- Building Our Model 7:46
- In Memory DAO implementation 1 question
- Template Reuse and Static Resources 11:04
- Template Reuse 1 question
- Adding to and Iterating a List 13:43
- Redirecting 1 objective
- Using Filters and Request Attributes 8:25
- Using filters 3 questions
- Accessing Specific Items 12:54
- Details 8:34
- URL Parameters 2 questions
- Messaging 6:10
- Build Your Own Flash Messages 14:13
- Review Messaging 3 questions
- Request Handled 1:39
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Accessing Specific Items
12:54Most web applications follow the same design pattern, there is a list of items and a more detailed view of each item. Let’s ensure you can access a specific item from your list by using what is known as a slug.
In just about every web
application you end up working on
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you're going to encounter
a couple of recurring patterns.
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Most notably you're going to show a list
of things just like we did with ideas, and
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then you're going to show each of those
items on a separate, more detailed page.
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Now, what this means is you'll need a way
to uniquely identify each of those items.
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Now, you've probably seen
some ugly URLs in your time,
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cruising around the interwebs.
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While we don't have one,
most web apps are using a database, and
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they usually provide a way to
uniquely identify an item,
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by what is known as an ID,
which is short for identifier.
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Well, those are usually numeric, and
some sites just pop them in their URL.
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But what does 231 mean to you?
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A better solution and best practice is to
use what is known as a slug whose origin
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isn't from that gross creature that hates
salt, but comes from the newspaper world.
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There's more info in the teacher's notes.
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Now since URLs can only
contain certain characters,
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you need to remove the unallowed ones,
yet still want things to be legible.
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Most search engines give heavy
weight to turns in the URL,
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meaning they will be more
likely to rise to the top.
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Also, for users who might want to share or
bookmark this,
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what makes more sense to you,
item number 231 or yoda-pez-dispensers?
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Which are you more likely to search for?
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In order for
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us to be able to vote on a specific idea,
we're going to need a way to identify it.
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Now, since we don't have a database, and
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this item doesn't have a unique
identifier, let's take the slug approach.
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Creating slugs is a part
of the Spark framework, but
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we can easily plugin an open source
library that will take care of it for us.
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Okay, so let's add our dependency.
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I searched for Java slug,
and I found slugify.
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The main independency information is here,
so let's grab this group ID
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and let's flip back over to our code,
and we'll go to Gradle file.
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Here we're gonna add, we're gonna say,
compile, add our dependency,
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calling it slugify, and
it's slugify, and it was 2.1.4.
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Okay, then we'll refresh
our Gradle dependencies.
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And now that we have that, let's head
over to our model so that we can use it.
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So our course ID, our model, is here.
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Go ahead and close the Gradle window,
create some more space.
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Okay, so what we want to do,
is in the constructor here,
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let's take what they pushed into
the title and just make a new slug.
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So we'll say Slugify
slugify equals new Slugify.
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Now this Slugify throws
an unhandled exception.
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It throws an I/O exception,
we're probably not gonna run into that.
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And let's not worry about being
too defensive about this.
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We'll just write something out to
the screen with this printStackTrace.
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Not really the best practice.
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We probably want to do
something deeper than that,
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but we're just working
through this right now.
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So we'll do slugify.slugify.
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Here we're gonna pass on the title there,
and we're gonna store that slug.
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And we'll store that in a new field,
right, this new field here.
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We'll make a new create field slug.
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We'll make it a string called slug.
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And.
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SInce we have a slug here,
we'll add a new getter for it, right?
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So we'll generate a new getter.
Since the title is not updatable,
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right, we can't set the title,
only getters are here.
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We don't need to worry about the slug and
the title getting out of sync.
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If we added one, we'd have to
make sure that that had it, but
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we don't have that right now.
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So let's not worry about that, all right?
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And we wanna be able to find
one of these course ideas,
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by this new slug that we just added,
right?
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So let's pop over to the interface,
our CourseIdeaDAO here,
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and we're going to add
the ability to find one by slug.
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So we'll say findBySlug.
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And then what will happen is
the user will pass in a slug.
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And if we go to our simple
don't do this at home model
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we can have it implement that new method,
which now it's complaining about.
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All right, it's complaining
that it doesn't implement, so
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select implement methods findBySlug.
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Okay, this is an excellent place
to show off the power of streams.
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If you haven't seen these before,
this might blow your mind, but
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I just want to show you
here how powerful this is.
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Now we know that we're using Java 8,
cuz of all the lambdas and
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everything that we've seen so far.
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So one of the really powerful things
in Java 8 is this idea of streams.
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And what happens is, you kinda chain.
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So for each one of the ideas,
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what we'll do is we'll pick out
everything that doesn't match.
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We'll only keep ones
that do match this slug.
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So we'll say filter (idea
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-> idea.getSlug().equals(slug))
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Cool.
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And whichever the first one is that
we find, there's what we want.
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So there's actually
a method called findFirst.
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So it's gonna go through that filter.
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The first one that matches
is what's gonna come here.
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Now if it doesn't find one,
what happens is,
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what's returned is what's
known as an optional.
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And an optional is a way of
protecting against nulls.
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So they offer a great form of protection.
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Now what we want to return is
we want to return a CourseIdea.
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So if we do orElseThrow, this is what
we're gonna do if we didn't find one,
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we want an exception to happen, okay?
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So we're gonna say NotFoundException.
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This is a new class that we're
gonna make here in a second.
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And this is a method reference,
if you remember from the workshop.
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So this will throw this NotFoundException.
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And we'll say here,
we'll say Create Class NotFoundException.
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And we want it in the model package.
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And we'll gonna just go ahead and say
that this extends a RunTimeException,
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right, because we don't know until
runtime that this is a bug.
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Okay, awesome, so
we will try to find the slug.
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And if it doesn't happen,
we're gonna throw this NotFoundException.
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It's pretty succinct, right?
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So we're going to stream,
we're going to look at each idea.
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And if the idea, if its slug equals
the slug that we're looking for,
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we're going to get it back, or
else we're going to throw a new exception.
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So we could've written that
in the imperative way,
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but I wanted to show off
streams a little bit here.
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Okay, so where were we,
sorry I got distracted, nerd-sniped.
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All right, so
let's add a way to store our voters.
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Since you're only allowed to vote once
per idea, let's use a set of user names.
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That'll take care of the problem
by ensuring uniqueness, right?
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So, let's flip back to our
CourseIdea model here.
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And we're going to add a new sets of
strings, so it's a set of user names,
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of strings that are,
we'll call voters, sorry.
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And it is definitely Java Set, and
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we need to initialize
that when it comes in.
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So, we'll say voters = new HashSet.
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All right, so.
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Let's add a convenience method
that will allow us to add a voter.
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So we'll say public, and when we add it,
we want to let them know whether or
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not it was added successfully.
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So we'll say voterUserName, and
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we'll just return voters dot add,
which is voterUserName.
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Cool, that makes sense?
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Sets, when you call add on Sets,
it will return a true or false.
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So, that's what we want.
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And let's do a count of how
many times it's been voted for.
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So let's say, public int getVoteCount.
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That's probably some data that
we'll want to show, right?
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How popular is this?
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Okay, now let's add a handler
that will track the vote.
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So we want to put the dynamic
slug right into the URL.
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So how do we define that path?
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Let's go to Main here.
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So we know that we want it to be a post,
right, because they're posting a new vote.
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So it's ideas.
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And how do we add the slug?
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Well, the good news is,
it's super straight forward.
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All you need to do is put a colon
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followed by the name of the parameter
that you'd like to refer to later.
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So we're gonna say slug/vote.
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And then, of course,
we're gonna take a request and response.
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We're gonna open up that route.
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Okay, and in here,
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what we wanna do is, let's go find
a CourseIdea, should it exist.
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We'll do dao.
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our new method, findBySlug().
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And we're going to pull that
parameter off of the request, and
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that is just like you might
think on a thing called params.
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So that's pulling whatever was in the URL
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at this place in between these
two slashes, slug and slug here.
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Nice, right?
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So now let's add the user as a voter.
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So we're gonna do idea.addVoter, and
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we're gonna do req.attribute.
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Remember we're using
the attributes username.
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Okay, we've now added the voter.
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And let's pop them back
to the idea list so
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that they can see the vote count pop up.
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Okay, that looks like a good design there,
so
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they'll vote and we'll add a voter
to the CourseIdea, should it exist.
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Okay, so now what we need to do is
we need to modify that template so
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that we have a place to
send those requests.
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So let's go to our ideas template.
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Okay, so let's,
inside each one of these list items,
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why don't we make each one
of these a form, okay?
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So I'm gonna come in and
I'm gonna add a new form, and
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that's gonna go to our new page.
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So we're gonna say ideas.
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And remember,
we added that getter for get slug.
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And it's gonna make a vote.
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And that was a method of post.
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Okay, let's move this
title up inside the form.
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So each list item is gonna have a form.
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That form is gonna show the title,
and then let's show the vote count.
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Remember, we created that method
called getVoteCount, but
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it's called voteCount
here in this section, and
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we need to give everybody
a button that says Vote.
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Okay, so let's reboot that server and
let's go add a few.
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So I'm going to view all course ideas.
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Let's add Spark Testing.
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And let's add the Ninja Framework.
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All right, so let's vote.
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Okay, so I'm gonna vote for
this Spark Test thing.
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Boom.
Awesome.
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It's up to 1.
Now what if I do it again?
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Nothing.
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Hm.
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That's right.
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We made it a set so there can only be one.
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We really should be showing
them an error message.
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Hm.
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Let's make sure that this was working for
different users as well.
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So I'm gonna erase my cookie,
I'm gonna refresh this page, and
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it should have us go back to login.
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Let's log in as the thought leader,
chalkers.
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Let's go and view all course ideas,
and let's have him vote here.
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Great, there's two votes.
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You know what would be cool?
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What if we add a detail page that was just
for this one idea, right, like you click
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this and it went to a detail page, and
it listed all the voters who voted on it?
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That's actually a great way for
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you to recall a lot of what you've
learned through this course.
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Why don't you take that on?
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In the next video,
I'll show you how I did it, but
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why don't you give it a spin first?
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I've put some directions
in the teacher's notes.
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Have fun, you got this.
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