how to compare the null value of a blob field in C#

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Hello,

I'm using mysql with c#. I'm storing image files into mysql with BLOB data-type.
But whenever I'm retrieving the value from this field, I want to check whether it's NULL or not. How can I do that?

Something like below code. It's not working.

C#

if ((ds3.Tables["tempEmpDetails"].Rows[0]["Emp_Photo"] != System.DBNull))
{
    Byte[] byteBLOBData = new Byte[0];
    byteBLOBData = (Byte[])(ds3.Tables["tempEmpDetails"].Rows[0]["Emp_Photo"]);
    MemoryStream stmBLOBData = new MemoryStream(byteBLOBData);
    pictureBox2.Image = Image.FromStream(stmBLOBData);
}
else
{
    pictureBox2.Image = Properties.Resources.profile;
}

Posted 11-Mar-11 5:17am

DEB4u

Updated 11-Mar-11 5:23am

HimanshuJoshi

v2

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HimanshuJoshi 11-Mar-11 11:24am

Updated to remove extra PRE tags.

1 solution

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OriginalGriff · Accepted Answer · 2011-03-11T05:35:00

Solution 1

You can't test against System.DBNull - that's a class. Either use System.DBNull.Value, or try this:

C#

object o = ds3.Tables["tempEmpDetails"].Rows[0]["Emp_Photo"];
if (o is System.DBNull))
    {
    pictureBox2.Image = Properties.Resources.profile;
    }
else
    {
    Byte[] byteBLOBData = (Byte[])(o);
    MemoryStream stmBLOBData = new MemoryStream(byteBLOBData);
    pictureBox2.Image = Image.FromStream(stmBLOBData);
    }

Posted 11-Mar-11 5:35am

OriginalGriff

Comments

DEB4u 11-Mar-11 11:41am

can't we write like this?
if (o== System.DBNull)
{
///
}

OriginalGriff 11-Mar-11 14:46pm

No! System.DBNull is not a instance or a variable. It is a class. Would you expect "if (17 == int)" to work?
You can use System.DBNull.Value as I said, if you prefer.
if (o == System.DBNull.Value)
{
...
}
But I find the "is" test easier to read and move obvious.

DEB4u 11-Mar-11 17:42pm

ok..That's working perfectly..Thanx very much

Sergey Alexandrovich Kryukov 11-Mar-11 21:39pm

My 5. And OP needs to understand classes, variables, etc., before getting to databases.
--SA