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DIY, or Do It Yourself, custom template tags! Build a template tag that will provide you with a link to the newest course in our library at all times.
Django Documentation: Custom Template Tags and Filters
template is Django's module for all things template-related. We'll use this several times in the course.
template.Library is a class that lets us register new tags and filters through an instance of itself.
register.simple_tag(tag_name) or @register.simple_tag - Registers a function as a simple tag. Simple tags don't include new templates, don't have an end tag, and don't assign values to context variables.
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We've learned a lot about the built
in tools that Django ships with,
0:01
but sometimes you need
something even more custom.
0:05
Sometimes it's time to DIY
your own template tag.
0:09
Just like you can create templates
that you can include on the fly in
0:14
other templates,
you can also write template tags
0:18
that you can plug in to templates
that will render information.
0:22
For example, if you always wanted to
display the newest items added to a store
0:26
or the top-rated game, you can write
a custom tag that will dynamically
0:32
figure out what the newest or
best item is and display that for you.
0:37
That's exactly what we're
going to do in this video.
0:42
We're going to write a custom template
tag that will always display the newest
0:46
course available at the top of the page,
so people who come to our site frequently
0:51
can easily find courses they
might not have seen before.
0:56
So let's get started.
1:00
Template tags are a little special in that
they have to live in their own directory
1:03
called, templatetags.
1:07
So, we created a new directory in our
courses app, called templatetags.
1:09
Don't forget that in order for
Python to recognize template
1:14
tags as a Python package,
we had to add an empty init.py file.
1:18
So we created a new file and
saved it as __init__.py.
1:23
Then we created a second file in which we
will write our custom tags and filters.
1:29
We called that course_extras.py,
since these are the extra tags for
1:36
the course's app.
1:41
Now we're ready to get started.
1:42
Since this is a template tag, we need to
import the template module from Django.
1:44
That's because the template module
contains the function we need to register
1:51
our template.
1:55
When you register your template tag, what
you're doing is making it available to
1:57
Django's template language so
you can use it.
2:01
So let's go ahead and
create a variable called register,
2:04
that calls the class we'll need later,
and save ourselves some typing.
2:07
So register equals template.library.
2:11
This is basic Python code, but
let's review what we just did.
2:18
We instantiated an instance of the library
class located in the template library and
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named that instance register.
2:28
Okay, now we're ready to start
writing our template tag.
2:30
A template tag is just a function
that does a specific thing and
2:34
you can plug it into your template
using regular template syntax.
2:38
Like all functions,
it needs to be defined.
2:42
And then we can add a nice doc string
to let us know what this function does.
2:47
So it gets the most recent course
that was added to the library.
2:53
Now, we need to create our query.
2:59
We know we want to return the latest
course from the course model so
3:01
we can use a method called
latest to get at that like so.
3:06
We have to pass in the field in the model
that we want latest to pay attention to.
3:15
In this case,
we're concerned with the creation date, so
3:21
we used the created_at field
to get the latest course.
3:25
Now, do you see what I see?
3:29
We're using the course model,
but we haven't imported it yet.
3:31
So let's add that to our import statement.
3:34
From courses.models import Course.
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The last thing we need to
do is register our tag.
3:44
There are a few different kinds
of custom template tags, and
3:47
we'll go over those later.
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This one is a simple tag,
which returns its result as a string.
3:53
There are two different
ways to register your tag.
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There's the long way.
4:01
Register.simple_tag and then you feed in
4:03
the name of your tag, and that works fine,
we just add it right below our function.
4:08
But there's a shorter and
slightly cleaner way to do this.
4:13
We can use a decorator right
before our function and
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then we don't have to feed in anything.
4:24
Now in order for
our template tag to show up,
4:26
we have to let the template we're
dropping it into know that it exists.
4:29
Just like you have to use the extends tag
to say this template will extend that
4:33
other template, and you use the load tag
to say I want to load the static files.
4:38
You can also use the load tag, to load
your template tags into a template, and
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make them more accessible
to that template.
4:50
We want this tag to appear
in our layout.html template,
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so let's open that up.
4:56
We add the load tag to
the top of the page.
4:59
Load course_extras,
5:04
and now we can use our template
tag to get the most recent course.
5:07
So right here before the block content,
we add a p tag and it can say,
5:12
don't miss our latest course and
then we just drop in our tag.
5:16
Now let's start our server.
5:23
So we can change directories
into our learning site and
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then run python manage.py runserver.
5:31
And now here at the top we can see don't
miss our latest course, Python Testing.
5:39
You might be wondering why we created
this as a tag instead of just
5:45
getting this information in the view and
passing it in through the template.
5:50
And we could have done that.
5:54
But using the template tag for
this makes the code more reusable.
5:56
Once we've written that tag,
6:01
we don't have to perform
the work of calling the function,
6:03
returning the value, and adding
the template variable where we want it.
6:06
We just drop the tag in and
we're done, easy huh?
6:11
You can also create template tags that
take context, for example, that take
6:17
a string and use it to look something
up or that transform it in some way.
6:21
We'll get to that in a later video.
6:26
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