The Parts of a Room Database

[MUSIC] 0:00 [SOUND] We've solved the first problem. 0:03 Let's move on to the second one. 0:06 We need to implement a way for our users to save their pizzas. 0:08 To do this, 0:12 we'll be using the Room library to store pizza information in a SQLite database. 0:12 Room makes maintaining a database a lot easier than it used to be. 0:17 Instead of having to write all the SQL yourself, Room gives us a set of 0:21 components that handle a lot of that work behind the scenes. 0:25 Let's take a minute to look at these components and 0:28 see how it all fits together. 0:31 The first component of a RoomDatabase is an entity, which represents a table and 0:32 the database. 0:37 Stepping up from an entity, we have data access objects, also referred to as DAOs. 0:38 A data access object is where we'll keep all the queries we need for 0:44 a specific table. 0:47 At the very top is the RoomDatabase, which groups together all of the DOAs and 0:49 entities and provides a single point of entry from within the app. 0:54 We'll talk more about each of those in just a bit. 0:58 But before we can start on anything, 1:00 we'll need to decide on the structure of our database. 1:03 What tables does it have? 1:05 What columns are in those tables? 1:07 And what relationships do we need to maintain between columns? 1:08 For us, we'll have a Pizza table and a Toppings table. 1:13 Both with id primary keys. 1:16 But while this lets us store some information, 1:19 it's not giving us the whole story. 1:21 We're missing out on which toppings belong on which pizza. 1:23 To get this information, we'll need to add a third table 1:27 to keep track of all the pizza and topping combinations. 1:29 This PizzaTopping table will have two columns which are both 1:33 foreign keys to other tables. 1:36 And together, those two columns also make up the primary key. 1:38 If you'd like to read more about why we need the PizzaTopping table, 1:42 check out the article below on how to handle a many-many relationship. 1:47 Okay, now that we've got a better idea of what we have to do, 1:51 let's start building up from the bottom and get to work on those entities. 1:54 Heading back to Android Studio, 1:58 I'll clean up my workspace a little bit by closing all of these tabs. 2:00 Then the first thing we need to do is add a couple import statements for 2:04 the Room library. 2:08 Let's head over to our apps build.gradle file and copy and 2:10 paste in these two lines to the bottom of the dependencies section. 2:13 Also, they've been updating these libraries somewhat frequently. 2:18 So if you see a newer version warning, 2:22 feel free to use Alt+Enter to upgrade to the newest version. 2:24 Then let's sync the project, And now we can go about using our entities. 2:28 Let's head over to the Pizza class and add a line above the class declaration. 2:35 And then type @Entity and hit Enter to import it. 2:42 And there we go, our Pizza class is now a Pizza entity. 2:46 However, all entities require a primary key. 2:51 So we're not quite done yet. 2:55 To tell Room which column is the primary key, 2:57 we just need to add the @PrimaryKey annotation before that column. 3:00 Let's add a line above id and then type, @PrimaryKey. 3:04 You may need to use Alt+Enter to import it. 3:14 Awesome, that's it for our Pizza entity. 3:17 Now let's update the Topping class. 3:20 Let's add the @ entity annotation, and then the @ primary key annotation. 3:24 You could also put it on the same line as the id if you prefer. 3:32 Now that we've got Pizza and Topping entities, 3:37 it's time to create the PizzaTopping entity, which we'll do in the next video. 3:40