c# - 即使表中的列不允许为空，空文本框仍将数据保存在 SQL Server 中

Question

我遇到了这个问题，当我在所有文本框都为空时单击保存按钮时，它会在所有文本框上显示星号标签。当我填写最后一个文本框而将所有其他文本框留空时，它会将数据保存到带有空字符串的数据库中。

我该如何处理这个问题？

if (tbIDCardNum.Text.Trim() == "")
{
    lblStarIDCardNum.Visibility = Visibility.Visible;
}

if (tbFirstName.Text.Trim() == "")
{
    lblStarFirstName.Visibility = Visibility.Visible;
}

if (rbMale.IsChecked == false && rbFemale.IsChecked == false)
{
    lblStarGender.Visibility = Visibility.Visible;
}

if (tbDOB.Text == "")
{
    lblStarDOB.Visibility = Visibility.Visible;
}

if (tbDateOfJoining.Text == "")
{
    lblStarDOJ.Visibility = Visibility.Visible;
}

if (tbEducation.Text.Trim() == "")
{
    lblStarEducation.Visibility = Visibility.Visible;
}

if (tbCNIC.Text.Trim() == "")
{
    lblStarCNIC.Visibility = Visibility.Visible;
}

if (tbSalary.Text.Trim() == "")
{
    lblStarSalary.Visibility = Visibility.Visible;
}

if (tbAddress.Text.Trim() == "")
{
    lblStarAddress.Visibility = Visibility.Visible;
}

if (tbEmail.Text.Trim() == "")
{
    lblStarEmail.Visibility = Visibility.Visible;
}

if (tbContact1.Text.Trim() == "")
{
    lblStarContact.Visibility = Visibility.Visible;
}
else
{
    try
    {
        conn.Open();

        cmd.CommandText = "insert into teacher (tIDCardNum, tFirstName, tLastName,tGender, tDOB, tCNIC, tEducation, tSalary, tJoinedOn, tAddress, tEmail, tContact1, tContact2, tContact3,tStatus) values ('" + tbIDCardNum.Text.Trim() + "' , '" + tbFirstName.Text.Trim() + "' , '" + tbLastName.Text.Trim() + "' , '" + gender + "' , '" + tbDOB.Text + "', '" + tbCNIC.Text + "' , '" + tbEducation.Text + "' , '" + tbSalary.Text.Trim() + "' , '" + tbDateOfJoining.Text.Trim() + "' , '" + tbAddress.Text.Trim() + "', '" + tbEmail.Text + "' , '" + tbContact1.Text + "' , '" + tbContact2.Text + "' , '" + tbContact3.Text + "',1)";

        cmd.Connection = conn;
        cmd.ExecuteNonQuery();

        cmd.Clone();
        conn.Close();

        HideStars();
        Refresh();

        MessageBox.Show("Saved");
   }
   catch (Exception ex)
   {
       if (ex.Message.Contains("Violation of PRIMARY KEY constraint "))
       {
           conn.Close();
           MessageBox.Show(ex.Message);
       }
       else
       {
           MessageBox.Show(ex.Message);
       }
   }
}

Answer 1

据我了解，主要问题似乎是您检查了不同 if 语句中的所有字段，但只有最后一个有 else。正如我从您的帖子中假设的那样，这是您的问题；您希望每个文本框在开始将其插入数据库之前都有一个值，对吗？

如果将您的代码分解成更可重用的东西，顺便清理一下东西，这会更好地解释。

首先，首先在您的类中引入一个变量，我们可以用它来查看是否有任何空字段:

private bool HasEmptyFields = false;

接下来，让我们创建一个简单的助手来检查文本框是否为空/空，更新相应标签的可见性状态，如果它确实为空，则将 'HasEmptyFields' 设置为 true:

private void ValidateField(TextBox textBox, Label label) {

    // check if the textbox actually is null - or empty (""), which is a difference
    // the nifty helper string.IsNullOrEmpty() will help with that
    var fieldIsEmpty = string.IsNullOrEmpty(textBox.Text.Trim());

    // next, based on if the field is empty,  set the visibility of the label
    // don't worry, this is fancy syntax for a simple if...then...else
    label.Visibility = fieldIsEmpty ? Visibility.Visible : Visibility.Hidden;

    if (fieldIsEmpty) {
        // ONLY if this field is actually null, or empty, we make sure to 
        // inform the rest of the code this occ
        HasEmptyFields = true;
    }
}

有了这个，我们可以做类似的事情:

ValidateField(tbIDCardNum, lblStarIDCardNum);
ValidateField(tbFirstName, lblStarFirstName);
// etc... continue doing this for all you fields

if (HasEmptyFields) {
    // ONLY if there is any field detected as being empty/null
    // we simply stop here (and skip the insert-into-db stuff)
    return;
} 

try 
{
    // if all fields indeed have a value, let's
    // continue with the insert-into-db stuff here

    conn.Open();
    ...
} 

现在肯定有办法让它更漂亮。但这可能会帮助您朝着正确的方向前进。同样值得一提的是其他一些评论，比如防止 SQL injection (这肯定会发生)，以及研究数据验证工具，这样您就不必自己编写所有这些验证代码。但这显然不在本答案的范围内。