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We'll set up a way to populate our database with Courses and Reviews and build the relationships between them.
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- Spring Data project
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Amazingly, with just
a few new Java classes,
0:00
we've produced a fully functional API.
0:03
But exploring it is a little
difficult without any data.
0:06
This is a common problem in
all sorts of development.
0:09
You wanna have a database populated with
test data so that you can kinda walk
0:12
through the workflow and
further walk through relationships.
0:15
We could very easily provide
some upload scripts that use SQL
0:19
to populate the database.
0:22
But that kinda messes up our rapid
application development flow that we've
0:23
been crafting, just by using entities.
0:26
Now what I mean by that is,
if we actually wrote SQL,
0:28
then whenever we change the entities, we
also need to fix our SQL scripts to match.
0:31
So what do we do?
0:35
Here comes some good news.
0:37
Spring Boot provides a simple way
to do this through the application
0:38
runner interface.
0:41
Here, let me show you and
0:43
then we'll use that data to setup
our course to review relationships.
0:44
Okay, so this is again one
of those pretty impressive.
0:48
It just works sort of things that
Spring Boot brings to the table.
0:52
Now don't blink because you might miss it.
0:55
Okay, so let's make a new
class that loads the database.
0:57
We can call it whatever, but
let's drop it in the core package, right?
1:00
Let's go in here to the core package and
we'll make a new class and
1:05
it's gonna load the database, so
what do you say we call it DatabaseLoader.
1:08
Could've been named whatever.
1:12
Okay, and now let's have it implement
1:14
the ApplicationRunner interface.
1:19
Okay, we've got some squiggles.
1:24
Let's go ahead and implement
the missing methods, which is just 1,
1:26
which is this run.
1:30
All right, now since we know
that we wanna create courses,
1:31
we need to get a handle
on the course repository.
1:36
So in order to get that,
we're going to use dependency injection.
1:39
That way we can get a handle on however
the repository is currently wired
1:43
up, okay?
1:46
So to do that first what
you do is you define
1:47
what it is you're trying
to get your hands on.
1:50
So we want private, let's set it final.
1:52
We don't need to change this and
1:54
we will say that we're looking for
the course repository.
1:55
And let's call it courses.
2:01
Okay, so we have that.
2:05
It's gonna say that it hasn't
been initialized which is good.
2:08
We're gonna add a constructor parameter
because again we're gonna mark this as
2:10
autowired and what that will do is
automatically wire up whatever we have
2:15
labeled as the course repository, nice.
2:20
And now we need to mark this
class as a component so
2:24
that it will be found on
component standard startup.
2:27
Let's make sure it knows what
we're talking about here.
2:36
Here we go.
2:39
And now we get access to a wired
up repository that will work with
2:40
all of our entities.
2:44
So let's use it.
2:45
So I'm going to create a course.
2:47
So I say Course course and
2:49
make sure you noticed I'm not
gonna make a new one of those.
2:52
And so again we setup a constructor
there that takes a title and a URL.
2:55
So let's go ahead and
let's do the original course Java basics.
2:59
Remember that and we will set
it to https://teamtreehouse.com,
3:04
that's /library/java-basics.
3:11
I am gonna go ahead and
3:16
get us some more real estate,
by closing all the tool windows.
3:17
Cool and now we can access
the repository that we imported, so
3:23
we'll say courses.save(course), okay.
3:27
And now our server is running, so
we've got to remember to restart it.
3:32
So, I'm gonna come down here and
I'm gonna click this restart button here.
3:35
Once this gets up and running if we flip
over, And we refresh our courses page.
3:40
We should see there it is, our course.
3:47
Let's go ahead and grab the first
course here, which is denoted
3:51
under the links tab itself, and
this is telling you what the page is.
3:54
Here, so let's go ahead and
grab this, grab courses/1.
3:58
Now 1 was the ID that was
automatically generated, and
4:02
you'll notice that it's not gonna
be in the properties for that.
4:06
We just have title and URL.
4:09
Spring data rest was smart enough and
hid the ID field from us.
4:11
Awesome, so now we have that course,
4:15
we know that reviews will work the same
way but it's time to make those related.
4:17
Remember, we have one course mini reviews,
and vice versa, right?
4:21
So let's model that.
4:25
Now I'm probably not gonna shock you
here but it's pretty easy to accomplish.
4:26
So if we go back to our course, And
4:30
we start by making,
let's make a new list, all right.
4:35
We will make a new private list of
reviews and we'll call it reviews.
4:37
Let's make sure that it knows
what we're talking about here.
4:46
Then we are going to
mark this as OneToMany.
4:54
And it's going to be mapped
by a field named course.
5:00
And the course field is going to be
on the reviews and it's not yet.
5:05
So we should just not gonna get
ahead of ourselves and go map that.
5:09
So let's go over to the review.
5:11
Well here, in this review,
I'm gonna move these guys up a bit.
5:13
And I will add the course field.
5:17
So here we have a private course and
it's called course.
5:24
And we want that to be ManyToOne
5:29
on the review, right?
5:34
Cool, so let's go ahead and
we can add the Getters and the Setters.
5:40
For that you can Getters and
Setters for the course.
5:43
Awesome, and let's flip back now
to the course and take a look.
5:48
And we wanna make sure that
whenever something is deleted,
5:53
like when this course gets deleted,
we wanna delete those reviews.
5:56
So we want the changes to do
what's known as cascading.
5:58
So we're gonna cascade.
6:01
And there's different types of cascading
but we're just gonna, really everything,
6:03
this is the pair here.
6:06
So CascadeType.ALL, and
that will do the proper wiring for us.
6:07
We also wanna make sure that
this new list gets initialized.
6:13
So here's an example of where we want to
add something in the generic constructor
6:17
and we wanna make this
reviews thing initialized.
6:22
Right, so we wanna say,
reviews = new ArrayList.
6:24
And we can use the diamond operator there.
6:27
And because course is calling this,
6:31
it's gonna automatically
initialize the reviews.
6:33
Nice, so let's do this,
let's generate a getter for the review.
6:37
So I'll definitely wanna make
sure that people can say,
6:42
hey what are the reviews related to this?
6:44
But what we don't want them to do is we
don't want them to set all of the reviews
6:46
because that would be pretty
easy to overwrite the review.
6:49
So a common practice is to allow
a new method that just adds.
6:51
Okay, so we're gonna say addReview.
6:56
So in here what we can do is we
can say review.setCourse(this) and
7:05
we'll set it to this and
reviews.add(review).
7:11
Now one thing that we
wanna do is make sure
7:15
that we have a constructor for reviews.
7:19
We had not created one of those earlier,
we just made the blank one.
7:23
So let's go ahead and do that.
7:26
The way that we're gonna
use it originally,
7:28
we're just gonna have
the rating in the description.
7:30
Let's keep the course off as just
being set the way that we did it.
7:33
If we wanna change this later, we can, we
can design this and it in a different way.
7:36
For now let's do it that way.
7:39
So back in our database loader.
7:42
Let's add a review.
7:43
And this is a review that I actually did
get on Java basics, if you remember to
7:45
make a little joke or I call myself a dork
in it and this is the review that I got.
7:50
It was a 3, not a 1, not bad but
it said this, you are a dork.
7:54
I think there are three
exclamation points.
8:02
Fair enough, true that.
8:04
Now if we come and restart the server.
8:07
When we refresh the courses here, you'll
see that there's now this review's link.
8:14
Cool, so courses/1/reviews, awesome.
8:19
So there's the reviews and it's linking
back and it's linking backwards as well
8:26
right so here's the course link and
it links back to review course.
8:29
Also, we can look at the review itself.
8:34
So if we go to the reviews/1.
8:36
You'll see that everything is linking
the way that it should, right.
8:38
So we can get to the course
from the review.
8:42
I wonder what happens if we
create a bunch of courses now.
8:46
One way to do that sort of
thing is to generate data.
8:50
Now I do this typically so I can
visualize what the API will look like.
8:52
Now it's not too hard but
please don't let it distract you.
8:56
But what this will do is it will help
our fellow teammates building out their
8:59
applications because now they're
gonna data to work with it.
9:02
So let's come over here and typically
what I do is I create the template.
9:05
That we're looking for, right?
9:10
So we're looking for a course title.
9:12
So it will make an array,
string, templates.
9:14
Let's see.
9:19
See what we can come up with here.
9:20
Hello up and running with %s and
9:22
how about we take a look into %s basics.
9:28
These are basically string templates.
9:37
How about %s for beginners.
9:41
How about %s for neckbeards.
9:44
About under the hood.
9:50
Something like that, right.
9:56
All those courses kind
of have the same names.
9:57
So little formatting trick there.
10:00
And then let's do this,
let's make some buzzwords all right,
10:05
some popular buzzwords.
10:08
Feel free to do whatever you want on here.
10:10
So do an array of buzzwords that
we might be having courses of,
10:11
let's do one specifically also.
10:17
Let's do Spring REST Data Java 9.
10:18
Scala, Scala, how are we gonna say that?
10:25
Groovy, let's do hibernate.
10:32
All right, now we could bring
in some random numbers but
10:41
let's just loop over these a little bit,
right?
10:43
So one way of doing this is using an int
stream which is introduced in Java 8.
10:45
It allows you to produce a stream
of integers between a range.
10:50
So it's like this.
10:53
So we're using, I'll say IntStream and
we will do a range from 0 to 100, okay.
10:55
And then we're gonna say forEach.
11:01
So for each one of those numbers,
we'll call it i just because
11:08
you usually do if we're doing a for
loop it would look kinda look like that.
11:12
And then we're gonna open
up our little lambda here.
11:14
And for each one of those what we wanna
do is we want to pull out a template.
11:17
And there's only a certain
amount of template.
11:22
So what we can do is we can use a module
load to get the next item in the list.
11:26
So we'll say i% which is
modulo templates.length.
11:30
And remember that will get us
the remainder and will for
11:34
sure be something that's
within the range of our list,
11:37
that's kind of a nice trick when you're
working through lists like number lists.
11:40
And then let's get a buzzword.
11:44
So this will say,
well this isn't a line and
11:44
say String_buzzword = buzzwords.
11:50
And we'll use the same
modular trick there.
11:57
% buzzwords.length.
12:00
Finally we'll put them together.
12:07
We'll say title =_String.format.
12:10
And we will give it the template that
we created and inject our buzzword.
12:12
And another title will be up and
running with spring this data sort of
12:20
thing and next we will make a course.
12:26
So let’s say course, c =,
because various course out there,
12:28
new course and going to pass and title and
whatever the URL is we could have
12:34
made this example.com,
great site for online learning.
12:39
If you now want to add the review so it's
a see dot Ad Review and we'll make a new
12:46
and here let's go ahead and
the ratings gonna be between one and five.
12:53
And we're going to format the message
that comes out here, let's say,
12:59
string format more please.
13:03
Basically, that's what most reviews are,
right?
13:09
We all want to learn more,
we can't get enough knowledge, so
13:11
we're going to say more buzz word, please.
13:14
Here we go.
13:19
And let's go ahead and let's,
outside of this little stream here,
13:20
let's add to an array list.
13:23
So let's say this is a list of courses.
13:27
I'll say this is a bunch of courses.
13:30
So new array list,
we'll try to avoid namespace inclusion,
13:33
I realize that these
variables are poorly named.
13:38
You can make a review and say that,
I did poorly name variables in this one.
13:43
So we're gonna say courses
which is are opposed and
13:49
we gonna say save and
we gonna pass in this bunch of courses.
13:54
Here we go so we have a bunch
of new courses and reviews.
13:58
So now whole bunch of stuff gets
generated including the original
14:02
that original courses is
still down here and move.
14:07
Let's move him up there with
14:11
radius from what I think
confused there we go.
14:16
All right now finally let's
restart the server and
14:21
make sure that our work was not all for
not come back over.
14:24
Start server up.
14:28
Awesome and if we come back and
we look at our courses page, our /courses.
14:34
What happened?
14:43
We forgot to add to the bunchOfCourses.
14:47
Probably sitting there screaming at me,
hit the add to the courses list.
14:50
So I'm gonna have courses and we're
gonna have that new course that we get
14:54
there we go and then restart the server.
14:58
You put that in the review to say like,
15:04
hey why don't you add that
to the course thing too.
15:05
All right, so we’re going to refresh.
15:10
Here we go, look at this.
15:13
Here's our Java nine basics,
scallop for beginners, groovy for
15:13
next periods under the hood with
Hibernate up and running with Springer.
15:18
That's a lot of data though, isn't it?
15:21
Can you imagine getting that
back from an API blast?
15:23
You know what, most websites they kind
of do kind of like a paging thing,
15:25
you know like eleven to twenty,
here's results twenty one to thirty.
15:29
That's paging, that's called paging.
15:31
Well guess what?
15:33
It comes for free.
15:34
So let's take a quick break,
15:35
and I'll introduce you how
to page in spring data rest.
15:36
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