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Add a custom attribute to our model that we’ll then display in the list view of the admin site.
Resources:
Django Admin documentation on ModelAdmin.list_filter
Django Model documentation
Python documentation on the math module
If you've taken customizing Django
templates, you might remember writing
0:00
a custom filter that estimated how long it
would take someone to complete a course,
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based on how many words were
in the course description.
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It's not the most scientific method
of estimating time to completion, but
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that's fine.
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Now we're going to use the same
function we wrote in that course
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to add a custom attribute to our model
that will then display in the admin.
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Remember that custom template tags
are just regular Python functions, so
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we can import that function
into another module and use it.
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So, let's get started.
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Open up course_extras.py.
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So you see this function
here time_estimate?
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This is the function
we're going to be using.
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Now if you scroll to the top,
you'll see that we're all ready importing
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the course.models into course_extras,
which is great.
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We don't wanna change that.
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But it makes things a little tricky
when we import this function
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into our models.py file.
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Since we're going to be importing
time_estimate from coarse_extras.py into
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models.py., but since course_extras.py is
all ready importing one of the models,
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we would get an error if we added the
import statement to the top of models.py.
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Basically, we'd be trying to
do a recursive import and
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Python would be, what?
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So instead, let's go into the course
model and add our method,
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which we will call time_to_complete and
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then we'll add the import statement
directly inside this method.
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This will get us around any sort
of recursive import errors that we
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might encounter.
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So we define time_to_complete and
then we add the import statement.
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So, from
courses.templatetags.course_extras
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import time_estimate.
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We'll also want to return the result
of calling the time_estimate function,
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so we can go ahead and add that as well.
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Awesome.
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Now, remember that time estimate
is based on the number of words.
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So, we need to pass in
the number of words or
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the word count of the course description
into the time_estimate function call.
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Whenever we did this in
customizing Django templates,
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we got the word count using one
of Django's built-in filters.
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But in models.py,
we don't have access to that.
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Instead, we can get out the word
count using a combination
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of the built in Python functions len and
split.
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So, we'll just get the length
of self.description but
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that's just going to give us
the character count or the byte count.
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So instead, we add split and
then that will get us the word count.
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So save that, and
now all we need to do is add the time to
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complete attribute to the list
display in our CourseAdmin class.
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So, we go into admin.py and
right here in the CourseAdmin,
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inside the list display variable,
we just add time_to_complete.
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All right, save that and
then start your server,
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if it's not all ready started,
and refresh your courses list.
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And now you see that we have these
numbers underneath time to complete, and
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remember, these numbers stand in for
minutes.
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Now, one quick caveat.
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When I refreshed mine the first time,
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all I got was 0 minutes across the board
because our descriptions are so short.
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So, I went into a couple of courses, and
I replaced the course description with
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some sort of fun dessert-themed lorem
ipsum text just to bulk up the word
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count in the description and illustrate
how the time to complete would work.
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So feel free to Google,
like fun lorem ipsum and
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experiment with this for yourself.
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But as you can see, a number all by itself
like this this random 14 or this 25,
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is not super helpful.
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It's useful to have the unit of
measurement, like the minutes.
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And so we can add this to the method
on our model to return the minutes.
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So, we can return this
whole thing as a string.
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So, if we go back into models.py and we
add some things to this return statement.
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So we open up a string and
then we add these brackets and
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then min and close the string and
then we add format and
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we enclose the whole rest of this
line inside the format call.
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And we refresh our page.
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Then we have the minutes added so
we can see that Ruby Basics takes 14
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minutes versus Python testing,
which apparently takes no time at all.
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That looks a lot better.
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Great work.
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As you can see,
adding custom attributes to your list view
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is as easy as writing a little method to
bring back the information you need and
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then adding it to your admin class.
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Now, we've got this handy piece
of information at our fingertips.
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We could even use this to add
an extra filter to this page.
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Why don't you try that on your own?
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