如何在C#中比较Blob字段的空值 [英] how to compare the null value of a blob field in C#

问题描述

你好，

我在C#中使用mysql.我将图像文件存储到具有BLOB数据类型的mysql中.
但是，每当我从该字段中检索值时，我都想检查它是否为NULL.我该怎么办?

类似于下面的代码.它不起作用.

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.

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;
}

推荐答案

您无法针对System.DBNull进行测试-这是一个类.请使用System.DBNull.Value，或尝试以下操作:

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

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);
    }

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