Saving Data on Android

En//es
To create a table using Room you need to create an 
entity
, just like you did above. 
Entities in Room are defined by using a series of different 
annotations
 on classes. 
The following are the most common annotations that you will use when defining an 
entity:
@En/ty
The 
@Entity
 annotation declares that the annotated class is a Room entity. For each 
entity, a table is created in the associated SQLite database to save your data. To add 
the annotation, simply use the following approach:
@Entity
 
data
 
class
 
Movie
( 
    
//...
 
)
The above code would create a 
Movie
 table in your database. By default, Room 
always uses the name of your class as the table name, but you can use the 
tableName
  
property of the 
@Entity
 annotation to set a different name like shown below:
@Entity(tableName = "movies")
 
data
 
class
 
Movie
( 
    
//...
 
)
Now that the class is declared as an entity, you can use it in Room's setup, which 
you'll see in a bit.
Saving Data on Android
Chapter 6: Entity Definitions
raywenderlich.com
108

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@PrimaryKey
The 
@PrimaryKey
 annotation allows you to define a primary key for your table. It is 
very important to remember that each entity in Room 
must have
 at least one field 
defined as primary key:
@Entity
 
data
 
class
 
Movie
( 
    
@PrimaryKey
 
var
 id: 
Int
, 
    
var
 title: String?, 
    
var
 description: String?, 
    
var
 releaseDate: String?, 
    
var
 rating: 
Float
 
)
You can also let Room generate the primary keys automatically for you, using the 
autogenerate
 property of the 
@PrimaryKey
 annotation:
@Entity
 
data
 
class
 
Movie
( 
    
@PrimaryKey(autogenerate = true)
 
var
 id: 
Int
, 
    
var
 title: String?, 
    
var
 description: String?, 
    
var
 releaseDate: String?, 
    
var
 rating: 
Float
 
)
In the above code, the id is the primary key for your Movie table, and it is going to be 
automatically generated by Room incrementing the value each time by one 
(1,2,3,4,5,...). It is important to remember that if you set 
autogenerate
 to 
true
, the 
type affinity for the field must be