Question

我对使用SQL存储Android数据项不太熟悉，但是在下面，我有几种方法可以插入新数据项并打印所有现有数据。

我的Flight类具有以下属性：

航班号-字符串
航空公司-字符串
日期-字符串
图像路径-字符串
reg-字符串
类型-字符串ID
int（每个实例唯一）

由于某种原因，我无法打印数据，因此不确定insertFlight()方法或databaseToString()方法是否存在问题。

public class DatabaseSQ extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "FlightDatabase.db";
    public static final String TABLE_FLIGHTS = "flights";
    private static final int DATABASE_VERSION = 1;
    public static final String FLIGHT_COLUMN_ID = "_id";
    public static final String FLIGHT_NUMBER = "number";
    public static final String FLIGHT_DATE = "date";
    public static final String FLIGHT_REG = "reg";
    public static final String FLIGHT_AIRLINE = "airline";
    public static final String FLIGHT_TYPE = "type";
    public static final String FLIGHT_IMAGE_PATH = "image";

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


    @Override
    public void onCreate(SQLiteDatabase db) {

        String query = "CREATE TABLE " + TABLE_FLIGHTS + "(" +
            FLIGHT_COLUMN_ID + "INTEGER PRIMARY KEY, " +
                FLIGHT_NUMBER + " TEXT, " +
                FLIGHT_DATE + " TEXT, " +
                FLIGHT_REG + " TEXT, " +
                FLIGHT_AIRLINE + " TEXT, " +
                FLIGHT_TYPE + " TEXT, " +
                FLIGHT_IMAGE_PATH + " TEXT " +
                ");";

        db.execSQL(query);


    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_FLIGHTS);
        onCreate(db);
    }

    public void insertFlight(Flight toADD) {

        ContentValues contentValues = new ContentValues();

        contentValues.put(FLIGHT_COLUMN_ID, toADD.getId());
        contentValues.put(FLIGHT_NUMBER, toADD.getFlightNumber());
        contentValues.put(FLIGHT_DATE, toADD.getDate());
        contentValues.put(FLIGHT_REG, toADD.getReg());
        contentValues.put(FLIGHT_AIRLINE, toADD.getAirline());
        contentValues.put(FLIGHT_TYPE, toADD.getType());
        contentValues.put(FLIGHT_IMAGE_PATH, toADD.getImagePath());

        SQLiteDatabase db = getWritableDatabase();




        db.insert(TABLE_FLIGHTS, null, contentValues);
        db.close();

    }

    public String databaseToString() {

        String dbString = "";
        SQLiteDatabase db = getWritableDatabase();
        String query = "SELECT * FROM " + TABLE_FLIGHTS + " WHERE 1";

        Cursor c = db.rawQuery(query, null);
        c.moveToFirst();

        while(!c.isAfterLast()) {
            if(c.getString(c.getColumnIndex("number")) != null) {
                dbString += c.getString(c.getColumnIndex("number"));
                dbString += "\n";
            }
            c.moveToNext();
        }
        db.close();
        return dbString;
    }
}

在另一个活动文件中，单击一个按钮时，将调用此数据库，必须存储一个新的飞行对象并将其飞行号传递给主活动。（数据库对象dbHandler之前已实例化。）

public void AddFlight(View view) {

        String name = nameText.getText().toString();
        String date = dateText.getText().toString();
        String airline = airlineText.getText().toString();
        String type = typeText.getText().toString();
        String reg = regText.getText().toString();


        Context context = this;
        Class destination = MainActivity.class;

        Intent goBackToMain = new Intent(context, destination);


        Flight newFlight = new Flight(name, date, reg, airline, type, mCurrentPhotoPath);

        dbHandler.insertFlight(newFlight);

        String data = dbHandler.databaseToString();
        goBackToMain.putExtra(Intent.EXTRA_TEXT, data);

        startActivity(goBackToMain);
    }

Answer 1

问题是因为您在表上错误地移动了光标。请按照以下步骤尝试

Cursor c = db.rawQuery(query, null);
if(c != null) {
    while(c.moveToNext()) {
        dbString += c.getString(c.getColumnIndex("number"));
        dbString += "\n";
    }
    c.close()
}

Answer 2

FLIGHT_COLUMN_ID + "INTEGER PRIMARY KEY, " +

您在列名称及其类型之间缺少空格。那本身不是语法错误，列名变为_idINTEGER。

contentValues.put(FLIGHT_COLUMN_ID, toADD.getId());

...

db.insert(TABLE_FLIGHTS, null, contentValues);

由于没有FLIGHT_COLUMN_ID列，因此此插入将失败。使用insertOrThrow()而非insert()引发错误错误。

此外，您无需在INTEGER PRIMARY KEY列中插入值-将会自动为您生成一个新的rowid。

更正CREATE TABLE SQL之后，您可以卸载应用程序以使onCreate()重新运行。

使用SQLite存储数据

2 个答案: