in C#, How can i check image field is null or not?

Question

User-1410946272 posted

Actually i have a table with 7 columns

1) Title  varchar(100)

2)Description varchar(300)

3)ProfilePicture varbinary(max)

4) Image1 varbinary (max)

5)Image2  varbinary(max)

6)Image3 varbinary(max)

7)Image4 varbinary(max)

Image1,2,3,4 are not a mandatory fields so, when i inserted, i check it if it is not there then i insert null value,

 

Now problem is when i retrive them if there is a row contain image1,2 are image content  and 3,4 are null values

dataset also filling as it is in database

but when i checking like

if((byte[])ds.Tables[0].Rows[0]["Image3"] != null

)

it shows error like

Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

so, please tell me how to check if the field is null or not.

Answer 1

User1281381861 posted

Hi,

Please check for same: http://forums.asp.net/t/1145956.aspx/1?Unable+to+cast+object+of+type+System+DBNull+to+type+System+Byte+ 

Answer 2

User-1501102275 posted

Try this:

if(ds.Tables[0].Rows[0]["Image3"] != DBNull.Value) ...

Answer 3

User3866881 posted

HI：）

To decide whether a column value is Null in SQL, you cannot use general null, because the "null" is quite different from "null" in sql db. In fact, all the columns values taken out of the sql, if you want to check whether they are "null" or not, please use DBNull.Value instead of general "null"：）

However, if you cannot get any row from a sql's select statement, thus you can use null directly not DBNull.Value——Here're two samples:

Sample1：select null：It will return a DBNull.Value in C#. Because it will return a single row with the Null value.

Sample2：select * from xxx where 1=0：This will return a common null value equaling to C#, because it will return no rows.

As to this, since your image rows can be fetched, however the value of the image is Null in SQL, you DBNull.Value is your choice.