C# SqlParameterCollection仅接受非null的SqlParameter类型对象，而不接受DBNull对象

每当我在文本框中键入nothing或null值时，就会出现一个错误。我的代码如下：

 SqlCommand cmd = con.CreateCommand();
 cmd.CommandText = "INSERT INTO Records 
                   ([Student ID], [First Name], [Last Name], [Middle Initial], 
                     Gender, Address, Status, Year, Email, Course, 
                    [Contact Number]) 
                    VALUES (@StudentID, @FirstName, @LastName , @MiddleInitial, 
                            @Gender, @Address, @Status, @Year, @Email, @Course, 
                            @ContactNumber)";

   SqlParameter p1 = new SqlParameter("@StudentID", SqlDbType.NChar);
   p1.Value = textBox1.Text;
   cmd.Parameters.Add(p1);
   SqlParameter p2 = new SqlParameter("@FirstName", SqlDbType.NVarChar);
   p2.Value = textBox2.Text;
   cmd.Parameters.Add(p2);
   SqlParameter p3 = new SqlParameter("@LastName", SqlDbType.NVarChar);
   p3.Value = textBox3.Text;
   cmd.Parameters.Add(p3);
   SqlParameter p4 = new SqlParameter("@MiddleInitial", SqlDbType.NChar);
   p4.Value = comboBox1.Text;
   cmd.Parameters.Add(p4);
   SqlParameter p5 = new SqlParameter("@Gender", SqlDbType.NChar);
   p5.Value = comboBox2.Text;
   cmd.Parameters.Add(p5);
   SqlParameter p6 = new SqlParameter("@Address", SqlDbType.VarChar);
   p6.Value = textBox4.Text;
   cmd.Parameters.Add(p6);
   SqlParameter p7 = new SqlParameter("@Status", SqlDbType.NChar);
   p7.Value = comboBox3.Text;
   cmd.Parameters.Add(p7);
   SqlParameter p8 = new SqlParameter("@Year", SqlDbType.VarChar);
   p8.Value = comboBox4.Text;
   cmd.Parameters.Add(p8);
   SqlParameter p9 = new SqlParameter("@Email", SqlDbType.VarChar);
   p9.Value = textBox5.Text;
   cmd.Parameters.Add(p9);
   SqlParameter p10 = new SqlParameter("@Course", SqlDbType.VarChar);
   p10.Value = comboBox5.Text;
   cmd.Parameters.Add(p10);
   SqlParameter p11 = new SqlParameter("@ContactNumber", SqlDbType.VarChar);
   p11.Value = textBox6.Text;
   cmd.Parameters.Add(p11);

   textBox1.Text = "";
   textBox2.Text = "";
   textBox3.Text = "";
   textBox4.Text = "";
   textBox5.Text = "";
   textBox6.Text = "";
   comboBox1.Text = "";
   comboBox2.Text = "";
   comboBox3.Text = "";
   comboBox4.Text = "";
   comboBox5.Text = "";
   if (cmd.Parameters.Contains(System.DBNull.Value))
   {
       MessageBox.Show("Please complete the fields", "Information...", 
                       MessageBoxButtons.OK, MessageBoxIcon.Warning, 
                       MessageBoxDefaultButton.Button1);
    }
    else
    {
       MessageBox.Show("Data Inserted!", "Information ... ", 
                       MessageBoxButtons.OK, MessageBoxIcon.Information, 
                       MessageBoxDefaultButton.Button1);
    }
    cmd.ExecuteNonQuery();
    con.Close();

if ( cmd.Parameters.Any(p => DBNull.Value.Equals(p.Value)) )

if ( cmd.Parameters.Any(p => string.IsNullOrWhiteSpace((string)p.Value)) )

public class Student
{
    public int StudentId {get;set;}
    public string FirstName {get;set;}
    public string FirstName {get;set;}
    public string MiddleInitial{get;set;} // upto ContactNumber or as required.
 }

错误发生在：

if(cmd.Parameters.Contains(System.DBNull.Value))

---

我使用的是SQL Server和C#。

首先，您需要查找任何参数的value属性是否为DBNull。您正在尝试检查参数对象本身是否为DBNull，但您应该查看Value属性。您可以这样做：

 SqlCommand cmd = con.CreateCommand();
 cmd.CommandText = "INSERT INTO Records 
                   ([Student ID], [First Name], [Last Name], [Middle Initial], 
                     Gender, Address, Status, Year, Email, Course, 
                    [Contact Number]) 
                    VALUES (@StudentID, @FirstName, @LastName , @MiddleInitial, 
                            @Gender, @Address, @Status, @Year, @Email, @Course, 
                            @ContactNumber)";

   SqlParameter p1 = new SqlParameter("@StudentID", SqlDbType.NChar);
   p1.Value = textBox1.Text;
   cmd.Parameters.Add(p1);
   SqlParameter p2 = new SqlParameter("@FirstName", SqlDbType.NVarChar);
   p2.Value = textBox2.Text;
   cmd.Parameters.Add(p2);
   SqlParameter p3 = new SqlParameter("@LastName", SqlDbType.NVarChar);
   p3.Value = textBox3.Text;
   cmd.Parameters.Add(p3);
   SqlParameter p4 = new SqlParameter("@MiddleInitial", SqlDbType.NChar);
   p4.Value = comboBox1.Text;
   cmd.Parameters.Add(p4);
   SqlParameter p5 = new SqlParameter("@Gender", SqlDbType.NChar);
   p5.Value = comboBox2.Text;
   cmd.Parameters.Add(p5);
   SqlParameter p6 = new SqlParameter("@Address", SqlDbType.VarChar);
   p6.Value = textBox4.Text;
   cmd.Parameters.Add(p6);
   SqlParameter p7 = new SqlParameter("@Status", SqlDbType.NChar);
   p7.Value = comboBox3.Text;
   cmd.Parameters.Add(p7);
   SqlParameter p8 = new SqlParameter("@Year", SqlDbType.VarChar);
   p8.Value = comboBox4.Text;
   cmd.Parameters.Add(p8);
   SqlParameter p9 = new SqlParameter("@Email", SqlDbType.VarChar);
   p9.Value = textBox5.Text;
   cmd.Parameters.Add(p9);
   SqlParameter p10 = new SqlParameter("@Course", SqlDbType.VarChar);
   p10.Value = comboBox5.Text;
   cmd.Parameters.Add(p10);
   SqlParameter p11 = new SqlParameter("@ContactNumber", SqlDbType.VarChar);
   p11.Value = textBox6.Text;
   cmd.Parameters.Add(p11);

   textBox1.Text = "";
   textBox2.Text = "";
   textBox3.Text = "";
   textBox4.Text = "";
   textBox5.Text = "";
   textBox6.Text = "";
   comboBox1.Text = "";
   comboBox2.Text = "";
   comboBox3.Text = "";
   comboBox4.Text = "";
   comboBox5.Text = "";
   if (cmd.Parameters.Contains(System.DBNull.Value))
   {
       MessageBox.Show("Please complete the fields", "Information...", 
                       MessageBoxButtons.OK, MessageBoxIcon.Warning, 
                       MessageBoxDefaultButton.Button1);
    }
    else
    {
       MessageBox.Show("Data Inserted!", "Information ... ", 
                       MessageBoxButtons.OK, MessageBoxIcon.Information, 
                       MessageBoxDefaultButton.Button1);
    }
    cmd.ExecuteNonQuery();
    con.Close();

if ( cmd.Parameters.Any(p => DBNull.Value.Equals(p.Value)) )

if ( cmd.Parameters.Any(p => string.IsNullOrWhiteSpace((string)p.Value)) )

public class Student
{
    public int StudentId {get;set;}
    public string FirstName {get;set;}
    public string FirstName {get;set;}
    public string MiddleInitial{get;set;} // upto ContactNumber or as required.
 }

其次，textbox控件的

.Text

属性永远不会为空。最坏情况下，它将是空字符串。所以您真正想要的是这样的代码：

 SqlCommand cmd = con.CreateCommand();
 cmd.CommandText = "INSERT INTO Records 
                   ([Student ID], [First Name], [Last Name], [Middle Initial], 
                     Gender, Address, Status, Year, Email, Course, 
                    [Contact Number]) 
                    VALUES (@StudentID, @FirstName, @LastName , @MiddleInitial, 
                            @Gender, @Address, @Status, @Year, @Email, @Course, 
                            @ContactNumber)";

   SqlParameter p1 = new SqlParameter("@StudentID", SqlDbType.NChar);
   p1.Value = textBox1.Text;
   cmd.Parameters.Add(p1);
   SqlParameter p2 = new SqlParameter("@FirstName", SqlDbType.NVarChar);
   p2.Value = textBox2.Text;
   cmd.Parameters.Add(p2);
   SqlParameter p3 = new SqlParameter("@LastName", SqlDbType.NVarChar);
   p3.Value = textBox3.Text;
   cmd.Parameters.Add(p3);
   SqlParameter p4 = new SqlParameter("@MiddleInitial", SqlDbType.NChar);
   p4.Value = comboBox1.Text;
   cmd.Parameters.Add(p4);
   SqlParameter p5 = new SqlParameter("@Gender", SqlDbType.NChar);
   p5.Value = comboBox2.Text;
   cmd.Parameters.Add(p5);
   SqlParameter p6 = new SqlParameter("@Address", SqlDbType.VarChar);
   p6.Value = textBox4.Text;
   cmd.Parameters.Add(p6);
   SqlParameter p7 = new SqlParameter("@Status", SqlDbType.NChar);
   p7.Value = comboBox3.Text;
   cmd.Parameters.Add(p7);
   SqlParameter p8 = new SqlParameter("@Year", SqlDbType.VarChar);
   p8.Value = comboBox4.Text;
   cmd.Parameters.Add(p8);
   SqlParameter p9 = new SqlParameter("@Email", SqlDbType.VarChar);
   p9.Value = textBox5.Text;
   cmd.Parameters.Add(p9);
   SqlParameter p10 = new SqlParameter("@Course", SqlDbType.VarChar);
   p10.Value = comboBox5.Text;
   cmd.Parameters.Add(p10);
   SqlParameter p11 = new SqlParameter("@ContactNumber", SqlDbType.VarChar);
   p11.Value = textBox6.Text;
   cmd.Parameters.Add(p11);

   textBox1.Text = "";
   textBox2.Text = "";
   textBox3.Text = "";
   textBox4.Text = "";
   textBox5.Text = "";
   textBox6.Text = "";
   comboBox1.Text = "";
   comboBox2.Text = "";
   comboBox3.Text = "";
   comboBox4.Text = "";
   comboBox5.Text = "";
   if (cmd.Parameters.Contains(System.DBNull.Value))
   {
       MessageBox.Show("Please complete the fields", "Information...", 
                       MessageBoxButtons.OK, MessageBoxIcon.Warning, 
                       MessageBoxDefaultButton.Button1);
    }
    else
    {
       MessageBox.Show("Data Inserted!", "Information ... ", 
                       MessageBoxButtons.OK, MessageBoxIcon.Information, 
                       MessageBoxDefaultButton.Button1);
    }
    cmd.ExecuteNonQuery();
    con.Close();

if ( cmd.Parameters.Any(p => DBNull.Value.Equals(p.Value)) )

if ( cmd.Parameters.Any(p => string.IsNullOrWhiteSpace((string)p.Value)) )

public class Student
{
    public int StudentId {get;set;}
    public string FirstName {get;set;}
    public string FirstName {get;set;}
    public string MiddleInitial{get;set;} // upto ContactNumber or as required.
 }

---

最后，顺便说一句，即使

.Text

属性可以是

null

，这与

DBNull

不同。它们是两种不同的东西。

干净有效的方法。将在以后的开发中帮助您。更改代码，如下所示：

 SqlCommand cmd = con.CreateCommand();
 cmd.CommandText = "INSERT INTO Records 
                   ([Student ID], [First Name], [Last Name], [Middle Initial], 
                     Gender, Address, Status, Year, Email, Course, 
                    [Contact Number]) 
                    VALUES (@StudentID, @FirstName, @LastName , @MiddleInitial, 
                            @Gender, @Address, @Status, @Year, @Email, @Course, 
                            @ContactNumber)";

   SqlParameter p1 = new SqlParameter("@StudentID", SqlDbType.NChar);
   p1.Value = textBox1.Text;
   cmd.Parameters.Add(p1);
   SqlParameter p2 = new SqlParameter("@FirstName", SqlDbType.NVarChar);
   p2.Value = textBox2.Text;
   cmd.Parameters.Add(p2);
   SqlParameter p3 = new SqlParameter("@LastName", SqlDbType.NVarChar);
   p3.Value = textBox3.Text;
   cmd.Parameters.Add(p3);
   SqlParameter p4 = new SqlParameter("@MiddleInitial", SqlDbType.NChar);
   p4.Value = comboBox1.Text;
   cmd.Parameters.Add(p4);
   SqlParameter p5 = new SqlParameter("@Gender", SqlDbType.NChar);
   p5.Value = comboBox2.Text;
   cmd.Parameters.Add(p5);
   SqlParameter p6 = new SqlParameter("@Address", SqlDbType.VarChar);
   p6.Value = textBox4.Text;
   cmd.Parameters.Add(p6);
   SqlParameter p7 = new SqlParameter("@Status", SqlDbType.NChar);
   p7.Value = comboBox3.Text;
   cmd.Parameters.Add(p7);
   SqlParameter p8 = new SqlParameter("@Year", SqlDbType.VarChar);
   p8.Value = comboBox4.Text;
   cmd.Parameters.Add(p8);
   SqlParameter p9 = new SqlParameter("@Email", SqlDbType.VarChar);
   p9.Value = textBox5.Text;
   cmd.Parameters.Add(p9);
   SqlParameter p10 = new SqlParameter("@Course", SqlDbType.VarChar);
   p10.Value = comboBox5.Text;
   cmd.Parameters.Add(p10);
   SqlParameter p11 = new SqlParameter("@ContactNumber", SqlDbType.VarChar);
   p11.Value = textBox6.Text;
   cmd.Parameters.Add(p11);

   textBox1.Text = "";
   textBox2.Text = "";
   textBox3.Text = "";
   textBox4.Text = "";
   textBox5.Text = "";
   textBox6.Text = "";
   comboBox1.Text = "";
   comboBox2.Text = "";
   comboBox3.Text = "";
   comboBox4.Text = "";
   comboBox5.Text = "";
   if (cmd.Parameters.Contains(System.DBNull.Value))
   {
       MessageBox.Show("Please complete the fields", "Information...", 
                       MessageBoxButtons.OK, MessageBoxIcon.Warning, 
                       MessageBoxDefaultButton.Button1);
    }
    else
    {
       MessageBox.Show("Data Inserted!", "Information ... ", 
                       MessageBoxButtons.OK, MessageBoxIcon.Information, 
                       MessageBoxDefaultButton.Button1);
    }
    cmd.ExecuteNonQuery();
    con.Close();

if ( cmd.Parameters.Any(p => DBNull.Value.Equals(p.Value)) )

if ( cmd.Parameters.Any(p => string.IsNullOrWhiteSpace((string)p.Value)) )

public class Student
{
    public int StudentId {get;set;}
    public string FirstName {get;set;}
    public string FirstName {get;set;}
    public string MiddleInitial{get;set;} // upto ContactNumber or as required.
 }

创建一个名为student的类，并在该类中根据需要为

FirstName

、

LastName

和其他对象创建属性。大概是这样的：

 SqlCommand cmd = con.CreateCommand();
 cmd.CommandText = "INSERT INTO Records 
                   ([Student ID], [First Name], [Last Name], [Middle Initial], 
                     Gender, Address, Status, Year, Email, Course, 
                    [Contact Number]) 
                    VALUES (@StudentID, @FirstName, @LastName , @MiddleInitial, 
                            @Gender, @Address, @Status, @Year, @Email, @Course, 
                            @ContactNumber)";

   SqlParameter p1 = new SqlParameter("@StudentID", SqlDbType.NChar);
   p1.Value = textBox1.Text;
   cmd.Parameters.Add(p1);
   SqlParameter p2 = new SqlParameter("@FirstName", SqlDbType.NVarChar);
   p2.Value = textBox2.Text;
   cmd.Parameters.Add(p2);
   SqlParameter p3 = new SqlParameter("@LastName", SqlDbType.NVarChar);
   p3.Value = textBox3.Text;
   cmd.Parameters.Add(p3);
   SqlParameter p4 = new SqlParameter("@MiddleInitial", SqlDbType.NChar);
   p4.Value = comboBox1.Text;
   cmd.Parameters.Add(p4);
   SqlParameter p5 = new SqlParameter("@Gender", SqlDbType.NChar);
   p5.Value = comboBox2.Text;
   cmd.Parameters.Add(p5);
   SqlParameter p6 = new SqlParameter("@Address", SqlDbType.VarChar);
   p6.Value = textBox4.Text;
   cmd.Parameters.Add(p6);
   SqlParameter p7 = new SqlParameter("@Status", SqlDbType.NChar);
   p7.Value = comboBox3.Text;
   cmd.Parameters.Add(p7);
   SqlParameter p8 = new SqlParameter("@Year", SqlDbType.VarChar);
   p8.Value = comboBox4.Text;
   cmd.Parameters.Add(p8);
   SqlParameter p9 = new SqlParameter("@Email", SqlDbType.VarChar);
   p9.Value = textBox5.Text;
   cmd.Parameters.Add(p9);
   SqlParameter p10 = new SqlParameter("@Course", SqlDbType.VarChar);
   p10.Value = comboBox5.Text;
   cmd.Parameters.Add(p10);
   SqlParameter p11 = new SqlParameter("@ContactNumber", SqlDbType.VarChar);
   p11.Value = textBox6.Text;
   cmd.Parameters.Add(p11);

   textBox1.Text = "";
   textBox2.Text = "";
   textBox3.Text = "";
   textBox4.Text = "";
   textBox5.Text = "";
   textBox6.Text = "";
   comboBox1.Text = "";
   comboBox2.Text = "";
   comboBox3.Text = "";
   comboBox4.Text = "";
   comboBox5.Text = "";
   if (cmd.Parameters.Contains(System.DBNull.Value))
   {
       MessageBox.Show("Please complete the fields", "Information...", 
                       MessageBoxButtons.OK, MessageBoxIcon.Warning, 
                       MessageBoxDefaultButton.Button1);
    }
    else
    {
       MessageBox.Show("Data Inserted!", "Information ... ", 
                       MessageBoxButtons.OK, MessageBoxIcon.Information, 
                       MessageBoxDefaultButton.Button1);
    }
    cmd.ExecuteNonQuery();
    con.Close();

if ( cmd.Parameters.Any(p => DBNull.Value.Equals(p.Value)) )

if ( cmd.Parameters.Any(p => string.IsNullOrWhiteSpace((string)p.Value)) )

public class Student
{
    public int StudentId {get;set;}
    public string FirstName {get;set;}
    public string FirstName {get;set;}
    public string MiddleInitial{get;set;} // upto ContactNumber or as required.
 }

创建一个单独的方法，用于将参数分配给

SqlCommand

。在这些方法中，如果需要，您还可以使用三元运算（即？，）进行验证：

private void CreateParameterList(ref Student s, ref SqlCommand cmd)
       {
          var parameters = new []
                               {
                                 new SqlParameter("@FirstName",s.FirstName),
                                 new SqlParameter("@LastName",s.LastName),
                                 :
                                 :
                                  new SqlParameter("@ContactNumber",s.ContactNumber)
                                }
          cmd.Parameters.AddRange(parameters);
       }

创建一个保存方法，并将上述类作为参数传递。您还可以以

Student

的名称创建一个单独的分部类，以便使用同一实例访问成员。调用步骤2中的方法，以便使用参数

protected void MySaveFunction(Student s)
{
    using(SqlConnection con= new SqlConnection(your_Connection_String))
    {
        using(SqlCommmand cmd = new SqlCommand())
        {
            cmd.CommandType = CommandType.Text/StoredProcedure;
            // it depends on what you are using
            cmd.Connection = con;
            cmd.CommandText=Your Query or Name of SP;
            con.Open();
            CreateParameterList(ref s, ref cmd);
            try
            {
                int i = cmd.ExecuteNonQuery();
                if(i>0)
                {
                    //Show Success or return Success
                }        
            }
            catch(SqlException sqlex)
            {
                //catch and log exception
            }
            finally
            {  con.Close(); con.Dispose() }
        }
    }
}

---

为什么不重新开始，在达到这一点之前做一些适当的验证呢？如果没有必要，你永远不应该开始创建对象和东西。所以，帮自己一个忙，添加一个验证方法，如

private bool IsValid()
{
    return !Controls.OfType<TextBox>().Any(c=> String.IsNullOrEmpty(c.Text));
}

---

请记住，这是未经测试的，我现在没有VS，并且所有内容都是手动编写的，因此可能无法以这种方式访问控件集合。

在将任何内容分配给命令参数之前，需要检查所设置的值是否为

null

。如果它是一个文本框，那么您可能需要检查（！string.IsNullOrEmpty（textbox.text））是否

//然后添加参数

我按照您所说的做了，但即使数据为空，它仍会继续插入数据。为什么在

CreateParameterList

中将

Student

和

SqlCommand

声明为ref参数？Student和SqlCommand都是类，因此默认情况下通过引用传递。没有必要使用ref。请看@tuzo我写ref不是强制性的，他必须使用ref。如果你能看到我的代码，我跳过了这么多属性和参数，所以这并不意味着OP也应该跳过这些。上面的代码只是为探索Stuff实现的新方法而给出的建议或提示。如果他能做研究，那么他必须能够找到几十种同样的方法。这取决于他，他需要什么样的方式，他更喜欢什么样的方式？Joel，这段代码不错，但我认为这对中级开发人员和以上级别的开发人员来说肯定是好的，从OP的代码来看，他似乎是新手，不适合从LINQ和匿名之类的东西开始。但是如果他理解了，那么这对他来说真的会很有帮助。