Back-End Programming Exam > Back-End Programming Videos > Django: The Ultimate Beginners Guide > Django Tutorial for Beginners - 7 - Creating Models
Django Tutorial for Beginners - 7 - Creating Models Video Lecture | Django: The Ultimate Beginners Guide - Back-End Programming
FAQs on Django Tutorial for Beginners - 7 - Creating Models Video Lecture - Django: The Ultimate Beginners Guide - Back-End Programming
| 1. What is Django and why is it used? |  |
Ans. Django is a high-level Python web framework that allows developers to rapidly build web applications. It follows the model-view-controller (MVC) architectural pattern and provides a set of tools and libraries for handling common web development tasks. Django is used for its scalability, security, and reusability, making it popular among developers for creating robust and maintainable web applications.
| 2. What are models in Django and how do they relate to databases? | |
Ans. In Django, models are Python classes that represent database tables. They define the structure of the data and the relationships between different objects. Models in Django provide an abstraction layer over the database, allowing developers to interact with the database using Python code without directly writing SQL queries. Django takes care of creating and managing the database tables based on the models defined in the application.
| 3. How do you create a model in Django? | |
Ans. To create a model in Django, you need to define a Python class that subclasses the `django.db.models.Model` class. Inside the class, you define different fields that represent the columns in the database table. Each field is defined as a class attribute with the corresponding data type. You can also specify various options for each field, such as maximum length, default values, and relationships with other models. Once the model is defined, you can use Django's migration system to create the corresponding database table.
| 4. What is the purpose of migrations in Django? | |
Ans. Migrations in Django are a way to manage changes to the database schema over time. When you make changes to the models or the database structure, Django generates migration files that capture those changes. These migration files contain the instructions to modify the database schema, such as creating or altering tables, adding or removing columns, and creating relationships between tables. You can apply these migrations to the database to keep it in sync with the models defined in your Django application.
| 5. How does Django handle database relationships between models? | |
Ans. Django provides different types of fields to handle database relationships between models. The most commonly used ones are `ForeignKey` and `ManyToManyField`.
- `ForeignKey` represents a one-to-many relationship, where one model has a foreign key to another model. For example, if a `Book` model has a foreign key to an `Author` model, it means that an author can have multiple books, but a book can have only one author.
- `ManyToManyField` represents a many-to-many relationship, where multiple models can be related to multiple other models. For example, if a `Student` model has a many-to-many relationship with a `Course` model, it means that a student can enroll in multiple courses, and a course can have multiple students.
Django handles these relationships by creating the necessary database tables and providing convenient methods and queries to access and manipulate the related objects.
Text Transcript from Video
already houses welcome back and in this
video everything is going to start to
make sense and come together and
hopefully you guys are going to have a
lot of ah I see what's going on now
those kind of moments so what we're
going to be doing is we're going to be
creating our models for our music app
now a model is just a blueprint of how
you want to store your data so what
kinds of data are going to be saving
well we're going to be saving albums and
songs so we need to build blueprints in
for example we're just going to say ok
the album needs a title in a genre and
like an artist and stuff like that now
if you guys are like alright you're
going to create these blueprints but are
you talking about like for the database
or for your actual Python code well this
is the cool thing whenever you can make
models in Django it's the same thing you
don't have to make one for your database
and then say okay now I have to
configure this with my actual code no no
you just make a class right in here and
automatically what jingle is going to do
is it's going to get each variable from
those class and convert it to it a
column in your database so it's actually
pretty amazing so open up
music models and we're currently create
our very first class which is class
album now every model or blueprint you
create it has to inherit from models dot
model alright so again all you do inside
these classes is you're just going to
create variables so what does each album
have I'll just go ahead and write artist
equals in this variable name again we're
just writing a regular Python class so
again we can just work with it in Python
but later on whenever we migrate it over
its database this is actually going to
be the same name is a column so we don't
have to write it twice
Django takes care of all of that for us
pretty sweet so after this what we do is
we actually set this equal to models and
then the one thing that we need to tell
Django is what type of data is this
variable going to hold is it going to
hold text or is it going to hold a float
or is it going to hold an integer or
maybe something weird well for this
tutorial I'm just going to keep things
as simple as possible and of course the
artist name is just a bunch of text so
that would be a char field so the one
thing that we need to specify whenever
we are storing characters or just text
is just a max length so we'll say max
length equals how long are people's
names
250 I guess I don't know they probably
aren't even close to that long but
whatever
all right so for each album we need to
go ahead and write the artist name
whether it's a band or you know just
like artists like Taylor Swift or
whatever and what else let's just go
ahead and write album title so Liz
Taylor Swift's last album don't even
know what it was I know red red was one
and then she had another one named
Taylor Swift so uh yeah so that's what
you know would be an example of this and
just like before this is also just going
to be characters and I don't know is the
album title the same length maybe they
were longer so we'll say that we can
have 500 characters for that now another
thing that we can do is store the genre
whether it's country rap whatever so
models garfield max length equals I
don't know 100 i'll thing any genres are
more than 100 characters and I actually
thought it would be pretty cool is
whenever we're making our website if for
each album then it had a logo but I
didn't teach you guys how to upload
files yet eventually we're going to be
doing that so right now we're just going
to have to post the link and that's how
we'll display it we'll just find some
image online and use that link of the
image so just say album logo
equal curfew and and we'll say max
length equals a thousand since maybe
some of these URLs are going to be kind
of big all right so this is what an
album is going to be made up of so
whenever we're using it in Python we
just use these variables whenever we
have to you know like set the album
title in something and also later on
whenever we look at this in the database
the actual column name is going to be
artists so all that is taken care of
behind the scenes it's going to be cool
now after this I'm going to go ahead and
create one more class and I'm just going
to name this song so just like before
and since I'm too lazy to type all that
I'm just going to go ahead and paste
that now check this out so we actually
need to associate these in some kind of
way so we can go ahead and create as
many albums as we want and they can just
be you know kind of their own thing but
whenever we create a song it needs to be
associated with an album in other words
a song needs to be part of an album so
usually we're going to have like 12 or
15 songs per album so how do we link
these together in that kind of way well
what we can do is this if we make
variable called album you can go ahead
and write models and instead of just car
field you can write foreign key now let
me go ahead and type this real quick and
explain what this means on delete models
the Cascade alright so and again alright
so first of all let's go ahead and talk
about primary keys so you know that I
said that whenever we create this in our
database we're going to have these four
columns right there but actually behind
the scenes Django is going to make
another column for us and this is pretty
much a unique ID number so the very
first album we create it's going to give
it the ID of one when we carry another
one it's going to give it the ID of two
so on and so forth and
each additional album that we add it's
going to increment it by one so why does
it do that I mean whenever we just try
to pick out an ohm out there we can just
say hey give me that album read
well what if not only Taylor Swift has a
album called read but a couple other
bands do as well well then it's going to
get confused alright so let's just say
okay give me the albums by Taylor Swift
well Taylor Swift probably has like 12
albums or whatever so it's just a mess
if you have all of these pieces of
information you don't know what you want
to specify so whenever you have a row in
the database it's always good to have a
unique ID number now since one album can
only have its ID number in other words
two albums can't both have the ID number
of five that's why you call it a primary
or unique key so that's what that is and
that's what these albums are going to
have behind the scenes alright so what
is this foreign key that's kind of weird
alright so each song is going to be
linked to an album so we'll say that the
album read has the primary key of one so
basically whenever we create a song says
Taylor Swift I don't know like I hate my
boyfriend over at ever we need to link
it to an album so the key the foreign
key for this is just going to be one and
that way we know that this song whatever
song we said is linked to the album one
which is read so again a primary key is
just needed whenever you have a bunch of
elements in the east need a unique ID
number a foreign key is used whenever
you have something like a song that's
part of something else so you just give
it the ID number of whatever it belongs
to and that's what a foreign key is now
the only other thing you guys may not
know is this on delete models cascade
what this means is all right since
you're going to have a bunch of songs
and they need to be part of an elbow
what happens whenever you delete that
album well you just can't have a bunch
of songs though because again that
doesn't make sense you can't have songs
that are on any album at least not in
this you know kind of program so we're
going to say models cascade on delete
which means whenever we delete the album
read any songs that were linked to that
then go ahead and delete those as well
you actually can set it up in some
programs where you can say okay it's
actually okay to delete these things and
these things might still exist um I
don't know maybe you had like a forum
post and you wanted to delete it but all
the answers are really good so you want
to keep them or something so that may be
an example but I don't getting kind of
head of myself anyways moving on nothing
you guys at that little primer alright
another thing I want to store in here is
file type and this can just be like um
mp3 or I don't know what's another away
file whatever weird ones Apple has and
we're just going to store those is uh
okay my caps lock is on and I'm too lazy
to do that anyway so a file type mp3 avi
or not avi WAV I don't think any file
types are longer than ten characters so
we should be safe there now the last
thing we should probably have is the
song title that's pretty important a so
models get for your max how long is the
title 250 any titles longer than 250
then whatever re looking good mate
looking good so albums you have all the
information that we want in their songs
okay we have the album that it's linked
to the file type in the song title look
good so alright
video everything is going to start to
make sense and come together and
hopefully you guys are going to have a
lot of ah I see what's going on now
those kind of moments so what we're
going to be doing is we're going to be
creating our models for our music app
now a model is just a blueprint of how
you want to store your data so what
kinds of data are going to be saving
well we're going to be saving albums and
songs so we need to build blueprints in
for example we're just going to say ok
the album needs a title in a genre and
like an artist and stuff like that now
if you guys are like alright you're
going to create these blueprints but are
you talking about like for the database
or for your actual Python code well this
is the cool thing whenever you can make
models in Django it's the same thing you
don't have to make one for your database
and then say okay now I have to
configure this with my actual code no no
you just make a class right in here and
automatically what jingle is going to do
is it's going to get each variable from
those class and convert it to it a
column in your database so it's actually
pretty amazing so open up
music models and we're currently create
our very first class which is class
album now every model or blueprint you
create it has to inherit from models dot
model alright so again all you do inside
these classes is you're just going to
create variables so what does each album
have I'll just go ahead and write artist
equals in this variable name again we're
just writing a regular Python class so
again we can just work with it in Python
but later on whenever we migrate it over
its database this is actually going to
be the same name is a column so we don't
have to write it twice
Django takes care of all of that for us
pretty sweet so after this what we do is
we actually set this equal to models and
then the one thing that we need to tell
Django is what type of data is this
variable going to hold is it going to
hold text or is it going to hold a float
or is it going to hold an integer or
maybe something weird well for this
tutorial I'm just going to keep things
as simple as possible and of course the
artist name is just a bunch of text so
that would be a char field so the one
thing that we need to specify whenever
we are storing characters or just text
is just a max length so we'll say max
length equals how long are people's
names
250 I guess I don't know they probably
aren't even close to that long but
whatever
all right so for each album we need to
go ahead and write the artist name
whether it's a band or you know just
like artists like Taylor Swift or
whatever and what else let's just go
ahead and write album title so Liz
Taylor Swift's last album don't even
know what it was I know red red was one
and then she had another one named
Taylor Swift so uh yeah so that's what
you know would be an example of this and
just like before this is also just going
to be characters and I don't know is the
album title the same length maybe they
were longer so we'll say that we can
have 500 characters for that now another
thing that we can do is store the genre
whether it's country rap whatever so
models garfield max length equals I
don't know 100 i'll thing any genres are
more than 100 characters and I actually
thought it would be pretty cool is
whenever we're making our website if for
each album then it had a logo but I
didn't teach you guys how to upload
files yet eventually we're going to be
doing that so right now we're just going
to have to post the link and that's how
we'll display it we'll just find some
image online and use that link of the
image so just say album logo
equal curfew and and we'll say max
length equals a thousand since maybe
some of these URLs are going to be kind
of big all right so this is what an
album is going to be made up of so
whenever we're using it in Python we
just use these variables whenever we
have to you know like set the album
title in something and also later on
whenever we look at this in the database
the actual column name is going to be
artists so all that is taken care of
behind the scenes it's going to be cool
now after this I'm going to go ahead and
create one more class and I'm just going
to name this song so just like before
and since I'm too lazy to type all that
I'm just going to go ahead and paste
that now check this out so we actually
need to associate these in some kind of
way so we can go ahead and create as
many albums as we want and they can just
be you know kind of their own thing but
whenever we create a song it needs to be
associated with an album in other words
a song needs to be part of an album so
usually we're going to have like 12 or
15 songs per album so how do we link
these together in that kind of way well
what we can do is this if we make
variable called album you can go ahead
and write models and instead of just car
field you can write foreign key now let
me go ahead and type this real quick and
explain what this means on delete models
the Cascade alright so and again alright
so first of all let's go ahead and talk
about primary keys so you know that I
said that whenever we create this in our
database we're going to have these four
columns right there but actually behind
the scenes Django is going to make
another column for us and this is pretty
much a unique ID number so the very
first album we create it's going to give
it the ID of one when we carry another
one it's going to give it the ID of two
so on and so forth and
each additional album that we add it's
going to increment it by one so why does
it do that I mean whenever we just try
to pick out an ohm out there we can just
say hey give me that album read
well what if not only Taylor Swift has a
album called read but a couple other
bands do as well well then it's going to
get confused alright so let's just say
okay give me the albums by Taylor Swift
well Taylor Swift probably has like 12
albums or whatever so it's just a mess
if you have all of these pieces of
information you don't know what you want
to specify so whenever you have a row in
the database it's always good to have a
unique ID number now since one album can
only have its ID number in other words
two albums can't both have the ID number
of five that's why you call it a primary
or unique key so that's what that is and
that's what these albums are going to
have behind the scenes alright so what
is this foreign key that's kind of weird
alright so each song is going to be
linked to an album so we'll say that the
album read has the primary key of one so
basically whenever we create a song says
Taylor Swift I don't know like I hate my
boyfriend over at ever we need to link
it to an album so the key the foreign
key for this is just going to be one and
that way we know that this song whatever
song we said is linked to the album one
which is read so again a primary key is
just needed whenever you have a bunch of
elements in the east need a unique ID
number a foreign key is used whenever
you have something like a song that's
part of something else so you just give
it the ID number of whatever it belongs
to and that's what a foreign key is now
the only other thing you guys may not
know is this on delete models cascade
what this means is all right since
you're going to have a bunch of songs
and they need to be part of an elbow
what happens whenever you delete that
album well you just can't have a bunch
of songs though because again that
doesn't make sense you can't have songs
that are on any album at least not in
this you know kind of program so we're
going to say models cascade on delete
which means whenever we delete the album
read any songs that were linked to that
then go ahead and delete those as well
you actually can set it up in some
programs where you can say okay it's
actually okay to delete these things and
these things might still exist um I
don't know maybe you had like a forum
post and you wanted to delete it but all
the answers are really good so you want
to keep them or something so that may be
an example but I don't getting kind of
head of myself anyways moving on nothing
you guys at that little primer alright
another thing I want to store in here is
file type and this can just be like um
mp3 or I don't know what's another away
file whatever weird ones Apple has and
we're just going to store those is uh
okay my caps lock is on and I'm too lazy
to do that anyway so a file type mp3 avi
or not avi WAV I don't think any file
types are longer than ten characters so
we should be safe there now the last
thing we should probably have is the
song title that's pretty important a so
models get for your max how long is the
title 250 any titles longer than 250
then whatever re looking good mate
looking good so albums you have all the
information that we want in their songs
okay we have the album that it's linked
to the file type in the song title look
good so alright
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