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- [Instructor] Hi and
welcome back to the course!

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In this video we're going to be writing

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our items to the database.

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The first thing to do, however,

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I wanted to show you something

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that may become important in the future.

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And that is the way that
Python does the importing.

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See, when we import a file or, indeed,

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something from a file,
Python runs the file.

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So for example, here we are importing

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user register from user.

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So the first thing that Python does

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is it's going to run the user file

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and make sure that everything is in order.

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So it goes to the user file and it creates

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the class user and the class user register

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and it looks through the
methods and that sort of stuff.

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It doesn't actually run the methods.

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But, for example, if we
have a full stop there,

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it will identify that this is not correct.

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If we never import user, then it would not

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identify that that's not correct.

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It wouldn't run the file.

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So that's the first thing it does.

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It runs the file through.

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And if it's got any classes,

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then it verifies if the class is correct,

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if it's got any method,
it verifies the methods

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are correct, but it
doesn't actually run them.

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However, if it has a statement,

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such as a print statement
here, print "hello",

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every time we import this file,

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it runs that statement.

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And now that's interesting because

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imagine we have our user.py file here

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and we've made a lot of
code and at some point,

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we want to import something from app.py.

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For example, just for
the sake of imagination,

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imagine we want to import app

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so that see can get the secret key.

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Okay, not something that we're gonna do,

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but just imagine we have something here

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that we wanna import.

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All of these things would already exist

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if we've run the app.py file.

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For example, nowadays we do python app.py

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and that runs the app.py file.

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But if we run the user.py
file, for example,

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and that imports app, then on import

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we would run the
following statements here.

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Now, that may be okay.

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Because creating a flask
app is not a problem.

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Creating an API is not a problem.

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What is a problem, however, is running it.

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If we import something from
app.py and we want the app,

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then we can import the app
and everything is in order.

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We just create an object of type flask

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and then we import it.

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However, if we import from app,

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we would always run app.run,

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which means that on import

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we would start our flask application.

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And that's not really
what we want on an import.

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So on import, we don't want to do things

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that we would only wanna
do when we run the file.

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So here we only want to run the flask app

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if we say python app.py.

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If we are importing app,

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we don't wanna run the flask app

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because likely is that
we don't want to do that.

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So hopefully this makes a bit of sense.

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And fortunately, there
is a way that we can

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prevent the flask app from running

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if we were to import something from app.

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And that is: if
__name__=='__main__' and do that.

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I think we've looked
at this syntax before.

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I just wanted to explain
that this is why we do this.

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If we import app, then that creates

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the flask app, or if that already exists

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because Python's already run it,

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then it just gets the app from there.

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But if we import, then we would always run

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app.run which is not ideal.

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So this circumvents that because

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whenever you run a Python file,

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for example, if we do python app.py,

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Python assigns a special
name to the file we run

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and that name is always __main__.

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So if we run the app.py
file, that is main.

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If we run the user.py
file, then this is main.

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So only the file that you run is main

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and therefore, if the name is main,

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we know that we have run this file,

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and therefore we want
to start the flask app.

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If it's not main, then that means

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that we have imported
this file from elsewhere

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and therefore we don't
want to run the flask app.

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Okay, hopefully, this all makes sense.

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Now, leaving that aside, let's go

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into the post of our items.

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I'm gonna open item.py
and then we're gonna

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navigate down to the post method

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and we are gonna implement this, okay?

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So sorry for that sort of deviation,

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but I thought it was worth mentioning.

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Okay, so the first thing that we've got

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is something here which,
in the post method,

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which checks if an item already exists.

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Okay.

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So we should do that as well

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when we rewrite the method.

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This filters through the items list,

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which no longer exists,
now we need to make sure

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to check the database to see
if an item already exists.

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So how do we do that?

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Well, we've got the get
method which does that.

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However we cannot call the get method.

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We cannot say if get name,

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or rather if self.get
name because self.get

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requires a JWT token and
the post method does not.

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So then we would have a bunch of problems.

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So what we're gonna do
instead is we're going

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to extract some code from the get method

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into a separate method and then use that.

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So I'm gonna create a class method

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that is going to be find_by_name,

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and that's gonna be
taking cls and the name.

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Cls because it's a class
method with double s,

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and the name because that's
what we're gonna be finding

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and the find_my_name
method, all it's gonna do

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is it is going to do
all of this stuff there.

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So it's going to connect to the database,

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get a cursor, select
the item, run the query,

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fetch a row, close the connection,

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and then if the row exists,

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it's going to return the JSON.

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Now, the get method doesn't
have to be duplicated.

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So instead we can just say that the item

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is self.find_by_name,

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with the name and if item, return item.

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And if not item, then return not found.

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So now what we've done is we've extracted

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the useful code, essentially the code

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that doesn't deal with returning things.

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We've extracted that
into a separate method

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which means that we can now call it

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from our post method.

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Instead of if self.get, we
say if self.find_by_name.

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And I do appreciate that
this is a class method

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and not sort of a self
method, like post is,

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but nevertheless we can
still call it using self.,

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or we could call it using
Item., if you prefer.

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It doesn't really matter, either is fine.

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Okay.

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So there we go.

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Now we are able to return that an item

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with the name already
exists, if it already exists.

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Okay.

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Now let's go below and
what we have to change

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is this items.append.

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Now, items.append is only useful

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if we have a list that we can append to.

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Now we are gonna have to
write it to the database.

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So what to do is you guessed it.

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First of all we connect,

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data.db and we create a cursor.

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I'm sure you remember how
to do all this stuff by now.

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Then we create a query which is gonna be

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insert into items the values,
question mark, question mark,

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but this is gonna the name and the price.

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Then we are going to execute the query

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with the item's name and price.

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We've defined the item up here,

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just as we had in the last section,

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so we're just gonna use that item's name

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and the item's price.

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Okay.

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And once we've inserted the item there,

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all we have to do is close it,

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well, commit it and close it.

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And then we return the item
which is this JSON here.

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Remember we cannot return item objects

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or user objects, we
always have to return JSON

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and the item here is a piece of JSON data.

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Okay, so that's our item.

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Let's go ahead and run this.

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So, the first thing I'm gonna do actually

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is go to the create_tables file

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and remove the test data from there.

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So don't insert test data anymore,

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we don't need the test data

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since we are now able to insert data.

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Now let's go over to the terminal.

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For me this restarts automatically.

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But if it doesn't, then you
can restart it yourself.

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What I'm gonna do is
remove the data.db file.

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You can do that through
Atom if you prefer,

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just right click and remove,

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or you can do it on the terminal like so,

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and then run the app again.

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Now remember, because we've run the app

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that is __main__, so it
starts the flask server.

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And then let's go over to Postman

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and I am going to close that,

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and the first thing that
we have to do, remember,

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is register because we
don't have any users

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so I'm gonna register there.

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And of course, if you delete, apologies.

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We have deleted data.db so we also have

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to create the tables again.

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My bad.

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Easy to forget to do that.

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Just remember that if it tells you

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sqlite3.OperationalError,
no such table users,

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you know that you forgot
to create the tables.

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Okay, let's try that again.

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We create the user.

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Then let's go over to auth and sign up,

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sing in rather, copy the access token,

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create a new item which
I'm gonna call test,

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and the item is there created.

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This endpoint doesn't need the JW Token

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but just to verify we are going to get

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the item out and indeed it comes out.

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So now we're able to write data

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to the database as well,
which we already were

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with the user but
nevertheless just going over

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through the motions once again.

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So what we're doing first is we check

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the item's not already in the database

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and then we parse the
data using the parser,

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which, as you know, checks for price.

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We create a JSON of the item and then

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we use that to insert into the database.

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And finally we return the item there.

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So there's nothing magical going on here

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and in fact many, many, many REST APIs

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like this one are just this,

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are what's called CRUD APIs:
create, read, update, delete.

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That's what this item
resource does essentially.

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Create, read, update is down
here, the put, and delete.

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And it's really this simple.

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I'm sure you could go ahead and implement

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and delete and put yourselves as well.

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There's really no much
magic going into it,

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just a couple of SQL statements.

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And that's it.

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And if you have stores as well as items,

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then you would also have a store resource

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that has these four methods,

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and they're all very, very similar.

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You can also get much
more complicated APIs,

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of course, that do other
things, like send emails

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or look for flights
even, things like that.

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But in many cases you will be creating

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CRUD APIs like this one
and, as you can see,

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there's no magic going on.

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It's just a matter of
interacting with the database

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and putting things in
it or taking things out.

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So it's not too complicated.

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It's just a matter of writing
the code to do it really.

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But there's nothing
difficult inherently in it.

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Anyway, I hope you feel that way as well

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because if not, that
would be rather awkward.

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So if you do think that this is difficult,

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do ask a question because the process

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for inserting, retrieving
data and the interactions

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are inherently simple,
there's not much going on.

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So if you think it is,
then do ask a question,

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I'm always eager to help out.

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And that's it for this video.

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So I'll see you in the very next one.