创建视图并将其关联到数据库
使用集合让一切井井有条
根据您的偏好保存内容并对其进行分类。
2.1.0 及更高版本的 Room 持久性库 为 SQLite 数据库视图 提供了支持,从而允许您将查询封装到类中。Room 将这些查询支持的类称为视图,在 DAO 中使用时,它们的行为与简单数据对象的行为相同。
注意 :与实体 类似,您可以针对视图运行 SELECT
语句。不过,您无法针对视图运行 INSERT
、UPDATE
或 DELETE
语句。 创建视图
如需创建视图,请将 @DatabaseView
注释添加到类中。将注释的值设为类应该表示的查询。
以下代码段提供了一个视图示例:
Kotlin
@DatabaseView("SELECT user.id, user.name, user.departmentId," +
"department.name AS departmentName FROM user " +
"INNER JOIN department ON user.departmentId = department.id")
data class UserDetail(
val id: Long,
val name: String?,
val departmentId: Long,
val departmentName: String?
)
Java
@DatabaseView("SELECT user.id, user.name, user.departmentId," +
"department.name AS departmentName FROM user " +
"INNER JOIN department ON user.departmentId = department.id")
public class UserDetail {
public long id;
public String name;
public long departmentId;
public String departmentName;
}
将视图与数据库相关联
如需将此视图添加为应用数据库的一部分,请在应用的 @Database
注释中添加 views
属性:
Kotlin
@Database(entities = [User::class],
views =[UserDetail::class] , version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
}
Java
@Database(entities = {User.class}, views = {UserDetail.class} ,
version = 1)
public abstract class AppDatabase extends RoomDatabase {
public abstract UserDao userDao();
}
本页面上的内容和代码示例受内容许可 部分所述许可的限制。Java 和 OpenJDK 是 Oracle 和/或其关联公司的注册商标。
最后更新时间 (UTC):2024-08-29。
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"type": "thumb-down",
"id": "missingTheInformationINeed",
"label":"没有我需要的信息"
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"label":"太复杂/步骤太多"
},{
"type": "thumb-down",
"id": "outOfDate",
"label":"内容需要更新"
},{
"type": "thumb-down",
"id": "translationIssue",
"label":"翻译问题"
},{
"type": "thumb-down",
"id": "samplesCodeIssue",
"label":"示例/代码问题"
},{
"type": "thumb-down",
"id": "otherDown",
"label":"其他"
}]
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"type": "thumb-up",
"id": "easyToUnderstand",
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},{
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"id": "solvedMyProblem",
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},{
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}]
{"lastModified": "\u6700\u540e\u66f4\u65b0\u65f6\u95f4 (UTC)\uff1a2024-08-29\u3002"}
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