android sqlite定义查询

Question

大家好 我有一个名为 books 的表，它有 4 列（标题、作者、isbn、年份）我使用此查询来调用以检查是否有相同的 isbn我正在尝试插入

Cursor c =db.query ("books", "isbn", 12344556 , null, null, null, null);

示例：isbn 我正在搜索 = 12344556

并且我也收到此错误：

The method query(String, String, String, null, null, null, null) is undefined for the type DBAdapter

请提供一些帮助......???我该如何解决这个问题我不知道如何定义方法查询....!!

这是我想学习的例子......

http://www.android10.org/index.php/articlesdatastorage/235-creating-and-using-databases-in-android-one

这是DBAdapter.java

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter 
{
    public static final String KEY_ROWID = "_id";
    public static final String KEY_ISBN = "isbn";
    public static final String KEY_TITLE = "title";
    public static final String KEY_PUBLISHER = "publisher";    
    private static final String TAG = "DBAdapter";

    private static final String DATABASE_NAME = "books";
    private static final String DATABASE_TABLE = "titles";
    private static final int DATABASE_VERSION = 1;

    private static final String DATABASE_CREATE =
        "create table titles (_id integer primary key autoincrement, "
        + "isbn text not null, title text not null, " 
        + "publisher text not null);";

    private final Context context; 

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBAdapter(Context ctx) 
    {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper 
    {
        DatabaseHelper(Context context) 
        {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

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

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

    //---opens the database---
    public DBAdapter open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    //---closes the database---    
    public void close() 
    {
        DBHelper.close();
    }

    //---insert a title into the database---
    public long insertTitle(String isbn, String title, String publisher) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_ISBN, isbn);
        initialValues.put(KEY_TITLE, title);
        initialValues.put(KEY_PUBLISHER, publisher);
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    //---deletes a particular title---
    public boolean deleteTitle(long rowId) 
    {
        return db.delete(DATABASE_TABLE, KEY_ROWID + 
                "=" + rowId, null) > 0;
    }

    //---retrieves all the titles---
    public Cursor getAllTitles() 
    {
        return db.query(DATABASE_TABLE, new String[] {
                KEY_ROWID, 
                KEY_ISBN,
                KEY_TITLE,
                KEY_PUBLISHER}, 
                null, 
                null, 
                null, 
                null, 
                null);
    }

    //---retrieves a particular title---
    public Cursor getTitle(long rowId) throws SQLException 
    {
        Cursor mCursor =
                db.query(true, DATABASE_TABLE, new String[] {
                        KEY_ROWID,
                        KEY_ISBN, 
                        KEY_TITLE,
                        KEY_PUBLISHER
                        }, 
                        KEY_ROWID + "=" + rowId, 
                        null,
                        null, 
                        null, 
                        null, 
                        null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---updates a title---
    public boolean updateTitle(long rowId, String isbn, 
    String title, String publisher) 
    {
        ContentValues args = new ContentValues();
        args.put(KEY_ISBN, isbn);
        args.put(KEY_TITLE, title);
        args.put(KEY_PUBLISHER, publisher);
        return db.update(DATABASE_TABLE, args, 
                         KEY_ROWID + "=" + rowId, null) > 0;
    }
}

Answer 1

这一行：

The method query(String, String, String, null, null, null, null) is undefined for the type DBAdapter

表明您以某种方式在 DBAdapter 对象而不是 SQLiteDatabase 对象上调用 query() （这就是我假设您想要做的）。

您发布的第一行是否与您列出的错误相对应？我对此表示怀疑，因为您的第三个参数是 int 但错误将其列为字符串。

Answer 2

我认为你想要这样的东西：

String isbn = "12344556";
Cursor c = db.query(DATABASE_NAME, new String [] { 
    KEY_ISBN
    },
    KEY_ISBN + "='" + isbn + "'",
    null,
    null,
    null,
    null);

然后你可以检查计数，如果大于 0，则你的书存在。

if (c.getCount() > 0)
    //book exists
else
    //book does not exist