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So what I'd like to do
is somehow tell Django | 3,095.53 | 3.06 |
that you should update the database to
include information about the models | 3,098.59 | 4.17 |
that I have just created. | 3,102.76 | 1.5 |
This is a process that we refer
to in Django and more generally as | 3,104.26 | 3.15 |
migrations. | 3,107.41 | 1.24 |
I create a migration to
say, here are some changes | 3,108.65 | 3.05 |
that I would like to
apply to the database. | 3,111.7 | 2.37 |
Then I migrate them to tell
Django to take those changes | 3,114.07 | 3.6 |
and actually apply them to the database. | 3,117.67 | 2.18 |
So it's a 2-step process. | 3,119.85 | 1.33 |
One is creating the migration, the
instructions for how to actually go | 3,121.18 | 3.93 |
about manipulating the database. | 3,125.11 | 1.5 |
And then one to take that migration step
of saying now take those instructions | 3,126.61 | 4.29 |
and actually apply them to
the underlying database. | 3,130.9 | 3.9 |
We can make the migrations via command. | 3,134.8 | 2.52 |
Again we'll use the manage.py script
that has a number of different commands | 3,137.32 | 3.66 |
that allow us to control various
parts of the application. | 3,140.98 | 2.85 |
I'll use python manage .py
and then MAKE migrations. | 3,143.83 | 5.46 |
Now what we see is we've created a
migration inside of 0001_initial.py | 3,149.29 | 6.3 |
where in this migration it's
created a model called "flight." | 3,155.59 | 5.06 |
So if I go ahead and look
at the migrations directory, | 3,160.65 | 3.22 |
I see this file has been created for me. | 3,163.87 | 2.89 |
I didn't have to create it myself. | 3,166.76 | 1.85 |
This file has instructions
to Django for how | 3,168.61 | 3.72 |
to manipulate the database to reflect
the changes I have made to the model. | 3,172.33 | 4.47 |
Here is an instruction to Django
to create a new model called | 3,176.8 | 3.75 |
"flight" that has these
particular fields inside of it. | 3,180.55 | 3.75 |
It's basing this off of the
changes that I made to models.py. | 3,184.3 | 3.39 |
The model that I added is now
reflected in this migration. | 3,187.69 | 4.59 |
Now if I want to apply the migration,
actually apply it to Django's database, | 3,192.28 | 4.47 |
I can run python manage.py MIGRATE to
go ahead and apply these migrations. | 3,196.75 | 5.542 |
There are a bunch of default
migrations that get applied as well, | 3,202.292 | 2.708 |
but notice that one of the migrations
that gets applied is this one here. | 3,205 | 3.87 |
Applying flights.0001_initial to
say let's go ahead and apply that | 3,208.87 | 5.1 |
migration, create that table that
is going to represent flights. | 3,213.97 | 4.53 |
If I type LS now, you'll see that
now I have a db.sqlite3 file. | 3,218.5 | 5.37 |
A SQLite database that is
going to contain a table that | 3,223.87 | 3.72 |
is going to store all of my flights. | 3,227.59 | 2.827 |
And so how can I actually
begin to manipulate this data? | 3,230.417 | 2.333 |
How can I interact with
these sorts of models? | 3,232.75 | 3.72 |
I could use direct SQL syntax
by opening up this database file | 3,236.47 | 3.51 |
and running commands, but Django
provides some nice abstraction layers | 3,239.98 | 3.51 |
on top of it so that I don't actually
need to execute those commands myself. | 3,243.49 | 3.63 |
I can begin to work more generally with
Python classes and variables and things | 3,247.12 | 4.41 |
that I'm used to inside
the Python language. | 3,251.53 | 2.88 |
So I can enter Django's shell where
I can just run Python commands | 3,254.41 | 3.757 |
by running python manage.py shell. | 3,258.167 | 1.417 |
What this does is open
up a shell or a console | 3,262.75 | 1.92 |
where I can begin to
write Python commands that | 3,264.67 | 3.03 |
get executed on this web application. | 3,267.7 | 2.67 |
The first thing I'd like to
do is from flights.models | 3,270.37 | 3.99 |
let me just import flight. | 3,274.36 | 2.66 |
So "flights" is the name of my app. | 3,277.02 | 1.48 |
"Models" is the name of that file. | 3,278.5 | 1.74 |
I'm importing the flight class from
that models file that I've just created. | 3,280.24 | 4.53 |
Now what I can do is I
can create a new flight. | 3,284.77 | 3.54 |
I can say something like f= a
flight whose origin is "New York" | 3,288.31 | 5.88 |
and whose destination is "London"
and whose duration= 415 minutes. | 3,294.19 | 6.63 |
And then I can say f.save to save
that new flight that I have created. | 3,300.82 | 4.442 |
This syntax-- I'll go ahead and make it
a little bit bigger so you can see it | 3,305.262 | 3.208 |
a little easier-- | 3,308.47 | 0.99 |
is my way of inserting
data into this table. | 3,309.46 | 3.67 |
I don't need to use an
INSERT query in SQL. | 3,313.13 | 2.39 |
I just have to write a Python
command, and Django knows that when | 3,315.52 | 3.09 |
I create a new flight and save it,
that it should run an instant command | 3,318.61 | 4.14 |
on the underlying SQL tables. | 3,322.75 | 1.59 |
Where here I've created a new
flight with this particular origin | 3,324.34 | 3.57 |
and destination and duration and I've
gone ahead and saved that flight as | 3,327.91 | 4.11 |
well. | 3,332.02 | 1.04 |
If I want to query that flight,
get information about that flight, | 3,333.06 | 3.1 |
I can say something
like, flight.objects.all | 3,336.16 | 4.08 |
is the equivalent of a Select-All. | 3,340.24 | 1.77 |
Get me all of the flights that
exist inside of my database. | 3,342.01 | 4.38 |
Here I see I get back a query set,
which is just a set of results. | 3,346.39 | 4.35 |
Here I have one flight that
came back, flight object 1. | 3,350.74 | 3.33 |
So a flight has been
created for me with ID 1. | 3,354.07 | 2.76 |
Now "flight object 1" probably
not all that helpful of a name. | 3,356.83 | 3.12 |
It'd be nicer if this
model had a cleaner | 3,359.95 | 2.16 |
way of seeing the name of a
particular flight, for example. | 3,362.11 | 4.23 |
And it turns out we can do that. | 3,366.34 | 1.8 |
Any model-- I'll go back to
the code inside of models.py-- | 3,368.14 | 3.54 |
any model can implement
double underscore str | 3,371.68 | 3.84 |
function, which returns
a string representation | 3,375.52 | 4.2 |
of that particular object. | 3,379.72 | 1.89 |
This applies not just to Django models
but to Python classes more generally. | 3,381.61 | 3.48 |
That if this function returns a
string representation of the object, | 3,385.09 | 3.31 |
let's go ahead and return a
formatted string that is self.id | 3,388.4 | 4.7 |
I'll say self.origin
to self.destination. | 3,393.1 | 4.32 |
So here what I've said is that the
string representation of any flight | 3,397.42 | 4.11 |
is going to be a string that gives its
ID and then says origin to destination. | 3,401.53 | 4.5 |
Just a nice clean name that is going
to represent this particular flight. | 3,406.03 | 4.77 |
So now if I go back to the shell
by running python manage.py shell, | 3,410.8 | 6.35 |
I can say from
flights.models import Flight. | 3,417.15 | 3.508 |
I can say, all right,
let's let a variable called | 3,420.658 | 2.042 |
flights be equal to flight.objects.all. | 3,422.7 | 3.66 |
And now flights is going to be this
flight, flight 1, New York to London. | 3,426.36 | 5.4 |
It now has a much nicer,
string representation | 3,431.76 | 2.22 |
of the name, which just makes it a
little bit easier to interact with. | 3,433.98 | 3.69 |
If I wanted to get just that one flight,
I can say flight equals flights.first. | 3,437.67 | 5.34 |
Flights is a query set. | 3,443.01 | 1.47 |
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