https://www.cnblogs.com/pyspark/p/8607801.html
https://www.cnblogs.com/LYliangying/articles/9896548.html
fieids.py主要定义了各种字段的序列化类。Field是基类。
class Field
_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)
子类
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)