Question

我有一个专门的KQ数据库,我想做的是用户选择一个过滤器。例如,有一个图书数据库,用户只是想从“Agata christies书”中查找数据。

因此,我选择了一种选择,然后打算将所选择的田地转至另一个执行询问的活动。

我的问题是,如何使问题充满活力? 想一去1个以上的过滤器,如何根据从其他活动获得的数据,使“WHERE”条款成为一种意图?

感谢

Answer 1

Lazy way but tried and true:

String query = "Select id FROM books WHERE 1=1"
if (condition1) query+= " AND name="+theName;
if (condition2) query+= " AND author="+theAuthor;
if (condition3) query+= " AND price="+thePrice;

If you have full control of options aka via spinners, this is safe. If its an edittext, use preparedStatements and bind the arguments to avoid SQLI.

Answer 2

public Cursor Query(String sql, String[] selectedArgs)

Generate Stringkou with ? for binding and add debate in selected Args.

Answer 3

但这并不是这样做的最佳方式,但假定你事先知道,你可以有1个ger化过滤器(price)和1个str过滤器(作者名称),我试图:

SELECT * FROM BOOKS WHERE (price<0 OR AND BOOKS.price = price ) AND (author="" OR BOOKS.author = author);

I m 不是专家,请检查Syntax。陷阱在这里是为了确定价格和带;如果过滤器没有固定,则0(所有线都考虑在内,因为情况是价格的调整;0是真实的),并且将作者作为空洞,不过滤提交人(SlectT不会过滤这些线,因为情况是真实的)。

这将发挥作用!

Answer 4

boolean filterName = false;
boolean filterPrice = false;
ArrayList<String> selectionArgs = new ArrayList<String>();
String query = "SELECT * FROM BOOKS WHERE 1=1";
if(filterName) {
    selectionArgs.add(searchString);
    query += " AND NAME = ?";
}
if(filterPrice) {
    selectionArgs.add(priceString);
    query += " AND PRICE= ?";
}

Cursor c = m_Database.rawQuery(query, (String[])selectionArgs1.toArray());

Answer 5

引证这一点,用学生数据作为实例的Im

public ArrayList<Student>getStudent(int stdID,String stdName)
{
ArrayList<Student> studentArr = new ArrayList<>();
 SQLiteDatabase db = this.getReadableDatabase();
 Cursor cursor = null;

String sqlQuery = "SELECT * FROM tblstudent WHERE 1=1";
String sqlParam = "";

/*Here we re building the dynamic sql.*/

if(stdID > 0)
{
sqlQuery += " AND std_id = ?";
sqlParam = String.valueOf(stdID);
}

if(!stdName.trim().isEmpty())
{
sqlQuery += " AND std_name = ?";
sqlParam = stdName.trim();
}

/*Do this to avoid SQL injection Attack (SIA) [it s very important!]*/
sqlParam = sqlParam.replaceAll(";|--","");


 if (db != null) {
    
  if (!sqlParam.isEmpty()) {

    cursor = db.rawQuery(SQL,new String[]{sqlParam});
        
    }else {
   /*if  the "sqlParam" is empty.*/

   cursor = db.rawQuery(SQL,null);
    }
 if (cursor != null && cursor.getCount()>0) {

 while(cursor.moveToNext()){

Student stdmodel = new Student();

stdmodel.setstdID(cursor.getInt(0));
stdmodel.stdName(cursor.getString(1));

studentArr.add(stdmodel);
}

 cursor.close();
  }
}

return studentArr;
}

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