如何在Django模板中使用方法参数？

Question

我知道这里有一个帖子:django模板系统,在模型中调用一个函数来描述如何制作一个自定义模板过滤器来实现这一点,但从程序员的角度来看这是一个失败,因为这是一个不适合的东西那.你不能在Django的模板系统中调用带参数的方法似乎很荒谬.

Answer 1

作为哲学问题,Django团队决定不允许在视图中传递方法参数.就个人而言,我同意他们的意见; 它强制分离逻辑和演示文稿,我发现它很有帮助.它可以防止PHP因臭名昭着的意大利面条代码.

在链接的情况下,正确的做法是通过上下文将该调用的结果从视图传递到模板中.这样可以更加可维护.如果以后你需要更改my_related_deltas(3)到my_related_deltas(4),你去查看,这应该是相当精确的,而不是通过模板搜索搞清楚究竟在何处被定义.

Answer 2

尽管django作者建议不要用参数提供我们的方法,你仍然可以使用我写的这个"小"模板标签来做.

在我的例子中,我只是表明这是可能的.出于安全原因,我强烈建议您编写模板标签而不是尝试将参数传递给模型方法.

!警告!这仅用于测试目的!通过使用它你可能会入侵NASA以及你可能会被杀死.

class CallNode(template.Node):
    def __init__(self,object, method, args=None, kwargs=None, context_name=None):
        self.object = template.Variable(object)
        self.method = method
        if args:
            self.args = []
            for arg in args:
                self.args.append(template.Variable(arg))
        else:
            self.args = None

        if kwargs:
            self.kwargs = {}
            for key in kwargs:
                self.kwargs[key] = template.Variable(kwargs[key])
        else:
            self.kwargs = None

        self.context_name = context_name

    def render(self, context):
        object = self.object.resolve(context)
        if isinstance(object, str):
            raise template.TemplateSyntaxError('Given object is string ("%s") of length %d' 
                                               % (object, len(object)))

        args = []
        kwargs = {}
        if self.args:
            for arg in self.args:
                args.append(arg.resolve(context))
        if self.kwargs:
            for key in self.kwargs:
                kwargs[key] = self.kwargs[key].resolve(context)

        method = getattr(object, self.method, None)

        if method:
            if hasattr(method, '__call__'): 
                result = method(*args, **kwargs)
            else:
                result = method
            if self.context_name:
                context[self.context_name] = result
                return ''
            else:
                if not result == None: 
                    return result
                else:
                    return ''
        else:
            raise template.TemplateSyntaxError('Model %s doesn\'t have method "%s"' 
                                               % (object._meta.object_name, self.method))


@register.tag
def call(parser, token):
    """
    Passes given arguments to given method and returns result

    Syntax::

        {% call <object>[.<foreignobject>].<method or attribute> [with <*args> <**kwargs>] [as <context_name>] %}

    Example usage::

        {% call article.__unicode__ %}
        {% call article.get_absolute_url as article_url %}
        {% call article.is_visible with user %}
        {% call article.get_related with tag 5 as related_articles %}

        {% call object.foreign_object.test with other_object "some text" 123 article=article text="some text" number=123 as test %} 
    """

    bits = token.split_contents()
    syntax_message = ("%(tag_name)s expects a syntax of %(tag_name)s "
                       "<object>.<method or attribute> [with <*args> <**kwargs>] [as <context_name>]" %
                       dict(tag_name=bits[0]))

    temp = bits[1].split('.')
    method = temp[-1]
    object = '.'.join(temp[:-1])

    # Must have at least 2 bits in the tag
    if len(bits) > 2:
        try:
            as_pos = bits.index('as')
        except ValueError:
            as_pos = None
        try:
            with_pos = bits.index('with')
        except ValueError:
            with_pos = None

        if as_pos:
            context_name = bits[as_pos+1]
        else:
            context_name = None

        if with_pos:
            if as_pos:
                bargs = bits[with_pos+1:as_pos]
            else:
                bargs = bits[with_pos+1:]
        else:
            bargs = []

        args = []
        kwargs = {}

        if bargs:
            for barg in bargs:
                t = barg.split('=')
                if len(t) > 1:
                    kwargs[t[0]] = t[1]
                else:
                    args.append(t[0])

        return CallNode(object, method, args=args, kwargs=kwargs, context_name=context_name)
    elif len(bits) == 2:
        return CallNode(object, method)
    else:
        raise template.TemplateSyntaxError(syntax_message)