Question

FileInputStream fis = new FileInputStream("hashmap.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
extras = (HashMap) ois.readObject();
ois.close();
fis.close();

我的visitorcompany班：

public void addintovisitor()
{
string companyname = (txtvisitor.Text.ToUpper());
DataSet result = new DataSet();
visitorcompany vc = new visitorcompany();
string Location1 = Convert.ToString(Session["location"]);
vc.checksamecompanyname(ref result, Location1);
for (int i = 0; i < result.Tables["details"].Rows.Count; i++)
{
if (companyname == result.Tables["details"].Rows[i]["Companyname"].ToString())
{

}
else
{
 string strConn = Convert.ToString(ConfigurationManager.ConnectionStrings["connectionstring"]);
 SqlConnection conn = new SqlConnection(strConn);
 SqlCommand cmd = new SqlCommand(
                  "INSERT INTO tblVisitorcompany ([CompanyName], " +
                  "[Location1]) " +
                  "VALUES(@CompanyName, @Location1)", conn);

                cmd.Parameters.AddWithValue("@Companyname", companyname);
                cmd.Parameters.AddWithValue("@Location1", Location1);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
 }
 }
 }

我正在尝试一次搜索一行，以检查sql表是否具有相同的公司名称。如果已经存在公司名称，则该程序将不执行任何操作。如果这是新的公司名称，则程序会将公司名称添加到sql表中。但是，添加新公司名称时，该程序将添加多次。有人可以帮我重新编辑程序，使其仅添加一个新的公司名称。非常感谢。

Answer 1

不要使用companyname作为插入命令的参数，因为它在for循环中保持不变。请改用result.Tables["details"].Rows[i]["Companyname"].ToString()：

...
cmd.Parameters.AddWithValue("@Companyname", result.Tables["details"].Rows[i]["Companyname"].ToString());
...

Answer 2

检查值是否存在，如果没有，请然后添加。
代码中的一个简单更改：

bool valueFound = false;

// check if the value exists
for (int i = 0; i < result.Tables["details"].Rows.Count; i++)
{
    if (companyname == result.Tables["details"].Rows[i]["Companyname"].ToString())
    {
        // it exists so we exit the loop
        valueFound = true;
        break;
    }
}

// we have looped all the way without finding the value, so we can insert
if(!valueFound)
{
    string strConn = Convert.ToString(ConfigurationManager.ConnectionStrings["connectionstring"]);
    SqlConnection conn = new SqlConnection(strConn);
    SqlCommand cmd = new SqlCommand(
          "INSERT INTO tblVisitorcompany ([CompanyName], " +
          "[Location1]) " +
          "VALUES(@CompanyName, @Location1)", conn);

     cmd.Parameters.AddWithValue("@Companyname", companyname);
     cmd.Parameters.AddWithValue("@Location1", Location1);
     conn.Open();
     cmd.ExecuteNonQuery();
     conn.Close();
}

当然，您可以检查值是否以更有效的方式存在，但这至少应该可以解决您的特定问题。

Answer 3

using( var connection = new SqlConnection( "my connection string" ) ) {
using( var command = connection.CreateCommand() ) {
    command.CommandText = "SELECT Column1, Column2, Column3 FROM myTable";

    connection.Open();
    using( var reader = command.ExecuteReader() ) {
        var indexOfColumn1 = reader.GetOrdinal( "Column1" );
        var indexOfColumn2 = reader.GetOrdinal( "Column2" );
        var indexOfColumn3 = reader.GetOrdinal( "Column3" );

        while( reader.Read() ) {
            var value1 = reader.GetValue( indexOfColumn1 );
            var value2 = reader.GetValue( indexOfColumn2 );
            var value3 = reader.GetValue( indexOfColumn3 );

            // now, do something what you want
        }
    }
    connection.Close();
}

一次读取SQL C＃

3 个答案: