Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
We often need to do things at the beginning of a request or at the end of one, before the response is sent back. In our case now, we need to connect to the database on the way in, and disconnect from it on the way out. Luckily, Flask provides two handy decorators for this.
New Terms
-
g- A global object that Flask uses for passing information between views and modules. -
before_request- A decorator to mark a function as running before the request hits a view. -
after_request- A decorator to mark a function as running before the response is returned.
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
[MUSIC]
0:00
In this video, we're going to set up the
database of our Flask app.
0:04
As part of that, we need to handle
connecting to and
0:08
disconnecting from our database
responsibly.
0:10
Flask gives us two really useful
decorators that we can
0:13
use to make code happen as a request is
coming in and as the request is going out.
0:16
Flask also gives us the super handy G
object,
0:21
which lets us make different things
global.
0:23
We'll use it to make our database
connection and
0:26
our current user available everywhere.
0:28
Alright.
So,
0:31
if we're gonna do this, we need to create
our Flask app.
0:31
So, let's make a new file here.
0:36
Let's call this we'll call it app.py.
0:38
So we're gonna need to import a few
things.
0:41
So let's say from flask import Flask, and
I know I'm going to need g,
0:44
which we'll get to in a minute, it's this
global thing.
0:49
And then we're gonna need models.
0:53
And since we're gonna have more models
later on,
0:55
cuz we have to do the whole social thing
and posts and all that.
0:57
I'm just gonna import models, as a whole,
1:00
instead of doing like, from models import
user.
1:02
Okay.
Let's set a couple of things up here.
1:05
So, we'll set DEBUG = True, we'll set PORT
1:08
= 8000 and we'll set HOST = all zeros.
1:13
If you did the previous Flask course we
just always specified this
1:17
in the app.run down at the bottom.
1:20
I think it's a little bit cleaner to do
these as variables.
1:22
And then we just change them in one spot.
1:25
Or if you start deploying to things like
Heroku and
1:26
you're gonna use the environment
variables.
1:30
Now, you can just set them up here instead
of having to
1:32
kinda wiggle them around and move them.
1:35
Let's create our app.
1:37
Which remember we do Flask(__name__) and
1:39
then the two methods that we need to
create
1:41
the one that runs before the request and
the one that runs after the request.
1:45
Let's go ahead and create those.
1:49
So, we're gonna decorate them with
@app.before_request and
1:52
then we're gonna name it,
1:56
I'm just gonna name it before_request cuz
it really doesn't matter.
1:58
And so to describe what we're gonna do
here,
2:03
we're gonna Connect to the database before
each request.
2:06
Okay, easy enough.
2:11
And now we're gonna use g.
2:11
G is this global object.
2:14
It gets passed around all the time inside
Flasks, so
2:15
we can use this to like, set up things
that we want to have available everywhere.
2:18
Which is, exactly what we're going to do.
2:22
So [LAUGH], g.db is going to be
=models.database.
2:25
That way it's just easier, we can always
use g.db for doing stuff.
2:30
And we're gonna make sure to call
g.db.connect
2:35
beginning of every single request.
2:39
Okay.
2:41
Our second one is @app.after_request.
2:41
Very creatively named.
2:48
[BLANK_AUDIO]
2:49
And so we're gonna call this one
after_request as well.
2:51
And this one actually takes the response
object.
2:55
So, you know, we do like return render
template or
2:58
return redirect or whatever, that return
there is the response.
3:01
That actually gets passed into this
function, so
3:06
we're gonna describe this one too.
3:09
We'll say Close the database connection
after each request,
3:10
just to make sure we know what's going on.
3:17
And we'll call it g.db.close.
3:19
And then we want to return the response.
3:23
And then if we want to, down at the
bottom, let's give this,
3:26
we know we're gonna beat it in here.
3:31
We'll do our if __name__ == '__main__' and
3:33
we can call app.run(debug=DEBUG,
3:39
host=HOST, and port=PORT).
3:44
So that way, if we need to change any of
those, we just change them up at the top.
3:49
We can easily turn off debug,
3:51
we can easily swap the host to something
else, whatever we wanna do.
3:53
And, you know what, let's also go ahead
and
3:57
just automatically insert a user or
ourselves.
4:00
Well actually, let's not worry about that,
we don't have the database initialized yet
4:05
so let's leave that part alone.
4:07
Having that global database will make it a
lot easier for
4:10
us if we decide to build our app with a
lot of different modules.
4:13
Like, maybe we'll have a views.py to hold
our views instead of doing them
4:16
all in the app file.
4:19
Remember when I said that we had more to
do with last login?
4:21
Let's handle that next bit in the next
video.
4:24
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up