Question

我编写了一种搜索数据库的方法，根据模块查找匹配的讲师。但是，当我运行它时，它会为所有三个保存相同的名称！

以下是方法：

public List<tableModules> getStudentsLecturers(String mod1, String mod2, String mod3) {
        List<tableModules> studentModuleLecturer = new ArrayList<tableModules>();       
        // Select All Query to find lecturers depending on modules      
        Log.d("Lecturers", mod1);
        Log.d("Lecturers", mod2);
        Log.d("Lecturers", mod3);
        String selectQuery = "SELECT DISTINCT " + Module_Lecturer + " FROM " + Table2 + " WHERE " + Module_Name + " = \'" + mod1 + "\' OR \'" + mod2 + "\' OR \'" + mod3 + "\'";
        Log.d("1", "1");
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {               
                tableModules  moduleLecturers = new tableModules();             
                moduleLecturers.modulelecturer = cursor.getString(0);          
                studentModuleLecturer.add(moduleLecturers);         
            } while (cursor.moveToNext());
        }
        // return lecture list
        return studentModuleLecturer;       
    }

然后在 MainActivity.java

中调用

List<tableModules> lecturers = db.getStudentsLecturers(mod1, mod2, mod3);
                if (!lecturers.isEmpty())
                {           
                for (tableModules session: lecturers)
                {
                    Editor editor = preferences.edit();
                    //Save lecturers to list
                    for (int i=0; i < lecturers.size(); i++) {
                        if (counter == 0)
                        {                    
                        lecturer1 = session.modulelecturer.toString();
                        editor.putString("lec1", lecturer1);
                        Log.d("Lecs", "1"); 
                        editor.commit();
                        counter++;
                        }
                        if (counter == 1)
                        {                   
                        lecturer2 = session.modulelecturer.toString();
                        editor.putString("lec2", lecturer2);
                        Log.d("Lecs", "2"); 
                        editor.commit();
                        counter++;
                        }
                        if (counter == 2)
                        {   
                        lecturer3 = session.modulelecturer.toString();
                        editor.putString("lec3", lecturer3);
                        Log.d("Lecs", "3"); 
                        editor.commit();
                        counter++;
                        }
                        else
                        {                               
                            Log.d("Lecs", "ERROR"); 
                        }
                     }

我得到了我保存相同的＆＃34; session.modulelecturer.toString（）;＆＃34;对于每一个，但我无法弄清楚如何改变SQL方法来为所有三个单独的模块选择所有三个讲师。

Answer 1

尝试替换

" WHERE " + Module_Name + " = \'" + mod1 + "\' OR \'" + mod2 + "\' OR \'" + mod3 + "\'";

与

" WHERE " + Module_Name + " = '" + mod1 + "' OR " + Module_Name + " = '" + mod2 + "' OR " + Module_Name + " = '" + mod3 + "'";

在实践中，你不能说

WHERE ModuleName = 'This' OR 'That'

但你可以说

WHERE ModuleName = 'This' OR ModuleName = 'That'

我知道为每个可能的值重写列名是一种拖累，但它是如何在SQL中工作的。

或者，您可以编写更紧凑的表单：

WHERE ModuleName IN ('This', 'That', '...')

所以你的查询可以变成：

" WHERE " + Module_Name + " IN ('" + mod1 + "', '" + mod2 + "', '" + mod3 + "')";

重写SQLite语句SELECT WHERE - Android Eclipse

1 个答案: