How do I deal with image datatype in linq.

Question

How do I deal with image datatype in linq. I am trying to add and retrieve images from a DB table and I am getting this error with a straight conversion of my old code. The class that mapps to the image table is expectins a binaary type instead of a byte array

 

Value of type 'System.Data.Linq.Binary' cannot be converted to '1-dimensional array of Byte

 

If Not (image Is Nothing AndAlso image.imageId > 0) Then

context.Response.Clear()

context.Response.BufferOutput = False

context.Response.OutputStream.Write(CType(image.imageData, Byte()), 0, CInt(image.imageSize))

context.Response.End()

End If

 

Answer 1

You can change the mapping to have the property be 'byte[]' instead of 'Binary'.  There are advantages to having 'Binary' though.  You can also get a 'byte[]' from a 'Binary' using 'binary.ToArray()'.

 

 

 

Answer 2

Hi,

 

In my first attempt (using Northwind.Employee.Photo column) I kept getting the following exception:

System.ArgumentException was unhandled
  Message="Parameter is not valid."
  Source="System.Drawing"
  StackTrace:
       at System.Drawing.Bitmap..ctor(Stream stream)
       at LinqPOC.Program.Q1() in D:\Users\Ben Hall\Documents\Visual Studio 2008\Projects\LinqPOC\LinqPOC\Class1.cs:line 37
       at LinqPOC.Program.Main(String[] args) in D:\Users\Ben Hall\Documents\Visual Studio 2008\Projects\LinqPOC\LinqPOC\Class1.cs:line 19
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

The code:

Code Block

MemoryStream ms = new MemoryStream(item.Photo.ToArray());

Bitmap bmp = new Bitmap(ms);

bmp.Save(Path.GetTempFileName());

 

 

Turns out Northwind is a bit strange and includes the header - http://www.akadia.com/services/dotnet_load_blob.html

Changed the code to this:

Code Block

Byte[] img = item.Photo.ToArray();

MemoryStream ms = new MemoryStream();

//http://www.akadia.com/services/dotnet_load_blob.html

int offset = 78;

ms.Write(img, offset, img.Length - offset);

Bitmap bmp = new Bitmap(ms);

string path = Path.GetTempFileName();

Console.WriteLine(path);

bmp.Save(path);

 

 

This just removes the header,  this then works fine.

 

Hope this helps you.

 

Ben

Answer 3

Hullo Matt Warren

 am using Asp.net 3.5, Visual Studio 2008. I upload some files(image,text file) to image datatype column as binary format using LINQ , now i want to retrieve those files, i have write the following code

 

            ArrayList alFileContent = new ArrayList();
            ArrayList alFileFormat = new ArrayList();
            ArrayList alFileSize = new ArrayList();
            string datatype1 = "System.String"; string datatype2 = "System.Byte[]";
            string datatype3 = "System.String"; string datatype4 = "System.Int64";
            DataContext dc = new DataContext(Convert.ToString(Session["LINQConnectionString"]));
            DataTable dt = new DataTable();

            dc.Connection.Open();
           
            DataColumn dc_filename = new DataColumn(Convert.ToString(Session["FileNameColumnName"]));
            dc_filename.DataType = System.Type.GetType(datatype1);
            dt.Columns.Add(dc_filename);

            DataColumn dc_filecontent = new DataColumn(Convert.ToString(Session["FileContentColumnName"]));
            dc_filecontent.DataType = System.Type.GetType(datatype2);
            dt.Columns.Add(dc_filecontent);

            DataColumn dc_fileformat = new DataColumn(Convert.ToString(Session["FormatColumnName"]));
            dc_fileformat.DataType = System.Type.GetType(datatype3);
            dt.Columns.Add(dc_fileformat);

            DataColumn dc_filesize = new DataColumn(Convert.ToString(Session["FileSizeColumnName"]));
            dc_filesize.DataType = System.Type.GetType(datatype4);
            dt.Columns.Add(dc_filesize);

            var SelectQueryForFileName = dc.ExecuteQuery<string>(Convert.ToString(Session["PassQueryToImageGrabForFileName"]));
            var SelectQueryForFileFormat = dc.ExecuteQuery<string>(Convert.ToString(Session["PassQueryToImageGrabForFileFormat"]));

          // BELOW LINE IS MY PROBLEM
            var SelectQueryForFileContent = dc.ExecuteQuery<byte>("Select file_content from FILE_MASTER");

 

when the above line is reached then i got the error as specified cast is not valid . i understand this occur due to datatype conversion, but how can i read the binary data from table. If i use byte[] then it return an error message as

The type 'System.Byte[]' must declare a default (parameterless) constructor in order to be constructed during mapping

 

                                    Please anybody answer me . Thank you.

Answer 4

 

http://support.microsoft.com/kb/317034/en-us

Answer 5

I found it looks like a microsoft bug, i read this in the following folder

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=697469&SiteID=1