DRF源码-fields.py

    _creation_counter = 0

    default_error_messages = {
        ‘required‘: _(‘This field is required.‘),
        ‘null‘: _(‘This field may not be null.‘)
    }
    default_validators = []     #默认验证器初始化为空list
    default_empty_html = empty
    initial = None

    # 在构造函数中，给出了各种定义参数，由子类继承，在实例化时传参，来控制这个字段的各种属性
    # read_only，表明只用于序列化输出
    # write_only， 表明只用于反序列化输入，比如密码
    # required， 表明在反序列化时必须输入
    # default， 反序列化时使用的默认值
    # initial
    # source，
    # label， 用于HTML展示API页面时，显示的字段名称
    # help_text， 用于HTML展示API页面时，显示的字段帮助提示信息
    # style
    # error_messages， 包含错误编号与错误信息的字典
    # validators， 该字段使用的验证器
    # allow_null, 表明该字段是否允许传入None，默认False
    def __init__(self, read_only=False, write_only=False,
                 required=None, default=empty, initial=empty, source=None,
                 label=None, help_text=None, style=None,
                 error_messages=None, validators=None, allow_null=False):
        self._creation_counter = Field._creation_counter
        Field._creation_counter += 1

        # If `required` is unset, then use `True` unless a default is provided.
        if required is None:
            required = default is empty and not read_only

        # Some combinations of keyword arguments do not make sense.
        # 断言一些没有意义的参数组合
        assert not (read_only and write_only), NOT_READ_ONLY_WRITE_ONLY
        assert not (read_only and required), NOT_READ_ONLY_REQUIRED
        assert not (required and default is not empty), NOT_REQUIRED_DEFAULT
        assert not (read_only and self.__class__ == Field), USE_READONLYFIELD

        # 将传入的参数赋值给实例（属性初始化）
        self.read_only = read_only
        self.write_only = write_only
        self.required = required
        self.default = default
        self.source = source
        self.initial = self.initial if (initial is empty) else initial
        self.label = label
        self.help_text = help_text
        self.style = {} if style is None else style
        self.allow_null = allow_null

        if self.default_empty_html is not empty:
            if default is not empty:
                self.default_empty_html = default

        if validators is not None:
            self.validators = list(validators)

        # These are set up by `.bind()` when the field is added to a serializer.
        self.field_name = None
        self.parent = None

        # Collect default error message from self and parent classes
        messages = {}
        for cls in reversed(self.__class__.__mro__):
            messages.update(getattr(cls, ‘default_error_messages‘, {}))
        messages.update(error_messages or {})
        self.error_messages = messages

    # .validators is a lazily loaded property, that gets its default
    # value from `get_validators`.
    # validators属性设置
    @property
    def validators(self):
        if not hasattr(self, ‘_validators‘):
            self._validators = self.get_validators()
        return self._validators

    @validators.setter
    def validators(self, validators):
        self._validators = validators

    def get_validators(self):
        return list(self.default_validators)

class IntegerField(Field):
    default_error_messages = {
        ‘invalid‘: _(‘A valid integer is required.‘),
        ‘max_value‘: _(‘Ensure this value is less than or equal to {max_value}.‘),
        ‘min_value‘: _(‘Ensure this value is greater than or equal to {min_value}.‘),
        ‘max_string_length‘: _(‘String value too large.‘)
    }
    MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
    re_decimal = re.compile(r‘\.0*\s*$‘)  # allow e.g. ‘1.0‘ as an int, but not ‘1.2‘

    def __init__(self, **kwargs):
        # 从变长传参里找max_value，min_value，给到实例，默认为None
        #继承父类的其他属性（相当于父类属性是通用，这里的属性是子类独有的）
        self.max_value = kwargs.pop(‘max_value‘, None)
        self.min_value = kwargs.pop(‘min_value‘, None)
        super().__init__(**kwargs)
        # 如果传参max_value，先拼接error message，然后在validators属性里添加一个验证器元素。
        if self.max_value is not None:
            message = lazy_format(self.error_messages[‘max_value‘], max_value=self.max_value)
            self.validators.append(
                MaxValueValidator(self.max_value, message=message))
        if self.min_value is not None:
            message = lazy_format(self.error_messages[‘min_value‘], min_value=self.min_value)
            self.validators.append(
                MinValueValidator(self.min_value, message=message))

    def to_internal_value(self, data):
        if isinstance(data, str) and len(data) > self.MAX_STRING_LENGTH:
            self.fail(‘max_string_length‘)

        try:
            data = int(self.re_decimal.sub(‘‘, str(data)))
        except (ValueError, TypeError):
            self.fail(‘invalid‘)
        return data

    def to_representation(self, value):
        return int(value)

class CharField(Field):
    default_error_messages = {
        ‘invalid‘: _(‘Not a valid string.‘),
        ‘blank‘: _(‘This field may not be blank.‘),
        ‘max_length‘: _(‘Ensure this field has no more than {max_length} characters.‘),
        ‘min_length‘: _(‘Ensure this field has at least {min_length} characters.‘),
    }
    initial = ‘‘

    def __init__(self, **kwargs):
        self.allow_blank = kwargs.pop(‘allow_blank‘, False)
        self.trim_whitespace = kwargs.pop(‘trim_whitespace‘, True)
        self.max_length = kwargs.pop(‘max_length‘, None)
        self.min_length = kwargs.pop(‘min_length‘, None)
        super().__init__(**kwargs)
        if self.max_length is not None:
            message = lazy_format(self.error_messages[‘max_length‘], max_length=self.max_length)
            self.validators.append(
                MaxLengthValidator(self.max_length, message=message))
        if self.min_length is not None:
            message = lazy_format(self.error_messages[‘min_length‘], min_length=self.min_length)
            self.validators.append(
                MinLengthValidator(self.min_length, message=message))

        # ProhibitNullCharactersValidator is None on Django < 2.0
        if ProhibitNullCharactersValidator is not None:
            self.validators.append(ProhibitNullCharactersValidator())

    def run_validation(self, data=empty):
        # Test for the empty string here so that it does not get validated,
        # and so that subclasses do not need to handle it explicitly
        # inside the `to_internal_value()` method.
        if data == ‘‘ or (self.trim_whitespace and str(data).strip() == ‘‘):
            if not self.allow_blank:
                self.fail(‘blank‘)
            return ‘‘
        return super().run_validation(data)

    # 将int，float转为为str
    def to_internal_value(self, data):
        # We‘re lenient with allowing basic numerics to be coerced into strings,
        # but other types should fail. Eg. unclear if booleans should represent as `true` or `True`,
        # and composites such as lists are likely user error.
        if isinstance(data, bool) or not isinstance(data, (str, int, float,)):
            self.fail(‘invalid‘)
        value = str(data)
        return value.strip() if self.trim_whitespace else value

    def to_representation(self, value):
        return str(value)