如何检查SQLite中为Android的表行是否存在 [英] how to check whether row exists or not in a table of sqlite for android

问题描述

我要检查的SQLite表的行是否在数据库中存在或not..If行存在我应该叫一类，否则另一个class.To得到这个功能，我使用

I want to check whether a row of the sqlite table exists in database or not..If row exists i should call a class otherwise another class.To get this functionality i am using

  public boolean Exists(int position) {

       SQLiteDatabase db =  (placeData).getReadableDatabase();
        Cursor cursor = db.rawQuery("select * from pages where bbookid ='"+ position +"'", null);

       boolean exists = (cursor.getColumnName(position)) != null;
       Log.i("logs","fads");
       if(exists=true)
       {
           getDataAndPopulate();
       }
       else
       {
       Log.i("qefw","cursors");
       new LoadAllProducts().execute();
       }
       cursor.close();
       return exists;
    }

但使用这种code中的行重新插入..Could有人建议我接近的功能的方法。

but using this code the rows are reinserting ..Could anyone suggest me the way to approach the functionality

推荐答案

您平等检查失败，因为这个前pression被评估为真正：

Your equality check is failing because this expression is evaluating to true:

if(exists=true)

当你有一个等号，这意味着的分配的。您正在分配真正到存在，而不是比较存在到真正。分配的结果是值到存在被分配（真正）。

When you have a single equals sign, it means assignment. You are assigning true to exists, instead of comparing exists to true. The result of the assignment is the value to which exists was assigned (true).

尝试适当平等的操盘手：

Try the proper equality operator instead:

if (exists == true)

请参阅此相关的帖子再看看这个问题。

See this related post for another look at this issue.

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