将房间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

我房间里有一个实体

@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
 );

但是如果我想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什么更改或注释

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使 labelId 和 taskId 的组合在表(或房间实体)中唯一.

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(通过索引除外).

您可以通过将 @Index 注释的唯一属性设置为 true 来强制执行此唯一性属性.以下代码示例 (Java) 可防止表中的两行包含 firstName 和 lastName 列的相同值集:

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;
}

Kotlin 等价的注解如下:

The Kotlin equivalent of the annotation is given below:

@Entity(indices = [Index(value = ["first_name", "last_name"], unique = true)])

在您的代码中，您可以进行以下更改以获得 UNIQUE 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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