Question

正如我之前所说的那样，我非常喜欢android，现在我遇到了一个非常令人不安的问题。我有一个数据库，我需要在表中添加一个新字段。我不太了解android和java .. 所以请大家，一点帮助将不胜感激...... 这是我的数据库代码：

public class MySQLiteHelper extends SQLiteOpenHelper {

  public static final String TABLE_COMMENTS = "comments";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_COMMENT = "comment";

  private static final String DATABASE_NAME = "commments.db";
  private static final int DATABASE_VERSION = 1;

  // Database creation sql statement
  private static final String DATABASE_CREATE = "create table "
      + TABLE_COMMENTS + "(" + COLUMN_ID
      + " integer primary key autoincrement, " + COLUMN_COMMENT
      + " text not null);";

  public MySQLiteHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w(MySQLiteHelper.class.getName(),
        "Upgrading database from version " + oldVersion + " to "
            + newVersion + ", which will destroy all old data");
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_COMMENTS);
    onCreate(db);
  }

}

这是针对数据库的功能：

    public class CommentsDataSource {

  // Database fields
  private SQLiteDatabase database;
  private MySQLiteHelper dbHelper;
  private String[] allColumns = { MySQLiteHelper.COLUMN_ID,
      MySQLiteHelper.COLUMN_COMMENT };

  public CommentsDataSource(Context context) {
    dbHelper = new MySQLiteHelper(context);
  }

  public void open() throws SQLException {
    database = dbHelper.getWritableDatabase();
  }

  public void close() {
    dbHelper.close();
  }

  public Comment createComment(String comment) {
    ContentValues values = new ContentValues();
    values.put(MySQLiteHelper.COLUMN_COMMENT, comment);
    long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
        values);
    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
        allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
        null, null, null);
    cursor.moveToFirst();
    Comment newComment = cursorToComment(cursor);
    cursor.close();
    return newComment;
  }

  public void deleteComment(Comment comment) {
    long id = comment.getId();
    System.out.println("Comment deleted with id: " + id);
    database.delete(MySQLiteHelper.TABLE_COMMENTS, MySQLiteHelper.COLUMN_ID
        + " = " + id, null);
  }

  public List<Comment> getAllComments() {
    List<Comment> comments = new ArrayList<Comment>();

    Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
        allColumns, null, null, null, null, null);

    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
      Comment comment = cursorToComment(cursor);
      comments.add(comment);
      cursor.moveToNext();
    }
    // Make sure to close the cursor
    cursor.close();
    return comments;
  }

  private Comment cursorToComment(Cursor cursor) {
    Comment comment = new Comment();
    comment.setId(cursor.getLong(0));
    comment.setComment(cursor.getString(1));
    return comment;
  }
}

这是上面课程使用的另一个类：

public class Comment {
  private long id;
  private String comment;

  public long getId() {
    return id;
  }

  public void setId(long id) {
    this.id = id;
  }

  public String getComment() {
    return comment;
  }

  public void setComment(String comment) {
    this.comment = comment;
  }

  // Will be used by the ArrayAdapter in the ListView
  @Override
  public String toString() {
    return comment;
  }
}

当我只使用一个字段（即评论）时，所有这些代码都可以正常工作我想添加三个名为“Address”，“Age”，“Gender”的新字段，如果可能的话，更改数据库名称，我似乎无法以正确的方式改变它以获得我想要的东西。请告诉我所需的正确改动。请帮助我！

提前致谢，等待你的回复...

Answer 1

如果可能的话更改数据库名称，我似乎无法做到以正确的方式改变它以获得我想要的东西。请告诉我正确的需要改变。

有两种方法：

正确实施onUpgrade()类的SQLiteOpenHelper方法（如果您需要更新）
只需更新您的数据库类（修改DDL语句e.q.添加新列并更改数据库如果您愿意，可以在将更新后的应用程序安装到您的设备之前删除应用程序的数据（在设备中，它位于应用程序的设置中）经理）。这将删除连接到您的应用程序的所有数据（数据库，偏好等）

看看

Android: upgrading DB version and adding new table

Answer 2

在表格中创建新列：

String Comment_table = String.format("CREATE TABLE %s " +
                "(%s INTEGER PRIMARY KEY AUTOINCREMENT ," +
                " %s TEXT , %s TEXT , %s TEXT ," +
                " %s TEXT  )",

                Comment_Table,
                Comment_ID ,
                Comment , Address , Age ,
                Gender );

（这里，列名是静态字符串，声明为类变量）。

在android中的SQLite中添加一个新字段

2 个答案: