我已经在我的SQLiteOpenHelper onCreate()中创建了我的表
SQLiteException: no such table
or
SQLiteException: no such column
错误。为什么?
注意: (这是每周数十个类似问题的汇总。试图在这里提供一个“规范的”社区wiki问题/答案,以便所有这些问题都可以指向一个很好的参考。)
我已经在我的SQLiteOpenHelper onCreate()中创建了我的表
SQLiteException: no such table
or
SQLiteException: no such column
错误。为什么?
注意: (这是每周数十个类似问题的汇总。试图在这里提供一个“规范的”社区wiki问题/答案,以便所有这些问题都可以指向一个很好的参考。)
当前回答
您可以创建数据库和表
public class DbHelper extends SQLiteOpenHelper {
private static final String DBNAME = "testdatbase.db";
private static final int VERSION = 1;
public DbHelper(Context context) {
super(context, DBNAME, null, VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("create table BookDb(id integer primary key autoincrement,BookName text,Author text,IssuedOn text,DueDate text,Fine text,Totalfine text");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS BookDb");
onCreate(db);
}
}
注意:如果您想创建另一个表或添加列或没有这样的表,只需增加VERSION
其他回答
在DatabaseHandler/DatabaseManager类中重新检查您的查询(您曾经使用过的类)
Sqliteopenhelper的方法有create方法和upgrade方法,create方法在任何表第一次创建时使用,而upgrade方法将在每次表的列数发生变化时调用。
SQLiteOpenHelper onCreate()和onUpgrade()回调在数据库实际打开时被调用,例如通过调用getWritableDatabase()。在创建数据库帮助对象本身时,不会打开数据库。
SQLiteOpenHelper数据库文件的版本。版本号是传递给构造函数的int参数。在数据库文件中,版本号存储在PRAGMA user_version中。
onCreate()仅在数据库文件不存在且刚刚创建时运行。如果onCreate()成功返回(不抛出异常),则假定数据库是使用所请求的版本号创建的。作为暗示,你不应该自己在onCreate()中捕获SQLExceptions。
onUpgrade()仅在数据库文件存在但存储的版本号低于构造函数中请求的版本号时调用。onUpgrade()应该将表模式更新到请求的版本。
当在代码(onCreate())中更改表模式时,应该确保数据库已更新。两种主要方法:
Delete the old database file so that onCreate() is run again. This is often preferred at development time where you have control over the installed versions and data loss is not an issue. Some ways to delete the database file: Uninstall the application. Use the application manager or adb uninstall your.package.name from the shell. Clear application data. Use the application manager. Increment the database version so that onUpgrade() is invoked. This is slightly more complicated as more code is needed. For development time schema upgrades where data loss is not an issue, you can just use execSQL("DROP TABLE IF EXISTS <tablename>") in to remove your existing tables and call onCreate() to recreate the database. For released versions, you should implement data migration in onUpgrade() so your users don't lose their data.
onCreate ()
When we create DataBase at a first time (i.e Database is not exists) onCreate() create database with version which is passed in SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) onCreate() method is creating the tables you’ve defined and executing any other code you’ve written. However, this method will only be called if the SQLite file is missing in your app’s data directory (/data/data/your.apps.classpath/databases). This method will not be called if you’ve changed your code and relaunched in the emulator. If you want onCreate() to run you need to use adb to delete the SQLite database file.
onUpgrade()
SQLiteOpenHelper应该调用超级构造函数。 onUpgrade()方法只会在版本整数大于应用程序中运行的当前版本时被调用。 如果希望调用onUpgrade()方法,则需要增加代码中的版本号。
从模拟器或设备卸载应用程序。再次运行应用程序。(OnCreate()不执行时,数据库已经存在)