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[MUSIC]

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[SOUND] We've solved the first problem.

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Let's move on to the second one.

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We need to implement a way for
our users to save their pizzas.

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To do this,

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we'll be using the Room library to store
pizza information in a SQLite database.

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Room makes maintaining a database
a lot easier than it used to be.

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Instead of having to write all the SQL
yourself, Room gives us a set of

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components that handle a lot of
that work behind the scenes.

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Let's take a minute to look
at these components and

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see how it all fits together.

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The first component of a RoomDatabase is
an entity, which represents a table and

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the database.

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Stepping up from an entity, we have data
access objects, also referred to as DAOs.

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A data access object is where we'll
keep all the queries we need for

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a specific table.

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At the very top is the RoomDatabase,
which groups together all of the DOAs and

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entities and provides a single
point of entry from within the app.

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We'll talk more about each
of those in just a bit.

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But before we can start on anything,

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we'll need to decide on
the structure of our database.

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What tables does it have?

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What columns are in those tables?

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And what relationships do we need
to maintain between columns?

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For us, we'll have a Pizza table and
a Toppings table.

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Both with id primary keys.

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But while this lets us
store some information,

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it's not giving us the whole story.

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We're missing out on which
toppings belong on which pizza.

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To get this information,
we'll need to add a third table

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to keep track of all the pizza and
topping combinations.

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This PizzaTopping table will
have two columns which are both

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foreign keys to other tables.

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And together, those two columns
also make up the primary key.

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If you'd like to read more about
why we need the PizzaTopping table,

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check out the article below on how
to handle a many-many relationship.

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Okay, now that we've got a better
idea of what we have to do,

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let's start building up from the bottom
and get to work on those entities.

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Heading back to Android Studio,

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I'll clean up my workspace a little
bit by closing all of these tabs.

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Then the first thing we need to do is
add a couple import statements for

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the Room library.

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Let's head over to our apps
build.gradle file and copy and

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paste in these two lines to the bottom
of the dependencies section.

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Also, they've been updating these
libraries somewhat frequently.

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So if you see a newer version warning,

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feel free to use Alt+Enter to
upgrade to the newest version.

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Then let's sync the project, And
now we can go about using our entities.

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Let's head over to the Pizza class and
add a line above the class declaration.

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And then type @Entity and
hit Enter to import it.

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And there we go,
our Pizza class is now a Pizza entity.

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However, all entities
require a primary key.

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So we're not quite done yet.

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To tell Room which column
is the primary key,

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we just need to add the @PrimaryKey
annotation before that column.

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Let's add a line above id and
then type, @PrimaryKey.

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You may need to use
Alt+Enter to import it.

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Awesome, that's it for our Pizza entity.

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Now let's update the Topping class.

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Let's add the @ entity annotation,
and then the @ primary key annotation.

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You could also put it on the same
line as the id if you prefer.

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Now that we've got Pizza and
Topping entities,

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it's time to create the PizzaTopping
entity, which we'll do in the next video.