[android] How to make primary key as autoincrement for Room Persistence lib

I am creating an Entity (Room Persistence Library) class Food, where I want to make foodId as autoincrement.

@Entity
class Food(var foodName: String, var foodDesc: String, var protein: Double, var carbs: Double, var fat: Double)
{
    @PrimaryKey
    var foodId: Int = 0
    var calories: Double = 0.toDouble()
}

How can I set foodId an autoincrement field?

Its unbelievable after so many answers, but I did it little differently in the end. I don't like primary key to be nullable, I want to have it as first argument and also want to insert without defining it and also it should not be var.

@Entity(tableName = "employments")
data class Employment(
    @PrimaryKey(autoGenerate = true) val id: Long,
    @ColumnInfo(name = "code") val code: String,
    @ColumnInfo(name = "title") val name: String
){
    constructor(code: String, name: String) : this(0, code, name)
}

This works for me:

@Entity(tableName = "note_table")
data class Note(
    @ColumnInfo(name="title") var title: String,
    @ColumnInfo(name="description") var description: String = "",
    @ColumnInfo(name="priority") var priority: Int,
    @PrimaryKey(autoGenerate = true) var id: Int = 0//last so that we don't have to pass an ID value or named arguments
)

Note that the id is last to avoid having to use named arguments when creating the entity, before inserting it into Room. Once it's been added to room, use the id when updating the entity.

@Entity(tableName = "user")
data class User(

@PrimaryKey(autoGenerate = true)  var id: Int?,
       var name: String,
       var dob: String,
       var address: String,
       var gender: String
)
{
    constructor():this(null,
        "","","","")
}

You can add @PrimaryKey(autoGenerate = true) like this:

@Entity
data class Food(
        var foodName: String, 
        var foodDesc: String, 
        var protein: Double, 
        var carbs: Double, 
        var fat: Double
){
    @PrimaryKey(autoGenerate = true)
    var foodId: Int = 0 // or foodId: Int? = null
    var calories: Double = 0.toDouble()
}

add @PrimaryKey(autoGenerate = true)

@Entity
public class User {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "full_name")
    private String name;

    @ColumnInfo(name = "phone")
    private String phone;

    public User(){
    }

    //type-1
    public User(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }

    //type-2
    public User(int id, String name, String phone) {
        this.id = id;
        this.name = name;
        this.phone = phone;
    }

}

while storing data

 //type-1
 db.userDao().InsertAll(new User(sName,sPhone)); 

 //type-2
 db.userDao().InsertAll(new User(0,sName,sPhone)); 

type-1

If you are not passing value for primary key, by default it will 0 or null.

type-2

Put null or zero for the id while creating object (my case user object)

If the field type is long or int (or its TypeConverter converts it to a long or int), Insert methods treat 0 as not-set while inserting the item.

If the field's type is Integer or Long (Object) (or its TypeConverter converts it to an Integer or a Long), Insert methods treat null as not-set while inserting the item.

Annotate your Entity class with the code below.

In Java:

@PrimaryKey(autoGenerate = true)
private int id;

In Kotlin:

@PrimaryKey(autoGenerate = true)
var id: Int

Room will then auto-generate and auto-increment the id field.

For example, if you have a users entity you want to store, with fields (firstname, lastname , email) and you want autogenerated id, you do this.

@Entity(tableName = "users")
data class Users(
   @PrimaryKey(autoGenerate = true)
   val id: Long,
   val firstname: String,
   val lastname: String,
   val email: String
)

Room will then autogenerate and auto-increment the id field.