text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
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There are a number of
unexpected results that | 2,787.35 | 1.96 |
can happen when we deal with
problems related to race conditions | 2,789.31 | 3.3 |
where multiple things are
happening simultaneously. | 2,792.61 | 2.83 |
How do we solve those problems? | 2,795.44 | 1.49 |
Well, one strategy is to sort
of place a lock on the database. | 2,796.93 | 3.3 |
To say, while I'm working
on this database nobody else | 2,800.23 | 2.88 |
can touch this data. | 2,803.11 | 1.18 |
Let me finish this
transaction, so to speak. | 2,804.29 | 2.29 |
Finish working on this particular
transaction and making all the changes | 2,806.58 | 3.31 |
I need to make to the database. | 2,809.89 | 1.47 |
Only after I'm done I can release the
lock and let someone else go ahead | 2,811.36 | 4.26 |
and modify the database as well. | 2,815.62 | 2.1 |
So a number of concerns
to be aware of as we | 2,817.72 | 2.37 |
begin dealing in this world of SQL
and trying to work with databases. | 2,820.09 | 5.43 |
So now that we've taken a
look at the syntax of SQL, | 2,825.52 | 2.28 |
understanding how these tables
work, how they're structured, | 2,827.8 | 3.03 |
and what it is that we
can add to those tables, | 2,830.83 | 2.23 |
let's go ahead and turn our
attention in particular to Django | 2,833.06 | 3.05 |
models, which are a way of representing
data inside of a Django application. | 2,836.11 | 4.098 |
Because where Django is really going
to get powerful in designing our web | 2,840.208 | 3.042 |
applications is the ability to
represent data in terms of these models. | 2,843.25 | 4.468 |
So we're going to go ahead and try
to create a web application that | 2,847.718 | 2.792 |
is going to represent what an
airline might want to store inside | 2,850.51 | 3.9 |
of its own web application. | 2,854.41 | 2.7 |
All right. | 2,857.11 | 0.5 |
So the first thing I want to
do is create a Django project. | 2,857.61 | 3.16 |
So I'll go ahead and type
Django-admin START PROJECT | 2,860.77 | 2.955 |
and the name of my project
will just be called "airline." | 2,863.725 | 2.375 |
I'm creating a project for an
airline's website for example. | 2,866.1 | 3.37 |
I'll go ahead and go into
the airline directory, | 2,869.47 | 2.06 |
open that up in my code editor. | 2,871.53 | 1.78 |
Before I actually
begin editing any code, | 2,873.31 | 2.37 |
remember that every Django project needs
to have one or more apps within it. | 2,875.68 | 4.32 |
So the first app that I'll
create for this airline | 2,880 | 2.61 |
is an app for keeping track of flights. | 2,882.61 | 3.15 |
So keeping track of flight
related information, | 2,885.76 | 2.7 |
like origins and
destinations and durations | 2,888.46 | 2.31 |
and what passengers
are on those flights. | 2,890.77 | 2.91 |
When I create a new app,
first thing I'll need to do | 2,893.68 | 2.97 |
is go into settings.py
inside of airline, | 2,896.65 | 2.88 |
and go ahead and add this
app as an installed app. | 2,899.53 | 3.36 |
So "flights" is now an
app that I have installed. | 2,902.89 | 3.15 |
Then what I'll want to do is say, go
ahead and go into urls.py, which is, | 2,906.04 | 6.662 |
again, that table of
contents for all the | 2,912.702 | 1.708 |
URLs I can get to for this
particular web application. | 2,914.41 | 2.46 |
I'll IMPORT include, because I want
to do is when someone visits the path | 2,916.87 | 4.29 |
of flights/ something, I want
to take them to flights.urls, | 2,921.16 | 5.56 |
mapping them to the urls.py file
that will be inside of my "flights" | 2,926.72 | 4.82 |
application. | 2,931.54 | 1.41 |
Of course, now I need a urls.py file
inside of my "flights" application. | 2,932.95 | 4.01 |
So I go into "flights" and create
a new file that I'll call urls.py. | 2,936.96 | 4.09 |
We can do from FROM.django.urls
IMPORT path FROM .IMPORT views. | 2,943.87 | 5.34 |
And then my URL patterns are going
to go inside of this list right here. | 2,949.21 | 4.9 |
But before I begin
dealing with actual URLs, | 2,954.11 | 2.15 |
the first thing I'm going to
want to do is create some models. | 2,956.26 | 3.28 |
Models are going to be a way
of creating a Python class that | 2,959.54 | 2.93 |
is going to represent data that I want
Django to store inside of a database. | 2,962.47 | 4.62 |
So when I create a
model, Django is going | 2,967.09 | 1.77 |
to figure out what SQL syntax it needs
to use it to A-- create that table | 2,968.86 | 4.08 |
but then B-- manipulate that table. | 2,972.94 | 1.8 |
Selecting and updating and inserting
anytime I make changes to those models. | 2,974.74 | 4.71 |
So here what I can do is inside
of every app that gets created-- | 2,979.45 | 3.54 |
in this case called "flights"--
there is a models.py file. | 2,982.99 | 3.35 |
We haven't looked at
this before, but this | 2,986.34 | 1.75 |
is going to be the place where
we get to define what models | 2,988.09 | 2.98 |
are going to exist for our application. | 2,991.07 | 2.79 |
Every model is going
to be a Python class. | 2,993.86 | 2.31 |
You can think of this as having one
model for each of the main tables | 2,996.17 | 3.39 |
we care about storing information about. | 2,999.56 | 2.62 |
So let me define a new
class called "flight" | 3,002.18 | 2.42 |
that is going to inherit from models
dot model some creating a new class | 3,004.6 | 3.48 |
called "flight" that
is going to be a model. | 3,008.08 | 3.75 |
Then I need to provide inside of
this class all of the parameters | 3,011.83 | 3.69 |
that a flight has. | 3,015.52 | 0.77 |
What properties does a flight have
that I might want to keep track of? | 3,016.29 | 3.76 |
Well, a flight has an origin. | 3,020.05 | 2.13 |
And the origin is going
to be a models.charfield. | 3,022.18 | 3.51 |
This is all documented
on Django's website | 3,025.69 | 1.83 |
in terms of the various different
types of fields that exist that I | 3,027.52 | 3.3 |
can include inside of a Django model. | 3,030.82 | 2.25 |
Where here I'm saying
here is a character field | 3,033.07 | 2.71 |
whose max length is going to be 64. | 3,035.78 | 3.34 |
I assume that most city names are not
going to go longer than 64 characters. | 3,039.12 | 3.34 |
That seems like a reasonable maximum
length for the origin of the flight, | 3,042.46 | 3.72 |
for example. | 3,046.18 | 1.32 |
Every flight will also
have a destination, | 3,047.5 | 1.98 |
which will be a character field
whose max length is also 64. | 3,049.48 | 4.41 |
Every flight will have a duration,
which will just be an integer field. | 3,053.89 | 4.68 |
So now this is my very
first Django model. | 3,058.57 | 3.03 |
It is a class called "flight" where
I've defined all of the properties | 3,061.6 | 3.87 |
that a flight has, and then
using Django syntax to find | 3,065.47 | 2.85 |
what type they should have as well. | 3,068.32 | 1.56 |
Every flight has an origin, has a
destination, and has a duration. | 3,069.88 | 5.31 |
But of course nothing
here is actually modified | 3,075.19 | 2.07 |
the database the Django is using
in order to store information | 3,077.26 | 3.93 |
about my web application. | 3,081.19 | 1.2 |
And we can see if we, in
fact go back to airline, | 3,082.39 | 2.32 |
and I type LS, what you see here is that
there isn't yet a database that exists. | 3,084.71 | 5.61 |
I just have an airline
directory, a flights directory, | 3,090.32 | 2.69 |
and a manage.py file. | 3,093.01 | 2.52 |
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