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Filters are handy for displaying data on your web page in a dynamic way, without having to write special functions to control display.
More on Humanize: The Django documentation on the humanize set of filters.
Now that we have our CSS setup and
0:00
ready to go, let's see about making our
data more dynamic using template filters.
0:02
Remember that a filter is
applied to a variable that you
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pass into your template from your view,
and uses the pipe notation.
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Let's look at some of the filters
that Django includes for us.
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Open up coursedetail.html.
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So let's add a section at the top
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that lists out all of the steps
in this course in paragraph form.
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So, these are the steps in this course,
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c ourse.step_set.all.
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Let's start our server and
see what this looks like.
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So we changed directories into our
learning site, and then run the command,
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python manage.py runserver
on our favorite port.
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Now we can use the eye
to preview our page and
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we'll go into courses and select
Python Basics to be our test course.
1:02
And now we can see
the sentence that we added.
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But, this doesn't render very well,
does it?
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The new information that we added
is appearing in these brackets, and
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it's not very readable.
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We can use a join filter to break
up the items between these brackets
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without having to go into a for
loop or doing any other processing.
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So let's try that.
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Right here after all,
we add the pipe character, and
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then the word join because
we're using the join filter.
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And now we have to pass in the thing
that we want to separate our items by.
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And we do that by using a colon and
then opening some quotation marks.
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Whatever we want to use to separate these
items will go between the quotation marks.
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In this case since we're adding these
items to the end of a sentence,
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I want to separate each step
with a comma and a space.
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Now we close the quotation marks,
save the template, and
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we can refresh our page to
see what this looks like.
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Now this is much better.
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But if we use the length filter, we can
make this sentence even more useful.
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Using the length filter gives you
the number of items in a particular set.
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So let's see how that works.
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So instead of saying these
are the steps we can say
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there are a specific number of steps.
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And we can get at that number
by doing course.step_set.all
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using the pipe character again and
adding the length filter.
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The way the length filter works is this,
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even though we have this whole
expression course.step_set.all
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that uses our whole step set,
we won't see any of the data in that set.
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We won't see the titles that we see
later on in the sentence for example.
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Instead, the length filter just
gives us the length of the set, or
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in other words,
the number of items in the set.
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So if we save this template and reload our
page, we should see a number, and we do.
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There are two steps in this course.
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This works fine, but we should really be
using a built-in method called count.
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The length filter causes a large database
query to be run, so it saves our
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database some trouble if we use count
instead, because it's more efficient.
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So let's make that change.
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We can replace all type
length with just count.
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And whenever we refresh our page
we see that nothing has changed,
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everything is the same.
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We've just made our website more
efficient with this very simple change.
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Now, the parenthesis s parenthesis
that we have in the word steps isn't
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very readable.
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This is where another filter comes in.
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We can use the pluralize filter
to make the word step singular or
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plural based on the number
of steps in that set.
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So let's try this out.
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We just delete this entirely, and
replace it with course.step_set.count and
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then that pipe character and
the word pluralize.
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This one looks a little weird because you
have to type the word step as singular and
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then immediately follow it with
the set you're referring to in
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the pluralize filter.
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But basically, you're telling Django to
make this particular word, step, plural or
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singular based on the number of steps
in this set that you've attached to it.
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Again, the contents of the set won't
render and the number won't render.
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The only thing you'll see is an S
on the end of the word step or
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not, depending on how many
steps are in this course.
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Let's refresh the page, and
you can see what I mean.
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And there you have it.
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There are two steps plural in this course.
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There are also some other template tag
libraries that we can use in our projects.
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Let's test one out in the next video.
5:04
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