检查是否存在记录

Question

有谁知道如何在运行时只向数据库插入一次数据？因为现在每当我运行我的系统时，数据总会被插入到数据库中。它有什么办法只是插入数据只有一次，即使我已经运行程序多少次？这里是我的代码

public async void getUserName() 
    { 
     LiveConnectClient client = new LiveConnectClient(session); 
     LiveOperationResult operationResultUserID = await client.GetAsync("me"); 
     dynamic resultUserID = operationResultUserID.Result; 

     userID = resultUserID.id; 
     //getUserInfo(); 

     Service1Client client1 = new Service1Client(); 
     name = await client1.RetrieveNameAsync(userID); 
     dob = await client1.RetrieveDOBAsync(userID); 
     aboutMe = await client1.RetrieveAboutMeAsync(userID); 
     country = await client1.RetrieveCountryAsync(userID); 
     email = await client1.RetrieveEmailAddressAsync(userID); 
     gender = await client1.RetrieveGenderAsync(userID); 
     //status = await client1.RetrieveUserStatusAsync(userID); 
     UserImage = await client1.RetrieveUserImgAsync(userID); 
     vote = await client1.retrieveVotesAsync(userID); 
     count = await client1.retrievecountLearningstoryAsync(userID); 


     txtAboutmeDisplay.Text = aboutMe; 
     txtCountryDisplay.Text = country; 
     txtDOBDisplay.Text = dob; 
     txtEmailDisplay.Text = email; 
     txtGenderDisplay.Text = gender; 
     txtName.Text = name; 
     txtvotes.Text = vote; 
     txtCountDisplay.Text = count.ToString(); 

     int numberofvotes = int.Parse(txtvotes.Text); 
     if (numberofvotes >=1000) 
     { 
      txtstars.Text = "Gold"; 
     } 
     else if (numberofvotes >= 700) 
     { 
      txtstars.Text = "Silver"; 
     } 
     else if (numberofvotes >= 500) 
     { 
      txtstars.Text = "Bronze"; 
     } 



      //txtstars.Visibility == false; 
     InMemoryRandomAccessStream randomAccessStream = new InMemoryRandomAccessStream(); 
     DataWriter writer = new DataWriter(randomAccessStream.GetOutputStreamAt(0)); 
     writer.WriteBytes(UserImage); 
     await writer.StoreAsync(); 
     // Create bitmap image 
     BitmapImage b = new BitmapImage(); 
     b.SetSource(randomAccessStream); 
     // Update Image on XAML Page 

     imgProfilePic.Source = b; 

     int countstory = int.Parse(txtCountDisplay.Text); 
     if (countstory >= 7) 
     { 
      achievement = await client1.updateachievementAsync(userID, "wisemen"); 
     } 

     else if (countstory == 6) 
     { 
      achievement = await client1.updateachievementAsync(userID, "Smartboy"); 
     } 
     else if (countstory == 5) 
     { 
      achievement = await client1.insertAchievementAsync(userID, "novice"); 
     } 

    } 

我的web服务代码

public string insertAchievement(string userid, string achievements) 
    { 
     SqlConnection con = new SqlConnection(connectionString); 

     con.Open(); 
     string insertInterBadges = "Insert into [Achievement] (UserID, Achievement) VALUES " + " (@userid,@achievements)"; 
     SqlCommand cmd = new SqlCommand(insertInterBadges, con); 
     cmd.Parameters.AddWithValue("@userId", userid); 
     cmd.Parameters.AddWithValue("@achievements", achievements); 

     int check = cmd.ExecuteNonQuery(); 
     con.Close(); 
     if (check > 0) 
     { 
      return "Success"; 
     } 
     else 
     { 
      return "Fail"; 
     } 
    } 


    public string updateachievements(string userid, string achievements) 
    { 
     SqlConnection con = new SqlConnection(connectionString); 

     con.Open(); 
     string updateAchievements = "UPDATE Achievement SET Achievement=@achievement Where UserID=@userid"; 
     SqlCommand cmd = new SqlCommand(updateAchievements, con); 
     cmd.Parameters.AddWithValue("@userId", userid); 
     cmd.Parameters.AddWithValue("@achievement", achievements); 

     int check = cmd.ExecuteNonQuery(); 
     con.Close(); 
     if (check > 0) 
     { 
      return "Success"; 
     } 
     else 
     { 
      return "Fail"; 
     } 

    } 

我reference.cs

[System.ServiceModel.OperationContractAttribute(Action = "http://tempuri.org/IService1/updateachievement", ReplyAction = "http://tempuri.org/IService1/updateachievement")] 
    System.Threading.Tasks.Task<string> updateachievementAsync(string userId, string achievements); 

    [System.ServiceModel.OperationContractAttribute(Action = "http://tempuri.org/IService1/insertAchievement", ReplyAction = "http://tempuri.org/IService1/insertAchievement")] 
    System.Threading.Tasks.Task<string> insertAchievementAsync(string userId, string achievements); 

public System.Threading.Tasks.Task<string> updateachievementAsync(string userId, string achievements) 
    { 
     return base.Channel.insertAchievementAsync(userId, achievements); 
    } 

    public System.Threading.Tasks.Task <string> insertAchievementAsync(string userId, string achievements) 
    { 
     return base.Channel.insertAchievementAsync(userId, achievements); 
    } 

我使用web服务的方式

Answer 1

通过你的代码的外观，特别是UPDATE声明中，单个用户只能分配一个成就。该限制使得在UserId, AcheivementId上创建唯一索引变得不那么可行（该索引如果创建，将通过SQL插入错误防止重复条目）。

的替代方案中，更正确的，解决方案是将表中查询插入看之前如果已存在的值：

SELECT COUNT(*) FROM Achievement WHERE UserId = @userId AND Achievement = @achievement 

这可以在一个块中使用，如：

using (SqlConnection conn = new SqlConnection(connectionString)) { 
    conn.Open(); 
    bool isNewValue = true; 
    using (SqlCommand cmd = new SqlCommand("SELECT COUNT(*) FROM Achievement WHERE UserId = @userId AND Achievement = @achievement")) { 
     cmd.Parameters.AddWithValue("@userId", userid); 
     cmd.Parameters.AddWithValue("@achievement", achievements); 
     isNewValue = ((int)cmd.ExecuteScalar() == 0); 
    } 

    if (isNewValue) { 
     // insert user achievement/etc 
    } 
}