如何检查android sqlite中是否存在表

Question

我已经使用 sqlite 插入数据并取回结果，但我所做的是首先显示包含获取的值的列表，如果没有值，则列表显示空视图，指示用户将新项目添加到sqlite 数据库。但是当我尝试这个时，它向我显示一个错误，数据库中不存在这样的表。我想知道如何检查表是否已创建或是否有值。如果没有，如何向用户抛出异常以向表中插入新项目。

数据库：

public class BuisnessDatabaseHandler extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "receiptExample";

// Labels table name
private static final String TABLE_LABELS = "buisnesslabels";
private static final String KEY_ID = "id";
private static final String KEY_IMAGE = "image";
private static final String KEY_STATUS="status";
private static final String KEY_UPLOADSTATUS = "uplaodstatus";
private static final String KEY_USERID="userid";
SQLiteDatabase db;
public BuisnessDatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
    // Category table create query
    String CREATE_CATEGORIES_TABLE = "CREATE TABLE " + TABLE_LABELS + "("
            + KEY_ID + " INTEGER PRIMARY KEY,"
            + KEY_IMAGE + " BLOB,"
            + KEY_STATUS + " TEXT,"
            + KEY_UPLOADSTATUS + " TEXT,"
            + KEY_USERID + " TEXT" + ");";

    db.execSQL(CREATE_CATEGORIES_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_LABELS);

    // Create tables again
    onCreate(db);
}
public void insertLabel(byte[] imag,String status,String uploadstatus,String userid){
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    //values.put(KEY_ID,id);
    values.put(KEY_IMAGE,imag);
    values.put(KEY_STATUS,status);
    values.put(KEY_UPLOADSTATUS,uploadstatus);
    values.put(KEY_USERID,userid);
    // Inserting Row
    db.insert(TABLE_LABELS, null, values);
    db.close(); // Closing database connection
}
public ArrayList<BuisnesslistItems> getAllLabels(){
    //  List<String> labels = new ArrayList<String>();
    ArrayList<BuisnesslistItems>labels=new ArrayList<BuisnesslistItems>();

    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_LABELS;

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {

            BuisnesslistItems buisnesslistItems=new BuisnesslistItems();
            buisnesslistItems.setImage(cursor.getBlob(1));
            buisnesslistItems.setStatus("Status:"+cursor.getString(2));


            labels.add(buisnesslistItems);
        } while (cursor.moveToNext());
    }

    // closing connection
    cursor.close();
    db.close();

    // returning lables
    return labels;
}

public String composeJSONfromSQLite(){
    ArrayList<HashMap<String, String>> label;
    label = new ArrayList<HashMap<String, String>>();
    String selectQuery = "SELECT  * FROM labels where " + KEY_STATUS + " = '"+"no"+"'";
    SQLiteDatabase database = this.getWritableDatabase();
    Cursor cursor = database.rawQuery(selectQuery, null);
    if (cursor.moveToFirst()) {
        String encodedImage = Base64.encodeToString(cursor.getBlob(1), Base64.DEFAULT);
        do {
            HashMap<String, String> map = new HashMap<String, String>();
            map.put(KEY_ID, cursor.getString(0));
            map.put(KEY_IMAGE, encodedImage);
            map.put(KEY_USERID,cursor.getString(4));
            map.put(KEY_STATUS,"yes");
            label.add(map);
        } while (cursor.moveToNext());
    }
    database.close();
    Gson gson = new GsonBuilder().create();
    //Use GSON to serialize Array List to JSON
    return gson.toJson(label);
}

/**
 * Get Sync status of SQLite
 * @return
 */
public String getSyncStatus(){
    String msg = null;
    if(this.dbSyncCount() == 0){
        msg = "Wallet is Sync with cloud!";
    }else{
        msg = "Wallet needs to be Sync\n";
    }
    return msg;
}

/**
 * Get SQLite records that are yet to be Synced
 * @return
 */
public int dbSyncCount(){
    int count = 0;
    String selectQuery = "SELECT  * FROM labels where " +KEY_STATUS+" = '"+"no"+"'";
    SQLiteDatabase database = this.getWritableDatabase();
    Cursor cursor = database.rawQuery(selectQuery, null);
    count = cursor.getCount();
    database.close();
    return count;
}

/**
 * Update Sync status against each User ID
 * @param id
 * @param status
 */
public void updateSyncStatus(String id, String status){
    SQLiteDatabase database = this.getWritableDatabase();
    String updateQuery = "Update labels set " + KEY_STATUS + " = '"+ status +"'," + KEY_UPLOADSTATUS + " = 'Uploaded' where " + KEY_ID + "="+"'"+ id +"'";
    Log.d("query", updateQuery);
    database.execSQL(updateQuery);
    database.close();
}
public void deleteUploaded(String status){
    SQLiteDatabase database=this.getWritableDatabase();
    String deleteQuery="Delete From labels where " + KEY_STATUS+ " = 'yes' ";
    Log.d("dquery",deleteQuery);
    database.execSQL(deleteQuery);
    database.close();
}

列表页：

BuisnessDatabaseHandler db = new BuisnessDatabaseHandler(getApplicationContext());

    // Spinner Drop down elements
    //  List<String> lables = db.getAllLabels();
    ArrayList<BuisnesslistItems>list=new ArrayList<BuisnesslistItems>();
    list=db.getAllLabels();
    buisnessListAdapter = new BuisnessListAdapter(
            BuisnessList.this, list);
    if (loginSession.isLoggedIn()) {
        loginSession.checkLogin();
        listView.setAdapter(buisnessListAdapter);
        listView.setEmptyView(findViewById(R.id.empty));

        Toast.makeText(getApplicationContext(), db.getSyncStatus(), Toast.LENGTH_LONG).show();
    }else{
        Intent i=new Intent(BuisnessList.this,LoginPAge.class);
        startActivity(i);
        BuisnessList.this.finish();
    }

错误：

 Caused by: android.database.sqlite.SQLiteException: no such table: buisnesslabels (code 1): , while compiling: SELECT  * FROM buisnesslabels
        at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
        at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:898)
        at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:509)
        at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
        at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
        at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
        at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
        at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1346)
        at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1285)
        at nidhinkumar.reccs.buisnesscarddetails.BuisnessDatabaseHandler.getAllLabels(BuisnessDatabaseHandler.java:81)
        at nidhinkumar.reccs.buisnesscarddetails.BuisnessList.syncSQLiteMySQLDB(BuisnessList.java:364)
        at nidhinkumar.reccs.buisnesscarddetails.BuisnessList.init(BuisnessList.java:216)
        at nidhinkumar.reccs.buisnesscarddetails.BuisnessList.onCreate(BuisnessList.java:143)

我想在列表页面中添加一个条件来检查表是否存在以及它是否有值

Answer 1

您可以使用以下语句来检查表是否存在：

Cursor cursor = db.rawQuery("select DISTINCT tbl_name from sqlite_master where tbl_name = '"
    + TABLE_NAME + "'", null);

SQLite 维护一个名为sqlite_master的表，其中包含数据库中所有表的信息。因此，如果结果游标返回的计数为 1，您就知道该表存在。检查后，使用所需的查询再次查询数据库：

cursor = your-query-here; 

并cursor.getCount();再次使用以确定您是否有数据。如果cursor.getCount();返回大于 0，那么您就有了想要的数据。