DBNull question, ask "everyone"!

ulysses24

string filename = "";
Ranch
if (myFile.PostedFile.ContentLength> 0)
{
  string NM = myFile.PostedFile.FileName;
  int i = NM.LastIndexOf (".");
  string extNM = NM.Substring (i);
  filename = "QC" + mid + extNM;
  UploadFile (filename);
}
else
{
  filename = attachmentLb.Text; // this
}

...

SqlParameter YeWuAttachment = new SqlParameter ("@ YeWuAttachment", SqlDbType.VarChar);
YeWuAttachment.Value = (filename == string.Empty? DBNull.Value: filename);
...

Why does the above code go wrong and how can I fix it? thank you all!

error:
CSSModify.cs (233,56): error CS0173: Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string'

shenmue024

YeWuAttachment.Value = (filename == string.Empty? DBNull.Value: filename);
==>

YeWuAttachment.Value = (filename == string.Empty? DBNull.Value: (object) filename);

wy2400

? : The type of the last two values ​​of the operator must be the same

ulysses24

Oh, I see!

But again:

CSSHandle.cs (1007,6): error CS0266: Cannot implicitly convert type 'object' to 'string'. An explicit conversion exists (are you missing a cast?)

shenmue024

try:

if (filename == String.Empty)
{
YeWuAttachment.Value = DBNull.value;
} else
{
YeWuAttachment.Value = filename;

}

ulysses24

It is possible to separate.
But it's not enough to simplify that way, I can't figure it out!

Therefore, there is only the above question!
What is the reason?

shenmue024

It is possible to separate.
But it's not enough to simplify that way, I can't figure it out!

Therefore, there is only the above question!
What is the reason?
==============
1. ? A: B. The types of A and B must be the same.
 I started to change the type of B to object, this sentence passed,

But it is inconsistent with the Varchar type of the parameter.

So it is written separately.

ulysses24

Thank you!