Question

我想检查数据库中是否存在几个值。如果是，则如果游标为null，则该方法应返回TRUE或FALSE。但问题是尽管值不在数据库中，它仍会一直返回TRUE！我错过了什么？

    // This method check if the combination image path and contact name already exists in database
public boolean checkContentDatabase(String imageFilePath, String contactName) {

    String query = "Select * from " + DB_TABLE+ " where " + TABLE_IMAGE_PATH + "='" + imageFilePath + "' and " + TABLE_CONTACT_NAME + "='" + contactName +"' ;";

    Cursor c = db.rawQuery(query, null);

    if(c != null) // Exists in database
     {
     return true;
     }
     else
     {
         return false;
     }
}

Answer 1

将if条件替换为：

if(c.getCount() > 0)
 {
 return true;
 }
 else
 {
     return false;
 }

Answer 2

使用c != null && c.getCount() > 0代替c != null

Answer 3

      public boolean checkContentDatabase(String imageFilePath, String contactName) {

String query = "Select * from " + DB_TABLE+ " where " + TABLE_IMAGE_PATH      + "='"          +          imageFilePath + "' and " + TABLE_CONTACT_NAME + "='" + contactName +"' ;";

Cursor c = db.rawQuery(query, null);


           c.moveToFirst();
    if(c.isAfterLast() == false) {
       return true;
      }
     else
       {
      return false;
      }
     }

Answer 4

游标不为null，因为它已成功创建。只有您的结果集不存在。尝试使用“SELECT 1 FROM ...”，然后检查结果是否等于1.

检查数据库中是否存在值

4 个答案: