Supported Types¶
The following view function signature expects two additional parameters in the url: hrs and mins. DMP converts these to int automatically.
@view_function
def process_request(request, hrs:int=12, mins:int=30):
...
In the above function, hrs and mins are set to the following integers:
/homepage/index/111/222/ |
hrs=111; mins=222 |
/homepage/index/111/222 |
hrs=111; mins=222 |
/homepage/index/-/222 |
hrs=12 (default); mins=222 |
/homepage/index//222 |
hrs=12 (default); mins=222 |
/homepage/index/111 |
hrs=111; mins=30 (default) |
Built-in Types¶
Out of the box, DMP converts the following types:
| Type Hint: | Conversion: | Empty (default used) when value is: |
|---|---|---|
str |
No conversion | '' |
int |
int(value) |
'', - |
float |
float(value) |
'', - |
decimal.Decimal |
decimal.Decimal(value) |
'', - |
bool |
value[0] not in ( 'f', 'F', '0', False ) |
'', - (see notes below) |
datetime.datetime |
First matching format in settings.DATETIME_INPUT_FORMATS |
'', - |
datetime.date |
First matching format in settings.DATE_INPUT_FORMATS |
'', - |
Model subclass |
YourModel.objects.get(id=value) |
'', -, 0 (see notes below) |
object |
The fallback, no conversion | '' |
Boolean Values¶
Consider the following signature:
@view_function
def process_request(request, forward:bool=True):
...
In the signature, forward has a type hint and a default value, making it optional in the URL. Consider how forward is evaluated in the following URLs:
http://localhost:8000/homepage/index/6/30 |
Evaluates True because the third parameter is missing. It is assigned the default value of True (per the function signature). |
http://localhost:8000/homepage/index/6/30/0/ |
Evaluates False because the third parameter is 0. |
http://localhost:8000/homepage/index/6/30/0/ |
Evaluates False because the third parameter is f. |
http://localhost:8000/homepage/index/6/30/AA/ |
Evaluates True because the third parameter is AA
(not one of the False characters). |
http://localhost:8000/homepage/index/6/30/-/ |
Evaluates True because the third parameter is a dash -, and DMP assigns
the parameter default (forward:bool=True). |
http://localhost:8000/homepage/index/6/30/%20/ |
Evaluates True because the third parameter is a space, and DMP assigns
the parameter default (forward:bool=True). |
While these conversion characters may seem a little arbitrary, these characters allow you to create “pretty” urls, with a dash denoting “empty”.
Django Models¶
URL parameters are excellent places to specify ids of model objects. For example, suppose the id for Purchase object #1501 is coded in a receipt page URL: http://localhost:8000/storefront/receipt/1501/. The following view function signature would automatically get the object from your database:
from django_mako_plus import view_function
from storefront.models import Purchase
@view_function
def process_request(request, purchase:Purchase):
# the `purchase` variable has already been pulled from the database
In the above URL, one of two outcomes will occur:
- If a Purchase record with primary key 1501 exists in the database, it is sent into the function.
- If it doesn’t exist, DMP raises Http404.
But in the slightly different URL, http://localhost:8000/storefront/receipt/-/, a third option happens. The view function is called, even though “dash” isn’t a valid object ID. Since the dash means “empty”, the purchase parameter will be None. In fact, when converting Model parameters, the empty string, the dash, and a zero all cause the object to be None.
The purpose of the “empty” values, which calls the function with purchase => None, allows your application to create URLs with objects explictily set to None.
Specifying Model Types¶
Since Python usually parses converter functions before your models are ready, you can’t reference them by type. This issue is described in the Django documentation.
In other words, the following doesn’t work:
from django_mako_plus import parameter_converter
from homepage.models import Question
@parameter_converter(Question)
def convert_question(value, parameter):
...
DMP uses the same solution as Django when referencing models: use “app.Model” syntax. In the following function, we specify the type as a string. After Django starts up, DMP replaces the string with the actual type.
from django_mako_plus import parameter_converter
@parameter_converter("homepage.Question")
def convert_question(value, parameter):
...
Using string-based types only works with models (not with other types).