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我正在 c# winform 中更新数据库中的数据。当我更新时，如果我的数据中有相同的 IDnum，我不希望它更新。我的 bool 方法有问题。

    public bool ExistsKey(string keyField, string table, string value, SqlConnection con){      
    try {
    if(con.State != ConnectionState.Open) con.Open();
    using(SqlCommand com = new SqlCommand(
            string.Format("IF EXISTS(SELECT * FROM {0} WHERE {1}='{2}') SELECT 1 ELSE SELECT 0", 
                         table, keyField, value), con){
 var result = com.ExecuteScalar();
 return result != null && (int)result == 1;
     }
     } catch {
return false;
     }
     finally {
          con.Close();
     }      
     }

    public void Update()
    {
        if (ExistsKey("idnum", "TableVotersInfo", _idnum.ToString(), sc))
        {
            MessageBox.Show("ID number already exist!");
            FAddVoters._cleardata = "0";
            FAddVoters._checkID = checkID;
        }
        else
        {
            if (sc.State != ConnectionState.Open) sc.Open();
            try
            {
                using (cmd = new SqlCommand(@"UPDATE TableVotersInfo SET Education=@ed, idnum=@idnum, FirstName=@firstname, MiddleName=@middlename, LastName=@lastname, SchoolYear=@schoolyear, ControlNum=@controlnum WHERE id=@id
                                        SELECT @ed, @idnum, @firstname, @middlename, @lastname, @schoolyear, @controlnum
                                        WHERE @id NOT IN (SELECT idNum FROM TableVotersInfo);", sc))
                {
                    cmd.Parameters.AddWithValue("@id", _id);
                    cmd.Parameters.AddWithValue("@ed", _ed);
                    cmd.Parameters.AddWithValue("@idnum", _idnum);
                    cmd.Parameters.AddWithValue("@firstname", _firstname);
                    cmd.Parameters.AddWithValue("@middlename", _middlename);
                    cmd.Parameters.AddWithValue("@lastname", _lastname);
                    cmd.Parameters.AddWithValue("@schoolyear", _schoolyear);
                    cmd.Parameters.AddWithValue("@controlnum", _controlnum);

                    cmd.ExecuteNonQuery();// <-- this is what you want
                    MessageBox.Show("Data Successfully Updated!");
                    FAddVoters._cleardata = cleardata;
                    FAddVoters._checkID = "0";
                }
            } 
            catch (SqlException ex) 
            {
                if(ex.Number == 2627)//duplicated primary key 
                {
                   MessageBox.Show("ID number already exist!");
                   FAddVoters._cleardata = "0";
                   FAddVoters._checkID = checkID;
                } else 
                {
                   MessageBox.Show("There was some error while attempting to update!\nTry again later.");
                }
            }
            finally 
            {
                sc.Close();
            }
        }
    }

我在这里做错了什么？问题出在我的bool.

一些错误，例如

var result = com.ExecuteScalar();= '无效的初始化器成员声明器。'

我的桌子

我的桌子
（来源：akamaihd.net）

4

2 回答 2

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好吧，如果您仔细查看代码：

using(SqlCommand com = new SqlCommand(
        string.Format("IF EXISTS(SELECT * FROM {0} WHERE {1}='{2}') SELECT 1 ELSE SELECT 0", 
                     table, keyField, value), con){

“con)”后缺少一个括号，导致编译器认为其余部分是 SqlCommand 构造初始化程序的一部分。如果您放入缺少的括号，一切都会好起来的:)

using(SqlCommand com = new SqlCommand(
        string.Format("IF EXISTS(SELECT * FROM {0} WHERE {1}='{2}') SELECT 1 ELSE SELECT 0", 
                     table, keyField, value), con)) {
于 2013-10-31T05:56:08.187 回答
0

因为 id 列是int您不需要单个 qoutes。试试下面

"IF EXISTS(SELECT * FROM {0} WHERE {1}={2}) SELECT 1 ELSE SELECT 0"

代码 ：

using(SqlCommand com = new SqlCommand(
            string.Format("IF EXISTS(SELECT * FROM {0} WHERE {1}={2}) SELECT 1 ELSE SELECT 0", 
                         table, keyField, value), con))
{
    var result = com.ExecuteScalar();
    return result != null && (int)result == 1;
}
于 2013-10-31T05:56:36.853 回答