一、Form基础
（一）Form的作用
Django的Form主要有以下几大作用：
- 生成HTML标签
- 验证用户数据（显示错误信息）
- Form提交保留上次提交数据
- 初始化页面显示数据
（二）实例
一般网站都有登录页面，如果使用Form应该怎么做呢？
1、创建LoginForm类
from django import forms class LoginForm(forms.Form): username = forms.CharField(max_length=32) password = forms.CharField(max_length=32)
2、views中进行实例化
def login(request): if request.method == 'GET': #实例化LoginForm form = LoginForm() #发送的是POST请求 form = LoginForm(data=request.POST) #对数据进行验证 if form.is_valid(): print(form.cleaned_data) return redirect('/index/') return render(request,'login.html',{'form':form})
3、login.html中使用
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> </head> <body> <form method="post" action="/login/"> {% csrf_token %} {{ form }} <!--自动生成html标签--> <input type="submit"/> </form>
这样很容易就完成了登录功能，并且Form的作用也都体现出来了。
（三）forms字段和插件
在上述实例中，使用Form需要创建一个Form相关的类，并且在类中写入相关的forms字段，这里涉及到Field类，是所有forms字段最根本的基类，它位于django.forms.Field下：
class Field: widget = TextInput # Default widget to use when rendering this type of Field. hidden_widget = HiddenInput # Default widget to use when rendering this as "hidden". default_validators = [] # Default set of validators # Add an 'invalid' entry to default_error_message if you want a specific # field error message not raised by the field validators. default_error_messages = { 'required': _('This field is required.'), } empty_values = list(validators.EMPTY_VALUES) def __init__(self, *, required=True, widget=None, label=None, initial=None, help_text='', error_messages=None, show_hidden_initial=False, validators=(), localize=False, disabled=False, label_suffix=None): # required -- Boolean that specifies whether the field is required. # True by default. # widget -- A Widget class, or instance of a Widget class, that should # be used for this Field when displaying it. Each Field has a # default Widget that it'll use if you don't specify this. In # most cases, the default widget is TextInput. # label -- A verbose name for this field, for use in displaying this # field in a form. By default, Django will use a "pretty" # version of the form field name, if the Field is part of a # Form. # initial -- A value to use in this Field's initial display. This value # is *not* used as a fallback if data isn't given. # help_text -- An optional string to use as "help text" for this Field. # error_messages -- An optional dictionary to override the default # messages that the field will raise. # show_hidden_initial -- Boolean that specifies if it is needed to render a # hidden widget with initial value after widget. # validators -- List of additional validators to use # localize -- Boolean that specifies if the field should be localized. # disabled -- Boolean that specifies whether the field is disabled, that # is its widget is shown in the form but not editable. # label_suffix -- Suffix to be added to the label. Overrides # form's label_suffix. self.required, self.label, self.initial = required, label, initial self.show_hidden_initial = show_hidden_initial self.help_text = help_text self.disabled = disabled self.label_suffix = label_suffix widget = widget or self.widget if isinstance(widget, type): widget = widget() else: widget = copy.deepcopy(widget) # Trigger the localization machinery if needed. self.localize = localize if self.localize: widget.is_localized = True # Let the widget know whether it should display as required. widget.is_required = self.required # Hook into self.widget_attrs() for any Field-specific HTML attributes. extra_attrs = self.widget_attrs(widget) if extra_attrs: widget.attrs.update(extra_attrs) self.widget = widget messages = {} for c in reversed(self.__class__.__mro__): messages.update(getattr(c, 'default_error_messages', {})) messages.update(error_messages or {}) self.error_messages = messages self.validators = list(itertools.chain(self.default_validators, validators)) super().__init__() def prepare_value(self, value): return value def to_python(self, value): return value def validate(self, value): if value in self.empty_values and self.required: raise ValidationError(self.error_messages['required'], code='required') def run_validators(self, value): if value in self.empty_values: return errors = [] for v in self.validators: try: v(value) except ValidationError as e: if hasattr(e, 'code') and e.code in self.error_messages: e.message = self.error_messages[e.code] errors.extend(e.error_list) if errors: raise ValidationError(errors) def clean(self, value): """ Validate the given value and return its "cleaned" value as an appropriate Python object. Raise ValidationError for any errors. """ value = self.to_python(value) self.validate(value) self.run_validators(value) return value def bound_data(self, data, initial): """ Return the value that should be shown for this field on render of a bound form, given the submitted POST data for the field and the initial data, if any. For most fields, this will simply be data; FileFields need to handle it a bit differently. """ if self.disabled: return initial return data def widget_attrs(self, widget): """ Given a Widget instance (*not* a Widget class), return a dictionary of any HTML attributes that should be added to the Widget, based on this Field. """ return {} def has_changed(self, initial, data): """Return True if data differs from initial.""" # Always return False if the field is disabled since self.bound_data # always uses the initial value in this case. if self.disabled: return False try: data = self.to_python(data) if hasattr(self, '_coerce'): return self._coerce(data) != self._coerce(initial) except ValidationError: return True # For purposes of seeing whether something has changed, None is # the same as an empty string, if the data or initial value we get # is None, replace it with ''. initial_value = initial if initial is not None else '' data_value = data if data is not None else '' return initial_value != data_value def get_bound_field(self, form, field_name): """ Return a BoundField instance that will be used when accessing the form field in a template. """ return BoundField(form, self, field_name) def __deepcopy__(self, memo): result = copy.copy(self) memo[id(self)] = result result.widget = copy.deepcopy(self.widget, memo) result.validators = self.validators[:] return result