我目前正在为大学的第二个编程课工作，并且在按数据库搜索特定员工姓名时遇到问题，如果用户输入了不在数据库中的用户名，程序崩溃给出错误，而不是显示我创建的错误消息。
搜索方法：
public void searchNameDbMethod()
{
OleDbConnection Myconnection = null;
OleDbDataReader dbReader = null;
string selectionText = "";
bool errorFlag = true;
do
{
string searchName = "";
Console.Write("Search for Employee Name: ");
searchName = Console.ReadLine();
searchName = searchName.ToUpper();
Console.WriteLine("\n");
Myconnection = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0; Data Source= payrolldb.accdb");
Myconnection.Open();
selectionText = "SELECT * FROM Table1;";
OleDbCommand cmd = Myconnection.CreateCommand();
cmd.CommandText = selectionText;
dbReader = cmd.ExecuteReader();
if (dbReader.HasRows)
{
while (dbReader.Read())
{
// since the query produces one column, the GetValue(0)
//must be set
// with multiple column queries, you have to know which
//column holds
// the value that you are looking for
//field 0 = ID
dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
if (dbName == searchName)
{
dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
dbID = dbReader.GetValue(2).ToString(); //2 is field 2 of the db
dbHourlyWage = dbReader.GetValue(3).ToString();
dbDependents = dbReader.GetValue(4).ToString();
Console.Clear();
Console.ResetColor();
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("*******************************************************");
Console.WriteLine("**************** {0} *****************", date);
Console.WriteLine("*******************************************************");
Console.WriteLine("Employee Name: ", dbName);
Console.WriteLine("Employee ID: {0}", dbID);
Console.WriteLine("Hourly Wage: {0}", dbHourlyWage);
Console.WriteLine("Number of Dependents: {0}", dbDependents);
Console.WriteLine("*******************************************************");
Console.ResetColor();
Console.Write("\n\n");
errorFlag = false;
}//closes if
}// end of while
}// end of if
if (errorFlag == true)
{
Console.ResetColor();
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Name is not in our database!");//shows the data accumulated from above
Console.ResetColor();
}//closes if
dbReader.Close();
Myconnection.Close();
}//close do
while (errorFlag == true);
}//closes searchNameDbMethod
请记住，我正在为此项目使用Microsoft Access作为我的数据库（不确定是否重要）。
如何在数据库中找到名称，以便在链接的图像中显示我创建的错误消息而不是错误（崩溃程序）？
答案 0 :(得分：1)
我认为您应该在SQL-Where-Clause中搜索您的员工。
selectionText = "SELECT * FROM Table1 WHERE <EmployeeName> like @Name;";
并在SQL-Query中添加一个参数。
一般我会写这样的代码：
void searchNameDbMethod()
{
OleDbConnection Myconnection = null;
OleDbDataReader dbReader = null;
string selectionText = "";
string searchName = "";
Console.Write("Search for Employee Name: ");
searchName = Console.ReadLine();
searchName = searchName.ToUpper();
Console.WriteLine("\n");
Myconnection = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0; Data Source= payrolldb.accdb");
Myconnection.Open();
selectionText = "SELECT * FROM Table1 WHERE Employee like @Name;";
OleDbCommand cmd = Myconnection.CreateCommand();
cmd.CommandText = selectionText;
cmd.Parameters.Add(new OleDbParameter() { ParameterName = "@Name", Value = searchName, DbType = System.Data.DbType.String });
try
{
dbReader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
while (dbReader.Read())
{
// since the query produces one column, the GetValue(0)
//must be set
// with multiple column queries, you have to know which
//column holds
// the value that you are looking for
//field 0 = ID
string dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
if (dbName == searchName)
{
dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
string dbID = dbReader.GetValue(2).ToString(); //2 is field 2 of the db
string dbHourlyWage = dbReader.GetValue(3).ToString();
string dbDependents = dbReader.GetValue(4).ToString();
Console.Clear();
Console.ResetColor();
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("*******************************************************");
Console.WriteLine("**************** {0} *****************", date);
Console.WriteLine("*******************************************************");
Console.WriteLine("Employee Name: ", dbName);
Console.WriteLine("Employee ID: {0}", dbID);
Console.WriteLine("Hourly Wage: {0}", dbHourlyWage);
Console.WriteLine("Number of Dependents: {0}", dbDependents);
Console.WriteLine("*******************************************************");
Console.ResetColor();
Console.Write("\n\n");
}
}
}
catch
{
if (dbReader != null)
{
dbReader.Close();
}
}
finally
{
if (Myconnection != null)
{
Myconnection.Close();
}
}
}
只是一个例子，以改善您的解决方案。
答案 1 :(得分：0)
我能够根据@BendEg
提供的一些代码来确定它以下是我的所作所为：
public void searchNameDbMethod()
{
OleDbConnection Myconnection = null;
OleDbDataReader dbReader = null;
string selectionText = "";
bool errorFlag = true;
do
{
string searchName = "";
Console.Write("Search for Employee Name: ");
searchName = Console.ReadLine();
searchName = searchName.ToUpper();
Console.WriteLine("\n");
Myconnection = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0; Data Source= payrolldb.accdb");
Myconnection.Open();
selectionText = "SELECT * FROM Table1 WHERE employee_name='" + searchName + "'";
OleDbCommand cmd = Myconnection.CreateCommand();
cmd.CommandText = selectionText;
dbReader = cmd.ExecuteReader();
if (dbReader.HasRows)
{
while (dbReader.Read())
{
// since the query produces one column, the GetValue(0)
//must be set
// with multiple column queries, you have to know which
//column holds
// the value that you are looking for
//field 0 = ID
dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
if (dbName == searchName)
{
dbName = dbReader.GetValue(1).ToString(); //1 is field 1 of the db
dbID = dbReader.GetValue(2).ToString(); //2 is field 2 of the db
dbHourlyWage = dbReader.GetValue(3).ToString();
dbDependents = dbReader.GetValue(4).ToString();
Console.Clear();
Console.ResetColor();
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("*******************************************************");
Console.WriteLine("**************** {0} *****************", date);
Console.WriteLine("*******************************************************");
Console.WriteLine("Employee Name: ", dbName);
Console.WriteLine("Employee ID: {0}", dbID);
Console.WriteLine("Hourly Wage: {0}", dbHourlyWage);
Console.WriteLine("Number of Dependents: {0}", dbDependents);
Console.WriteLine("*******************************************************");
Console.ResetColor();
Console.Write("\n\n");
errorFlag = false;
}//closes if
}// end of while
}// end of if
else if (!dbReader.HasRows)
{
Console.ResetColor();
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Name is not in our database!");//shows the data accumulated from above
Console.ResetColor();
}//closes if
dbReader.Close();
Myconnection.Close();
}//close do
while (errorFlag == true);
}//closes searchNameDbMethod
正如你所看到的，我改变了我的查询，就像他建议的那样（但没有额外复杂的东西），并将if（errorFlag == true）语句更改为else if（！dbReader.HasRows）并且它似乎像魅力！