Handy Dandy 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 0:08 pass into your template from your view, and uses the pipe notation. 0:11 Let's look at some of the filters that Django includes for us. 0:16 Open up coursedetail.html. 0:21 So let's add a section at the top 0:23 that lists out all of the steps in this course in paragraph form. 0:27 So, these are the steps in this course, 0:31 c ourse.step_set.all. 0:38 Let's start our server and see what this looks like. 0:44 So we changed directories into our learning site, and then run the command, 0:48 python manage.py runserver on our favorite port. 0:52 Now we can use the eye to preview our page and 0:59 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. 1:07 But, this doesn't render very well, does it? 1:09 The new information that we added is appearing in these brackets, and 1:12 it's not very readable. 1:15 We can use a join filter to break up the items between these brackets 1:18 without having to go into a for loop or doing any other processing. 1:22 So let's try that. 1:26 Right here after all, we add the pipe character, and 1:28 then the word join because we're using the join filter. 1:32 And now we have to pass in the thing that we want to separate our items by. 1:36 And we do that by using a colon and then opening some quotation marks. 1:41 Whatever we want to use to separate these items will go between the quotation marks. 1:46 In this case since we're adding these items to the end of a sentence, 1:50 I want to separate each step with a comma and a space. 1:55 Now we close the quotation marks, save the template, and 1:59 we can refresh our page to see what this looks like. 2:03 Now this is much better. 2:07 But if we use the length filter, we can make this sentence even more useful. 2:09 Using the length filter gives you the number of items in a particular set. 2:14 So let's see how that works. 2:18 So instead of saying these are the steps we can say 2:20 there are a specific number of steps. 2:24 And we can get at that number by doing course.step_set.all 2:27 using the pipe character again and adding the length filter. 2:34 The way the length filter works is this, 2:38 even though we have this whole expression course.step_set.all 2:42 that uses our whole step set, we won't see any of the data in that set. 2:47 We won't see the titles that we see later on in the sentence for example. 2:52 Instead, the length filter just gives us the length of the set, or 2:56 in other words, the number of items in the set. 3:01 So if we save this template and reload our page, we should see a number, and we do. 3:04 There are two steps in this course. 3:10 This works fine, but we should really be using a built-in method called count. 3:12 The length filter causes a large database query to be run, so it saves our 3:18 database some trouble if we use count instead, because it's more efficient. 3:22 So let's make that change. 3:27 We can replace all type length with just count. 3:29 And whenever we refresh our page we see that nothing has changed, 3:35 everything is the same. 3:39 We've just made our website more efficient with this very simple change. 3:40 Now, the parenthesis s parenthesis that we have in the word steps isn't 3:44 very readable. 3:49 This is where another filter comes in. 3:51 We can use the pluralize filter to make the word step singular or 3:53 plural based on the number of steps in that set. 3:58 So let's try this out. 4:02 We just delete this entirely, and replace it with course.step_set.count and 4:03 then that pipe character and the word pluralize. 4:10 This one looks a little weird because you have to type the word step as singular and 4:14 then immediately follow it with the set you're referring to in 4:20 the pluralize filter. 4:24 But basically, you're telling Django to make this particular word, step, plural or 4:27 singular based on the number of steps in this set that you've attached to it. 4:32 Again, the contents of the set won't render and the number won't render. 4:37 The only thing you'll see is an S on the end of the word step or 4:43 not, depending on how many steps are in this course. 4:47 Let's refresh the page, and you can see what I mean. 4:51 And there you have it. 4:55 There are two steps plural in this course. 4:56 There are also some other template tag libraries that we can use in our projects. 4:59 Let's test one out in the next video. 5:04