如何将新列添加到Android SQLite数据库？

Question

我有Android SQLite数据库的一个问题.

我有一个表包含一个field.StudentFname和该应用程序与Android 2.3.1正常工作,现在如果我添加另一个字段,那么我的应用程序无法正常工作.

任何人都可以帮助我了解数据库的人,

Answer 1

你可以ALTER TABLE在你的onUpgrade()方法上使用函数,如下所示:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  // If you need to add a column
  if (newVersion > oldVersion) {
     db.execSQL("ALTER TABLE foo ADD COLUMN new_column INTEGER DEFAULT 0");
  }
}

显然,SQLite将根据列定义而有所不同.

Answer 2

我在自己的应用程序上需要帮助时遇到了这个帖子,但是看到了很多答案的问题.我建议你做以下事情:

private static final String DATABASE_ALTER_TEAM_1 = "ALTER TABLE "
    + TABLE_TEAM + " ADD COLUMN " + COLUMN_COACH + " string;";

private static final String DATABASE_ALTER_TEAM_2 = "ALTER TABLE "
    + TABLE_TEAM + " ADD COLUMN " + COLUMN_STADIUM + " string;";

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (oldVersion < 2) {
         db.execSQL(DATABASE_ALTER_TEAM_1);
    }
    if (oldVersion < 3) {
         db.execSQL(DATABASE_ALTER_TEAM_2);
    }
}

您希望确保在用户升级多个版本时代码将起作用,并且update语句仅运行所需的一次升级.有关这方面的更多信息,请查看此博客.

Answer 3

最简单的方法是SQL to the onUpgrade()在你的方法中添加一些方法SQLiteOpenHelper class.就像是:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    // If you need to add a new column
    if (newVersion > oldVersion) {
        db.execSQL("ALTER TABLE student ADD COLUMN student_rollno INTEGER DEFAULT 0");
    }
}

Answer 4

也许使用switch而不是if/then会稍微优雅的方法将从任何架构升级到最新的架构......

这里也是改变表格语法的一个不错的页面:http://alvinalexander.com/android/sqlite-alter-table-syntax-examples

public static final String TABLE_TEAM = "team";
public static final String COLUMN_COACH = "coach";
public static final String COLUMN_STADIUM = "stadium";


private static final String DATABASE_ALTER_TEAM_TO_V2 = "ALTER TABLE "
    + TABLE_TEAM + " ADD COLUMN " + COLUMN_COACH + " TEXT;";

private static final String DATABASE_ALTER_TEAM_TO_V3 = "ALTER TABLE "
    + TABLE_TEAM + " ADD COLUMN " + COLUMN_STADIUM + " TEXT;";


@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    switch (oldVersion)
    {
        case 1:
            //upgrade from version 1 to 2
            db.execSQL(DATABASE_ALTER_TEAM_TO_V2);
        case 2:
            //upgrade from version 2 to 3
            db.execSQL(DATABASE_ALTER_TEAM_TO_V3);

        //and so on.. do not add breaks so that switch will
        //start at oldVersion, and run straight through to the latest

    }

}

Answer 5

我已经完成了以下方法，它已为我解决

如果数据库版本：6

Ex : There is a table with 5 columns

当您升级到：7（我在 3 个表中添加 1 个新列）

 1. We need to add the columns when creating a table

 2. onUpgrade method:

 if (oldVersion < 7) 
 { 
    db.execSQL(DATABASE_ALTER_ADD_PAPER_PAID);
    db.execSQL(DATABASE_ALTER_LAST_UPLOADED);
    db.execSQL(DATABASE_ALTER_PAPER_LABEL); 
 }

其中：“DATABASE_ALTER_ADD_PAPER_PAID”是查询。

EX: public static final String DATABASE_ALTER_ADD_PAPER_PAID = "ALTER TABLE "
                + TableConstants.MY_PAPERS_TABLE + " ADD COLUMN " + COLUMN_PAPER_PAID + " TEXT;";

经过以上两个操作后，对于全新安装用户和应用程序升级用户来说就可以正常工作了