将会议室数据库中的唯一约束添加到多列 [英] add unique constraint in room database to multiple column
问题描述
我在房间里只有一个实体
I have one entity in room
@Entity(foreignKeys ={
@ForeignKey(entity = Label.class, parentColumns = "_id", childColumns = "labelId", onDelete = CASCADE),
@ForeignKey(entity = Task.class, parentColumns = "_id", childColumns = "taskId", onDelete = CASCADE)
})
public class LabelOfTask extends Data{
@ColumnInfo(name = "labelId")
private Integer labelId;
@ColumnInfo(name = "taskId")
private Integer taskId;
}
该实体的
sql语法如下
sql syntax of this entity is as below
CREATE TABLE `LabelOfTask` (
`_id` INTEGER PRIMARY KEY AUTOINCREMENT,
`labelId` INTEGER,
`taskId` INTEGER,
FOREIGN KEY(`labelId`) REFERENCES `Label`(`_id`) ON UPDATE NO ACTION ON DELETE CASCADE ,
FOREIGN KEY(`taskId`) REFERENCES `Task`(`_id`) ON UPDATE NO ACTION ON DELETE CASCADE
);
但是如果要将以下约束附加到表的自动生成的sql模式,我需要在实体类中添加哪些更改或注释
but what change or annotation I need to add in entity class if I want to append below constraint to the auto generated sql schema of the table
unique (labelId, taskId)
最终,我想使用房间库在一个表(或房间的实体)中使labelId和taskId的组合唯一.
Ultimately I want to make combination of labelId and taskId unique in a table(or entity of room) using room library.
推荐答案
不支持对列的普通UNIQUE约束,而不是通过索引.
您可以通过将@Index批注的unique属性设置为true来强制执行此uniqueness属性.下面的代码示例(Java)防止表具有两行,其中两行的firstName和lastName列包含一组相同的值:
You can enforce this uniqueness property by setting the unique property of an @Index annotation to true. The following code sample (Java) prevents a table from having two rows that contain the same set of values for the firstName and lastName columns:
@Entity(indices = {@Index(value = {"first_name", "last_name"},
unique = true)})
class User {
@PrimaryKey
public int id;
@ColumnInfo(name = "first_name")
public String firstName;
@ColumnInfo(name = "last_name")
public String lastName;
@Ignore
Bitmap picture;
}
注释的Kotlin等效项如下:
The Kotlin equivalent of the annotation is given below:
@Entity(indices = arrayOf(Index(value = ["first_name", "last_name"], unique = true)))
在您的代码中,您可以进行以下更改以具有唯一约束
In your code you can do the following changes to have UNIQUE constraints
@Entity(foreignKeys ={
@ForeignKey(entity = Label.class, parentColumns = "_id", childColumns = "labelId", onDelete = CASCADE),
@ForeignKey(entity = Task.class, parentColumns = "_id", childColumns = "taskId", onDelete = CASCADE)},
indices = {@Index(value = {"labelId", "taskId"},
unique = true)}
)
public class LabelOfTask extends Data{
@ColumnInfo(name = "labelId")
private Integer labelId;
@ColumnInfo(name = "taskId")
private Integer taskId;
}
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