Question

我在Android中创建了一个简单的数据库。但现在我遇到了问题。我尝试了很多次，但没有解决这个问题。问题是当我想要插入新记录时，如果此记录已经输入或已经存在，那么它应该向我显示该记录已经存在的祝酒词。 DataBase class.java：

  public class DatabaseOperation extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "Student.db";
public static final String TABLE_NAME = "student_table";
public static final String COL_1 = "ID";
public static final String COL_2 = "NAME";
public static final String COL_3 = "PASS";
public static final String COL_4 = "CONTACT";
public static final String COL_5 = "NIC";
public static final String COL_6= "CONFIRM";

public DatabaseOperation(Context context) {
    super(context, DATABASE_NAME, null, 1);

}

   @Override
  public void onCreate(SQLiteDatabase db) {
    db.execSQL("create table " + TABLE_NAME +" (ID INTEGER PRIMARY KEY 
      AUTOINCREMENT,NAME TEXT,PASS TEXT,CONFIRM TEXT,NIC INTEGER,CONTACT
        INTEGER)");}     


   @Override
   public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
    db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
    onCreate(db);
   }
  public  boolean insertData(String name,String pass,String confrim,String
               contact,String nic)   
       {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues cv=new ContentValues();
    cv.put(COL_2,name);
    cv.put(COL_3,pass);
    cv.put(COL_6,confrim);
    cv.put(COL_4,contact);
    cv.put(COL_5,nic);
   long result= db.insert(TABLE_NAME,null,cv);
    if(result==-1)
        return false;
    else
        return true;

  }
  public Cursor getAllData()
  {
    SQLiteDatabase db=this.getWritableDatabase();
    Cursor res=db.rawQuery("select * from "+TABLE_NAME,null);
    return res;
}
public boolean updateData(String id,String name,String pass,String
    confrim,String contact,String nic) 
{
  SQLiteDatabase db=this.getWritableDatabase();
    ContentValues cv=new ContentValues();
    cv.put(COL_1,id);
    cv.put(COL_2,name);
    cv.put(COL_3,pass);
    cv.put(COL_6,confrim);
    cv.put(COL_4,contact);
    cv.put(COL_5,nic);
    db.update(TABLE_NAME,cv, "ID= ?",new String[]{id});
    return  true;

}
public Integer deletData(String id)
{
    SQLiteDatabase db=this.getWritableDatabase();
  return  db.delete(TABLE_NAME, "ID = ?",new String[] {id});
}

 }

这是我的注册课程

        registr.setOnClickListener(new View.OnClickListener() {
        @Override
          public void onClick(View view) {



            boolean isInserted = myDb.insertData(name.getText().toString(), pass.getText().toString(),
                    confirm.getText().toString(), cont.getText().toString(), nic.getText().toString());


            if (isInserted == true)
                Toast.makeText(getBaseContext(), "INSERTED", Toast.LENGTH_SHORT).show();
            else
                Toast.makeText(getBaseContext(), "not inserted", Toast.LENGTH_SHORT).show();



          }
       });
          next.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            linearLayout.setVisibility(View.INVISIBLE);
        }
       });
          load.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Cursor res= myDb.getAllData();
            if(res.getCount()==0)
            {
                showMessage("error","no data found");
                //Toast.makeText(getBaseContext(),"NO daTA found",Toast.LENGTH_SHORT).show();

            }
            StringBuffer buffer=new StringBuffer();
            while(res.moveToNext())
            {
                buffer.append("id:"+res.getString(0)+"\n");
                buffer.append("name:"+res.getString(1)+"\n");
                buffer.append("nic:"+res.getString(4)+"\n");
                buffer.append("contact:"+res.getString(5)+"\n\n");
            }
            showMessage("DATA",buffer.toString());

           }
         });
           update.setOnClickListener(new View.OnClickListener() {
           @Override
             public void onClick(View view) {
            boolean isUpdated=myDb.updateData(id.getText().toString(),name.getText().toString(),pass.getText().toString(),confirm.getText().toString(),
                    cont.getText().toString(),nic.getText().toString());

            if(isUpdated==true)

                Toast.makeText(getBaseContext(),"updated",Toast.LENGTH_SHORT).show();

            else
                Toast.makeText(getBaseContext(),"not updated",Toast.LENGTH_SHORT).show();

        }
        });
         delet.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Integer deletedRows=myDb.deletData(id.getText().toString());
            if(deletedRows > 0)
                Toast.makeText(getBaseContext(),"data
        deleted",Toast.LENGTH_SHORT).show();  
            else
                Toast.makeText(getBaseContext(),"not
  deleted",Toast.LENGTH_SHORT).show();
        }
        });


        }
        public void showMessage(String title,String message)
      {
    AlertDialog.Builder builder=new AlertDialog.Builder(this);
    builder.setCancelable(true);
    builder.setTitle(title);
    builder.setMessage(message);
    builder.show();
     }

    }

Answer 1

以下一段代码（方法）对于可理解的参数非常方便，请尝试检查某些记录是否已存在... 当记录已存在于您的数据库中时，以下方法将返回true。必须在您的班级 DatabaseOperations

中声明此方法

public boolean checkIfRecordExist(String nameOfTable,String columnName,String columnValue)
    {
        try
        { 
            objDatabase=this.getReadableDatabase();
            Cursor cursor=objDatabase.rawQuery("SELECT "+columnName+" FROM "+nameOfTable+" WHERE "+columnName+"='"+columnValue+"'",null);
            if (cursor.moveToFirst())
            {
                objDatabase.close();
                Log.d("Record  Already Exists", "Table is:"+nameOfTable+" ColumnName:"+columnName);
                return true;//record Exists

            }
            Log.d("New Record  ", "Table is:"+nameOfTable+" ColumnName:"+columnName+" Column Value:"+columnValue);
            objDatabase.close();        
        }
        catch(Exception errorException)
        {
            Log.d("Exception occured", "Exception occured "+errorException);
            objDatabase.close();
        }
        return false;
    }

并在您的活动中将其称为

boolean recordExists= mydb.checkIfRecordExist(DatabaseOperations.TABLE_NAME ,DatabaseOperations.COL_1 ,valueToBeChecked)
if(recordExists)
{
    //do your stuff
}

Answer 2

在Register按钮内调用此方法OnClickListener - 验证输入的名称和密码已存在于数据库中。

     /**
 * Used to check name and password is already in db.
 *
 * @param name
 * @param pass
 * @return true - name and password already exists in db.
 * false -  name and password not exists in db.
 */
public boolean dataAlreadyExists(String name, String pass) {
    SQLiteDatabase db =...;
   String query="SELECT COUNT(*) FROM " + TABLE_NAME + " WHERE NAME ="+name+ " PASS ="+pass+";";
long count = DatabaseUtils.queryNumEntries(db,query,null);
    return count > 0;
}

如何检查Android数据库中是否已存在该记录

2 个答案: