我正在创建一个实体（房间持久性库）类 Food，我想在其中创建foodId自动增量。
@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()
}
如何设置foodId自动增量字段？
你可以@PrimaryKey(autoGenerate = true)这样添加：
@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.
经过这么多答案，这令人难以置信，但我最终还是做了一点不同。我不喜欢主键可以为空，我想把它作为第一个参数，也想插入而不定义它，它也不应该是 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)
}
这对我有用：
@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
)
请注意，在将实体插入到 Room 之前，id 是最后一个，以避免在创建实体时使用命名参数。将其添加到房间后，在更新实体时使用 id。
例如，如果您有一个users要存储的实体，带有字段(firstname, lastname , email)并且您想要自动生成的 id，您可以这样做。
@Entity(tableName = "users")
data class Users(
@PrimaryKey(autoGenerate = true)
val id: Long,
val firstname: String,
val lastname: String,
val email: String
)
Room 然后将自动生成并自动增加该id字段。
@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,
"","","","")
}
在下面的示例中，当您创建新用户时，按构造函数中的方式传递参数。Room 会自动生成 id。所有用户对象 id 都已在 id setter 中设置为 int 默认值，因此不要调用 setId
@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(String name, String phone) {
this.name = name;
this.phone = phone;
}
public void setId(int id){
this.id = id;
}
}
使用下面的代码注释您的 Entity 类。
在 Java 中：
@PrimaryKey(autoGenerate = true)
private int id;
在科特林：
@PrimaryKey(autoGenerate = true)
var id: Int
Room 将自动生成并自动增加 id 字段。