SqlHelper并不包含“ConnectionString”的定义
from1错误行为:SqlHelper.ExecuteNonQuery(SqlHelper.ConnectionString, CommandType.Text, sql);
以下为sqlhelper.cs代码内含有ExecuteNonQuery的代码
public static int ExecuteNonQuery(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
{

SqlCommand cmd = new SqlCommand();

using (SqlConnection conn = new SqlConnection(connectionString))
{
PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);
int val = cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
return val;
}
}

public static int ExecuteNonQuery(SqlConnection connection, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
{

SqlCommand cmd = new SqlCommand();

PrepareCommand(cmd, connection, null, cmdType, cmdText, commandParameters);
int val = cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
return val;
}

public static int ExecuteNonQuery(SqlTransaction trans, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
{
SqlCommand cmd = new SqlCommand();
PrepareCommand(cmd, trans.Connection, trans, cmdType, cmdText, commandParameters);
int val = cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
return val;
}

[解决办法]
查下代码，看看你的SQLHelper类的ConnectionString属性，没有 自己填一个
[解决办法]

C# code

public string ConnectionString{get;set;}
[解决办法]
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怎么添加啊?能给一个简单的添加过程吗?偶是菜鸟

[解决办法]
楼上的非常正确