`` argument, such as ``URLField(source='get_absolute_url')``, or may use dotted notation
to traverse attributes, such as ``EmailField(source='user.email')``.

The value ``source='*'`` has a special meaning, and is used to indicate that the entire object
should be passed through to the field. This can be useful for creating nested representations, or
for fields which require access to the complete object in order to determine the output
representation.

Defaults to the name of the field.

- ``validators``

A list of validator functions which should be applied to the incoming field input, and which either
raise a validation error or simply return. Validator functions should typically raise
``serializers.ValidationError``.

- ``error_messages``

A dictionary of error codes to error messages.

- ``label``

A short text string that may be used as the name of the field in HTML form fields or other
descriptive elements.

- ``initial``

A value that should be used for pre-populating the value of HTML form fields. You may pass a
callable to it, just as you may do with any regular Django ``Field``. For example:

.. code-block:: python

    import datetime
    from aiorest_ws.db.orm.django import serializers

    class ExampleSerializer(serializers.Serializer):
        day = serializers.DateField(initial=datetime.date.today)



Custom fields
-------------
If you want to create a custom field, you'll need to subclass :class:`AbstractField` and then
override either one or both of the ``.to_representation()`` and ``.to_internal_value()`` methods.
These two methods are used to convert between the initial datatype, and a primitive, serializable
datatype. Primitive datatypes will typically be any of a number, string, boolean, ``date`` /
``time`` / ``datetime`` or ``None``. They may also be any list or dictionary like object that only
contains other primitive objects. Other types might be supported, depending on the renderer that
you are using.

The ``.to_representation()`` method is called to convert the initial datatype into a primitive,
serializable datatype.

The ``to_internal_value()`` method is called to restore a primitive datatype into its internal
python representation. This method should raise a :class:`ValidationError` if the data is invalid.

For example:

.. code-block:: python

    from aiorest_ws.db.orm.abstract import AbstractField

    class Color(object):
        """
        A color represented in the RGB colorspace.
        """
        def __init__(self, red, green, blue):
            assert(red >= 0 and green >= 0 and blue >= 0)
            assert(red < 256 and green < 256 and blue < 256)
            self.red, self.green, self.blue = red, green, blue

    class ColorField(AbstractField):
        """
        Color objects are serialized into 'rgb(#, #, #)' notation.
        """
        default_error_messages = {
            'incorrect_type': 'Incorrect type. Expected a string, but got {input_type}',
            'incorrect_format': 'Incorrect format. Expected `rgb(#,#,#)`.',
            'out_of_range': 'Value out of range. Must be between 0 and 255.'
        }

        def to_representation(self, obj):
            return "rgb(%d, %d, %d)" % (obj.red, obj.green, obj.blue)

        def to_internal_value(self, data):
            if not isinstance(data, six.text_type):
                self.raise_error('incorrect_type', input_type=type(data).__name__)

            if not re.match(r'^rgb\([0-9]+,[0-9]+,[0-9]+\)$', data):
                self.raise_error('incorrect_format')

            data = data.strip('rgb(').rstrip(')')
            red, green, blue = [int(col) for col in data.split(',')]

            if any([col > 255 or col < 0 for col in (red, green, blue)]):
                self.raise_error('out_of_range')

            return Color(red, green, blue)


The ``.raise_error()`` method is a shortcut for raising :class:`ValidationError` that takes a
message string from the ``error_messages`` dictionary.

Supported fields
----------------

BigIntegerField
^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy ORM*

An big integer representation.

Corresponds to ``sqlalchemy.types.BigInteger``.

**Signature**: ``BigIntegerField()``

Have the same functionality as :class:`IntegerField` class. By default an instance of
:class:`BigIntegerField` class has the ``MAX_BIG_INTEGER`` attribute which is storing
``9223372036854775807`` value and used as the ``max_value`` argument. For the ``min_value``
argument used ``-MAX_BIG_INTEGER - 1`` value.

BooleanField
^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A boolean representation.

When using HTML encoded form input be aware that omitting a value will always be treated as setting
a field to ``False``, even if it has a ``default=True`` option specified. This is because HTML
checkbox inputs represent the unchecked state by omitting the value, so aiorest-ws framework treats
omission as if it is an empty checkbox input.

Corresponds to ``django.db.models.fields.BooleanField`` and ``sqlalchemy.types.Boolean``.

**Signature**: ``BooleanField()``

CharField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A text representation. Optionally validates the text to be shorter than ``max_length`` and longer
than ``min_length``.

Corresponds to ``django.db.models.fields.CharField``, ``django.db.models.fields.TextField``,
, ``sqlalchemy.types.Text``, ``sqlalchemy.types.Unicode``, ``sqlalchemy.types.UnicodeText``.

**Signature**: ``CharField(max_length=None, min_length=None, allow_blank=False, trim_whitespace=True)``

- ``max_length`` - Validates that the input contains no more than this number of characters.
- ``min_length`` - Validates that the input contains no fewer than this number of characters.
- ``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``.
- ``trim_whitespace`` - If set to ``True`` then leading and trailing whitespace is trimmed. Defaults
  to ``True``.

The ``allow_null`` option is also available for string fields, although its usage is discouraged in
favor of ``allow_blank``. It is valid to set both ``allow_blank=True`` and ``allow_null=True``, but
doing so means that there will be two differing types of empty value permissible for string
representations, which can lead to data inconsistencies and subtle application bugs.

ChoiceField and EnumField
^^^^^^^^^^^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A field that can accept a value out of a limited set of choices.

Used by :class:`ModelSerializer` to automatically generate fields if the corresponding model field
includes a ``choices=…`` argument.

**Signature**: ``ChoiceField(choices)`` or ``EnumField(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``.

Both the ``allow_blank`` and ``allow_null`` are valid options on :class:`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.

DateField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A date representation.

Corresponds to ``django.db.models.fields.DateField`` and ``sqlalchemy.types.Date``.

**Signature**: ``DateField(format=api_settings.DATE_FORMAT, input_formats=None)``

- ``format`` - A string representing the output format. If not specified, this defaults to the same
  value as the ``DATE_FORMAT`` settings key, which will be ``'iso-8601'`` unless set. Setting to a
  format string indicates that ``to_representation`` return values should be coerced to string
  output. Format strings are described below. Setting this value to ``None`` indicates that Python
  ``date`` objects should be returned by ``to_representation``. In this case the date encoding will be
  determined by the renderer.
- ``input_formats`` - A list of strings representing the input formats which may be used to parse
  the date. If not specified, the ``DATE_INPUT_FORMATS`` setting will be used, which defaults to
  ``['iso-8601']``.

DateField format strings
~~~~~~~~~~~~~~~~~~~~~~~~
Format strings may either be `Python strftime formats <https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior/>`_
which explicitly specify the format, or the special string ``'iso-8601'``, which indicates that
`ISO 8601 <https://www.w3.org/TR/NOTE-datetime>`_ style dates should be used. (eg ``'2013-01-29'``)

DateTimeField
^^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A date and time representation.

Corresponds ``to django.db.models.fields.DateTimeField`` and ``sqlachemy.types.DateTime``.

**Signature**: ``DateTimeField(format=api_settings.DATETIME_FORMAT, input_formats=None)``

- ``format`` - A string representing the output format. If not specified, this defaults to the same
  value as the ``DATETIME_FORMAT`` settings key, which will be ``'iso-8601'`` unless set. Setting
  to a format string indicates that ``to_representation`` return values should be coerced to string
  output. Format strings are described below. Setting this value to ``None`` indicates that Python
  ``datetime`` objects should be returned by ``to_representation``. In this case the datetime
  encoding will be determined by the renderer.
- ``input_formats`` - A list of strings representing the input formats which may be used to parse
  the date. If not specified, the ``DATETIME_INPUT_FORMATS`` setting will be used, which defaults
  to ``['iso-8601']``.

DateTimeField format strings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Format strings may either be `Python strftime formats <https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior/>`_
which explicitly specify the format, or the special string ``'iso-8601'``, which indicates that
`ISO 8601 <https://www.w3.org/TR/NOTE-datetime>`_ style datetimes should be used. (eg ``'2013-01-29T12:34:56.000000Z'``)

When a value of ``None`` is used for the format ``datetime`` objects will be returned by
``to_representation`` and the final output representation will determined by the renderer class.

In the case of JSON this means the default datetime representation uses the
`ECMA 262 date time string specification <http://ecma-international.org/ecma-262/5.1/#sec-15.9.1.15>`_.
This is a subset of ISO 8601 which uses millisecond precision, and includes the 'Z' suffix for the
UTC timezone, for example: ``2013-01-29T12:34:56.123Z``.

auto_now and auto_now_add model fields
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When using :class:`ModelSerializer` or :class:`HyperlinkedModelSerializer`, note that any model
fields with ``auto_now=True`` or ``auto_now_add=True`` will use serializer fields that are
``read_only=True`` by default.

If you want to override this behavior, you'll need to declare the :class:`DateTimeField` explicitly
on the serializer. For example:

.. code-block:: python

    class CommentSerializer(serializers.ModelSerializer):
        created = serializers.DateTimeField()

        class Meta:
            model = Comment

DecimalField
^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A decimal representation, represented in Python by a ``Decimal`` instance.

Corresponds to ``django.db.models.fields.DecimalField`` and ``sqlalchemy.types.Numeric``.

**Signature**: DecimalField(max_digits, decimal_places, coerce_to_string=None, max_value=None, min_value=None)

- ``max_digits`` - The maximum number of digits allowed in the number. Note that this number must
  be greater than or equal to decimal_places.
- ``decimal_places`` - The number of decimal places to store with the number.
- ``coerce_to_string`` - Set to ``True`` if string values should be returned for the representation,
  or ``False`` if ``Decimal`` objects should be returned. Defaults to the same value as the
  ``COERCE_DECIMAL_TO_STRING`` settings key, which will be ``True`` unless overridden. If ``Decimal``
  objects are returned by the serializer, then the final output format will be determined by the
  renderer. Note that setting ``localize`` will force the value to ``True``.
- ``max_value`` - Validate that the number provided is no greater than this value.
- ``min_value`` - Validate that the number provided is no less than this value.
- ``localize`` - Set to ``True`` to enable localization of input and output based on the current
  locale. This will also force ``coerce_to_string`` to ``True``. Defaults to ``False``.

Example usage
~~~~~~~~~~~~~
To validate numbers up to 999 with a resolution of 2 decimal places, you would use:

.. code-block:: python

    serializers.DecimalField(max_digits=5, decimal_places=2)

And to validate numbers up to anything less than one billion with a resolution of 10 decimal places:

.. code-block:: python

    serializers.DecimalField(max_digits=19, decimal_places=10)

This field also takes an optional argument, ``coerce_to_string``. If set to ``True`` the
representation will be output as a string. If set to ``False`` the representation will be left as a
``Decimal`` instance and the final representation will be determined by the renderer.

If unset, this will default to the same value as the ``COERCE_DECIMAL_TO_STRING`` setting, which is
``True`` unless set otherwise.

DictField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A field class that validates a dictionary of objects. The keys in ``DictField`` are always assumed
to be string values.

**Signature**: ``DictField(child)``

- ``child`` - A field instance that should be used for validating the values in the dictionary. If
  this argument is not provided then values in the mapping will not be validated.

For example, to create a field that validates a mapping of strings to strings, you would write
something like this:

.. code-block:: python

    document = DictField(child=CharField())

You can also use the declarative style, as with ``ListField``. For example:

.. code-block:: python

    class DocumentField(DictField):
        child = CharField()


DurationField
^^^^^^^^^^^^^
*Supported by: Django ORM*

A Duration representation.

Corresponds to ``django.db.models.fields.DurationField``.

The ``validated_data`` for these fields will contain a ``datetime.timedelta`` instance. The
representation is a string following this format ``'[DD] [HH:[MM:]]ss[.uuuuuu]'``.

**Signature**: ``DurationField()``

EmailField
^^^^^^^^^^
*Supported by: Django ORM*

A text representation, validates the text to be a valid e-mail address.

Corresponds to ``django.db.models.fields.EmailField``.

**Signature**: ``EmailField(max_length=None, min_length=None, allow_blank=False)``

FileField
^^^^^^^^^
*Supported by: Django ORM*

A file representation. Performs Django's standard FileField validation.

Corresponds to ``django.forms.fields.FileField``.

``Signature``: ``FileField(max_length=None, allow_empty_file=False, use_url=UPLOADED_FILES_USE_URL)``

- ``max_length`` - Designates the maximum length for the file name.
- ``allow_empty_file`` - Designates if empty files are allowed.
- ``use_url`` - If set to ``True`` then URL string values will be used for the output representation.
  If set to ``False`` then filename string values will be used for the output representation.
  Defaults to the value of the ``UPLOADED_FILES_USE_URL`` settings key, which is ``True`` unless
  set otherwise.

FilePathField
^^^^^^^^^^^^^
*Supported by: Django ORM*

A field whose choices are limited to the filenames in a certain directory on the filesystem.

Corresponds to ``django.forms.fields.FilePathField``.

**Signature**: ``FilePathField(path, match=None, recursive=False, allow_files=True, allow_folders=False, required=None, **kwargs)``

- ``path`` - The absolute filesystem path to a directory from which this FilePathField should get its choice.
- ``match`` - A regular expression, as a string, that FilePathField will use to filter filenames.
- ``recursive`` - Specifies whether all subdirectories of path should be included. Default is ``False``.
- ``allow_files`` - Specifies whether files in the specified location should be included. Default is
  ``True``. Either this or ``allow_folders`` must be ``True``.
- ``allow_folders`` - Specifies whether folders in the specified location should be included. Default
  is ``False``. Either this or ``allow_files`` must be ``True``.

FloatField
^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A floating point representation.

Corresponds to ``django.db.models.fields.FloatField`` and ``sqlalchemy.types.Float``.

**Signature**: ``FloatField(max_value=None, min_value=None)``

- ``max_value`` - Validate that the number provided is no greater than this value.
- ``min_value`` - Validate that the number provided is no less than this value.

HStoreField
^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

An HStoreField which is supported by PostregSQL database.

**Signature**: ``HStoreField()``

*Note*: This field has the same functionality as the :class:`DictField` field, except that for this
field already have specified ``child`` argument as ``CharField(allow_blank=True)``.

IPAddressField
^^^^^^^^^^^^^^
*Supported by: Django ORM*

A field that ensures the input is a valid IPv4 or IPv6 string.

Corresponds to ``django.forms.fields.IPAddressField`` and ``django.forms.fields.GenericIPAddressField``.

**Signature**: ``IPAddressField(protocol='both', unpack_ipv4=False, **options)``

- ``protocol`` - Limits valid inputs to the specified protocol. Accepted values are 'both'
  (default), 'IPv4' or 'IPv6'. Matching is case insensitive.
- ``unpack_ipv4`` - Unpacks IPv4 mapped addresses like ::ffff:192.0.2.1. If this option is enabled
  that address would be unpacked to 192.0.2.1. Default is disabled. Can only be used when protocol
  is set to 'both'.

ImageField
^^^^^^^^^^
*Supported by: Django ORM*

An image representation. Validates the uploaded file content as matching a known image format.

Corresponds to ``django.forms.fields.ImageField``.

**Signature**: ``ImageField(max_length=None, allow_empty_file=False, use_url=UPLOADED_FILES_USE_URL)``

- ``max_length`` - Designates the maximum length for the file name.
- ``allow_empty_file`` - Designates if empty files are allowed.
- ``use_url`` - If set to ``True`` then URL string values will be used for the output
  representation. If set to ``False`` then filename string values will be used for the output
  representation. Defaults to the value of the ``UPLOADED_FILES_USE_URL`` settings key, which is
  ``True`` unless set otherwise.

Requires either the ``Pillow`` package or ``PIL`` package. The ``Pillow`` package is recommended,
as ``PIL`` is no longer actively maintained.

IntegerField
^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

An integer representation.

Corresponds to ``django.db.models.fields.IntegerField``, ``django.db.models.fields.SmallIntegerField``,
``django.db.models.fields.PositiveIntegerField``, ``django.db.models.fields.PositiveSmallIntegerField`` and
``sqlalchemy.types.Integer``.

**Signature**: ``IntegerField(max_value=None, min_value=None)``

- ``max_value`` - Validate that the number provided is no greater than this value.
- ``min_value`` - Validate that the number provided is no less than this value.

IntervalField
^^^^^^^^^^^^^
*Supported by: SQLAlchemy ORM*

An ``datetime.timedelta`` object representation.

Corresponds to ``sqlalchemy.types.Interval``.

**Signature**: ``IntervalField(display="minimal", separator=", ")``

- ``display`` - Determines a transform method from ``datetime.timedelta`` instances to human-readable strings:
    - ``sql`` - Returns timedelta in ``"<days> <hours>:<minutes>:<seconds>"`` format. (eg ``"5 20:32:01"``)
    - ``iso8601`` - Returns timedelta in `ISO 8601 <https://www.w3.org/TR/NOTE-datetime>`_ format.
    - ``minimal`` - Returns timeldeta in ``"<weeks>w, <days>d, <hours>h, <minutes>m,
      <seconds>s"`` format. Used by default. (eg ``"8h, 7m, 15s"``)
    - ``short`` - Returns timeldeta in ``"<weeks> wks, <days> days, <hours> hrs, <minutes> min,
      <seconds> sec"`` format. Used by default. (eg ``"2 wks, 9 day, 15 hrs"``)
    - ``long`` - Returns timedelta in ``"<weeks> weeks, <days> days, <hours> hours, <minutes> minutes,
      <seconds> seconds"`` format. Used by default. (eg ``"5 days, 8 hours, 10 minutes"``)
- ``separator`` - Default is ``", "``.

JSONField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A field class that validates that the incoming data structure consists of valid JSON primitives. In
its alternate binary mode, it will represent and validate JSON-encoded binary strings.

**Signature**: ``JSONField(binary)``

- ``binary`` - If set to ``True`` then the field will output and validate a JSON encoded string,
  rather than a primitive data structure. Defaults to ``False``.

LargeBinaryField
^^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy ORM*

A field class for a large binary byte data.

Corresponds to ``sqlalchemy.types.LargeBinary``.

**Signature**: ``LargeBinaryField(length=250)``

- ``length`` - If specified, then apply a validator on the passed binary by length. And if a length
  of this data if greater than ``length`` raises a validation error. Default is ``None``.

ListField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A field class that validates a list of objects.

**Signature**: ``ListField(child)``

- ``child`` - A field instance that should be used for validating the objects in the list. If this
  argument is not provided then objects in the list will not be validated.

For example, to validate a list of integers you might use something like the following:

.. code-block:: python

    scores = serializers.ListField(
       child=serializers.IntegerField(min_value=0, max_value=100)
    )

The ListField class also supports a declarative style that allows you to write reusable list field
classes.

.. code-block:: python

    class StringListField(serializers.ListField):
        child = serializers.CharField()

We can now reuse our custom :class:`StringListField` class throughout our application, without
having to provide a ``child`` argument to it.

ModelField
^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A generic field that can be tied to any arbitrary model field. The :class:`ModelField` class
delegates the task of serialization/deserialization to its associated model field. This field can
be used to create serializer fields for custom model fields, without having to create a new custom
serializer field.

This field is used by :class:`ModelSerializer` to correspond to custom model field classes.

**Signature**: ``ModelField(model_field=<Django ModelField instance>)``

The :class:`ModelField` class is generally intended for internal use, but can be used by your API
if needed. In order to properly instantiate a :class:`ModelField`, it must be passed a field that
is attached to an instantiated model. For example:

.. code-block:: python

    ModelField(model_field=MyModel()._meta.get_field('custom_field'))

MultipleChoiceField
^^^^^^^^^^^^^^^^^^^
*Supported by: Django ORM*

A field that can accept a set of zero, one or many values, chosen from a limited set of choices.
Takes a single mandatory argument. ``to_internal_value`` returns a ``set`` containing the selected
values.

**Signature**: ``MultipleChoiceField(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``.

As with :class:`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.

NullBooleanField
^^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A boolean representation that also accepts ``None`` as a valid value.

Corresponds to ``django.db.models.fields.NullBooleanField`` and ``sqlalchemy.types.Boolean``

**Signature**: ``NullBooleanField()``

PickleField
^^^^^^^^^^^
*Supported by: SQLAlchemy ORM*

A field class for Python objects, which are serialized using ``pickle`` module.

Corresponds to ``sqlalchemy.types.TypeDecorator``.

**Signature**: ``PickleField()``

*Note*: If field has not taken a data as the ``bytes`` type in `to_internal_value` method, then
raises a validation error.

ReadOnlyField
^^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A field class that simply returns the value of the field without modification.

This field is used by default with :class:`ModelSerializer` when including field names that relate
to an attribute rather than a model field.

**Signature**: ``ReadOnlyField()``

For example, if ``is_produced`` was a property on the ``Car`` model, then the following serializer
would automatically generate it as a :class:`ReadOnlyField`:

.. code-block:: python

    class CarSerializer(serializers.ModelSerializer):
        class Meta:
            model = Car
            fields = ('id', 'model', 'manufacturer', 'is_produced')

RegexField
^^^^^^^^^^
*Supported by: Django ORM*

A text representation, that validates the given value matches against a certain regular expression.

Corresponds to ``django.forms.fields.RegexField``.

**Signature**: ``RegexField(regex, max_length=None, min_length=None, allow_blank=False)``

The mandatory ``regex`` argument may either be a string, or a compiled python regular expression
object.

Uses Django's ``django.core.validators.RegexValidator`` for validation.

SerializerMethodField
^^^^^^^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

This is a read-only field. It gets its value by calling a method on the serializer class it is
attached to. It can be used to add any sort of data to the serialized representation of your object.

**Signature**: ``SerializerMethodField(method_name=None)``

- ``method_name`` - The name of the method on the serializer to be called. If not included this
  defaults to ``get_<field_name>``.

The serializer method referred to by the method_name argument should accept a single argument
(in addition to self), which is the object being serialized. It should return whatever you want to
be included in the serialized representation of the object. For example:

.. code-block:: python

    from django.contrib.auth.models import User
    from django.utils.timezone import now
    from aiorest_ws.db.orm.django import serializers

    class UserSerializer(serializers.ModelSerializer):
        days_since_joined = serializers.SerializerMethodField()

        class Meta:
            model = User

        def get_days_since_joined(self, obj):
            return (now() - obj.date_joined).days

SlugField
^^^^^^^^^
*Supported by: Django ORM*

A :class:`RegexField` that validates the input against the pattern ``[a-zA-Z0-9_-]+``.

Corresponds to ``django.db.models.fields.SlugField``.

**Signature**: ``SlugField(max_length=50, min_length=None, allow_blank=False)``

SmallIntegerField
^^^^^^^^^^^^^^^^^
*Supported by: SQLAlchemy ORM*

An big integer representation.

Corresponds to ``sqlalchemy.types.SmallInteger``.

**Signature**: ``SmallIntegerField()``

Have the same functionality as :class:`IntegerField` class. By default an instance of
:class:`SmallIntegerField` class has the ``MAX_SMALL_INTEGER`` attribute which is storing
``32767`` value and used as the ``max_value`` argument. For the ``min_value`` argument used
``-MAX_SMALL_INTEGER - 1`` value.

TimeField
^^^^^^^^^
*Supported by: SQLAlchemy and Django ORMs*

A time representation.

Corresponds to ``django.db.models.fields.TimeField`` or ``sqlalchemy.types.Time``.

**Signature**: ``TimeField(format=api_settings.TIME_FORMAT, input_formats=None)``

- ``format`` - A string representing the output format. If not specified, this defaults to the same
  value as the ``TIME_FORMAT`` settings key, which will be ``'iso-8601'`` unless set. Setting to a
  format string indicates that ``to_representation`` return values should be coerced to string
  output. Format strings are described below. Setting this value to ``None`` indicates that Python
  ``time`` objects should be returned by ``to_representation``. In this case the time encoding will
  be determined by the renderer.
- ``input_formats`` - A list of strings representing the input formats which may be used to parse
  the date. If not specified, the ``TIME_INPUT_FORMATS`` setting will be used, which defaults to
  ``['iso-8601']``.

TimeField format strings
~~~~~~~~~~~~~~~~~~~~~~~~
Format strings may either be `Python strftime formats <https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior/>`_
which explicitly specify the format, or the special string ``'iso-8601'``, which indicates that
`ISO 8601 <https://www.w3.org/TR/NOTE-datetime>`_ style times should be used. (eg ``'12:34:56.000000'``)

URLField
^^^^^^^^
*Supported by: Django ORM*

A :class:`RegexField` that validates the input against a URL matching pattern. Expects fully
qualified URLs of the form ``http://<host>/<path>``.

Corresponds to ``django.db.models.fields.URLField``. Uses Django's ``django.core.validators.URLValidator``
for validation.

**Signature**: ``URLField(max_length=200, min_length=None, allow_blank=False)``

UUIDField
^^^^^^^^^
*Supported by: Django ORM*

A field that ensures the input is a valid UUID string. The ``to_internal_value`` method will return
a ``uuid.UUID`` instance. On output the field will return a string in the canonical hyphenated
format, for example:

.. code-block:: python

    "de305d54-75b4-431b-adb2-eb6b9e546013"

**Signature**: ``UUIDField(format='hex_verbose')``

- ``format``: Determines the representation format of the uuid value
    - ``'hex_verbose'`` - The cannoncical hex representation, including hyphens: ``"5ce0e9a5-5ffa-654b-cee0-1238041fb31a"``.
    - ``'hex'`` - The compact hex representation of the UUID, not including hyphens: ``"5ce0e9a55ffa654bcee01238041fb31a"``.
    - ``'int'`` - A 128 bit integer representation of the UUID: ``"123456789012312313134124512351145145114"``.
    - ``'urn'`` - RFC 4122 URN representation of the UUID: ``"urn:uuid:5ce0e9a5-5ffa-654b-cee0-1238041fb31a"``.
      Changing the format parameters only affects representation values. All formats are accepted by
      ``to_internal_value``.