Django 模板标签可以像 Django 模板调用一样使用吗？

Question

I'm using the the Django Template Language to call into a model's method to create dynamic ids according to product-specific logic.

JSON files hold product-specific configuration information. I use the Django Template Language in strings in the JSON files so each product has their own logic for creating product-specific ids. It works great with a Django Template Language callables.

The id_template has a callable to the to a model's method get_next_policy_id:

{
    "model": "some name",
    "product_id": "some product name",
    "id_template": "{{ policy.get_next_product_id }}"
}

Here's the relevant code from the product model. You can see the method that provides the id, and the save method conditionally uses it.

class Policy():
    [...]
    def get_next_policy_id_risk_strategies(self):
        policy_num = -1
        sequence_name = self.product.product_id + '-' + self.source_application.form["state"]
        if self.source_application.form["state"] == "NY":
            policy_num = get_next_value(sequence_name, initial_value=200_000)

        elif self.source_application.form["state"] == "IA":
            policy_num = get_next_value(sequence_name, initial_value=400_000)
        else:
            sequence_name = self.product.product_id
            policy_num = get_next_value(sequence_name, initial_value=300_000)

        policy_id = self.product.product_id + "-" + str(policy_num)
        return policy_id

That works great. However, I'd like to have no product-specific code in the model. I could do this almost entirely in the Django Template Language, but the requirements for the product id, is they vary by state sequentially. So, get_next_value draws from a persisted sequence in the database. Thus, I'd like to move the conditional logic to the JSON file.

However, callables take no parameters. And I need to pass the start of the sequence and the state as parameters to generate the id. Since tags can take parameters, I thought to use simple tags, which can take parameters. Along with template language conditionals. I thought I should be able to have a template string like:

{
   "id_template": "{{ product.product_id }}-{% if product.source_application.form.state == \"NY\" %}{{ product.get_next_product_id "NY" 200000 }}{% elif product.source_application.form.state == \"IA\" %}{{ product.get_next_product_id "IA" 400000 }}{% else %}{{ product.get_next_product_id "other" 300000 }}{% endif %}"
}

Then, in the model, I'd place the following code:

    @register.simple_tag(name="get_next_product_id")
    def get_next_product_id(self, state, initial_value):
        sequence_name = self.product.product_id + "-" + self.source_application.form["state"]
        return get_next_value(sequence_name, initial_value=initial_value)

Unfortunately, I get an error from this:

E           django.template.exceptions.TemplateSyntaxError: Could not parse the remainder: ' "NY" 200000' from 'get_next_product_id "NY" 200000'

I thought simple tags could have arguments. Is that mistaken?

Because the template string is not being parsed, I simplified the string to the following:

{
   "id_template": "{{ product.get_next_product_id "NY" 200000 }}"
}

But the error remains the same. Removing the quotes around "NY" has no effect.

The question is:

Is what I am trying to do using Django Template Tags possible? And, if not, is there another way I should be moving the product-specific logic out of the model?

Answer 1

No that is not at all how it works. A template tag cannot be a method on a model. If you want to define a template tag, it needs to go in a file inside the templatetags directory of your app, and you need to call it with the tag syntax {%... %} . Of course because of that it can't accept self , you would need to pass the product explicitly.

So, in for example templatetags/my_tags.py:

@register.simple_tag(name="get_next_product_id")
def get_next_product_id(product, state, initial_value):
    sequence_name = product.product_id + "-" + product.source_application.form["state"]
    return get_next_value(sequence_name, initial_value=initial_value)

then in the template:

{% load my_tags %}
...
{% get_next_product_id product "NY" 200000 %}