Saving Data on Android

7
Chapter 7: Mastering 
Rela/ons
By Aldo Olivares
In the previous chapter, you learned all you need to know about tables, entities and 
annotations. You also learned how to create your database and how to get a runtime 
instance of it by using the 
Room.databaseBuilder
 method.
In this chapter, you are going to learn even more about entities by creating relations 
between them using foreign keys and the 
@Relation
 annotation. Along the way, you 
will learn:
• How to create a relationship using primary keys and foreign keys.
• How to define a one to many relationship in Room.
• How to represent different kinds of relationships using entity-relationship 
diagrams.
• How to use the 
@Embedded
 annotation.
• How to use the 
@ForeignKey
 annotation.
• How to use the 
@Relationship
 annotation.
Ready? Let's get started.
Note:
 This chapter assumes you have basic knowledge of Kotlin and Android. 
If you’re new to Android, check out our 
Android tutorials
. If you know 
Android, but are unfamiliar with Kotlin, take a look at 
Kotlin For Android: An 
Introduction
.
raywenderlich.com
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GeTng started
If you are following along with your own app, open it up. If not, don't worry you can 
use the starter project for this chapter, which you can find in the attachments. Now, 
open the app in Android Studio 3.2 or greater by going to