Android 数据库

class DatabaseHelper(context: Context) : SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION) {
    companion object {
        private const val DATABASE_NAME = "app.db"
        private const val DATABASE_VERSION = 1
    }
 
    override fun onCreate(db: SQLiteDatabase) {
        db.execSQL("""
            CREATE TABLE users (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                name TEXT NOT NULL,
                email TEXT UNIQUE
            )
        """)
    }
 
    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        // 数据库升级逻辑
    }
}

// 复杂关系映射
@Entity(tableName = "books")
data class Book(
    @PrimaryKey val id: Long,
    val title: String,
    val authorId: Long
)
 
@Entity(tableName = "authors")
data class Author(
    @PrimaryKey val id: Long,
    val name: String
)
 
data class BookWithAuthor(
    @Embedded val book: Book,
    @Relation(
        parentColumn = "authorId",
        entityColumn = "id"
    )
    val author: Author
)
 
// DAO接口
@Dao
interface BookDao {
    @Transaction
    @Query("SELECT * FROM books")
    suspend fun getBooksWithAuthors(): List<BookWithAuthor>
 
    @Query("SELECT * FROM books WHERE authorId = :authorId")
    fun getBooksByAuthor(authorId: Long): Flow<List<Book>>
 
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertBooks(vararg books: Book)
}