UniBlob Class

In This Topic

Represents a variable-length stream of binary data to be stored in or retrieved from a database.

Syntax

Visual Basic
C#

'Declaration
 
Public Class UniBlob 
   Implements System.IDisposable

public class UniBlob : System.IDisposable

Remarks

UniBlob is used to insert or retrieve BLOB fields in databases.

See article Working with BLOB Data for detailed information.

Example

In this example two functions are presented. First can upload a file onto a server, and second can retrieve a BLOB field and paste it into a file. Notice that two classes used here (BinaryWriter and BinaryReader) to provide more flexible stream manipulation are actually redundant for simple data transfer operations.

csharp

public void DownloadBlob(UniConnection myConnection)
{
  UniCommand myCommand = new UniCommand("SELECT * FROM Test.Pictures", myConnection);
  myConnection.Open();
  UniDataReader myReader = myCommand.ExecuteReader(System.Data.CommandBehavior.Default);
  try
  {
    while (myReader.Read())
    {
      UniBlob myBlob = myReader.GetUniBlob(myReader.GetOrdinal("Picture"));
      if(!myBlob.IsNull)
      {
        string FN = myReader.GetString(myReader.GetOrdinal("PicName"));
        FileStream fs = new FileStream("D:\\Tmp\\"+FN+".bmp", FileMode.Create);
        BinaryWriter w = new BinaryWriter(fs);
        w.Write(myBlob.Value);
        w.Close();
        fs.Close();
        Console.WriteLine(FN+" downloaded.");
      }
    }
  }
  finally
  {
    myReader.Close();
    myConnection.Close();
  }
}                                                                                                                   

public void UploadBlob(UniConnection myConnection)
{
  FileStream fs = new FileStream("D:\\Tmp\\_Water.bmp", FileMode.Open, FileAccess.Read);
  BinaryReader r = new BinaryReader(fs);
  UniBlob myBlob = new UniBlob(r.ReadBytes((int)fs.Length));
  UniCommand myCommand = new UniCommand("INSERT INTO Test.Pictures (ID, PicName, Picture) VALUES(1,'Water',:Pictures)", myConnection);
  myCommand.Parameters.Add("Pictures",myBlob);
  myConnection.Open();
  try
  {
    Console.WriteLine(myCommand.ExecuteNonQuery()+" rows affected.");
  }
  finally
  {
    myConnection.Close();
    r.Close();
  }
}

Visual Basic

Public Sub DownloadBlob(ByVal myConnection As UniConnection)
  Dim myCommand As New UniCommand("SELECT * FROM Test.Pictures", myConnection)
  myConnection.Open()
  Dim myReader As UniDataReader = myCommand.ExecuteReader(System.Data.CommandBehavior.Default)
  Try
    While myReader.Read()
      Dim myBlob As UniBlob = myReader.GetUniBlob(myReader.GetOrdinal("Picture"))
      If Not myBlob.IsNull Then
        Dim FN As String = myReader.GetString(myReader.GetOrdinal("PicName"))
        Dim fs As FileStream = New FileStream("D:\Tmp\" + FN + ".bmp", FileMode.Create)
        Dim w As BinaryWriter = New BinaryWriter(fs)
        w.Write(myBlob.Value)
        w.Close()
        fs.Close()
        Console.WriteLine(String.Concat(FN, " downloaded."))
      End If
    End While
  Finally
    myReader.Close()
    myConnection.Close()
  End Try
End Sub

Public Sub UploadBlob(ByVal myConnection As UniConnection)
  Dim fs As FileStream = New FileStream("D:\Tmp\_Water.bmp", FileMode.Open, FileAccess.Read)
  Dim r As BinaryReader = New BinaryReader(fs)
  Dim myBlob As UniBlob = New UniBlob(r.ReadBytes(Convert.ToInt32(fs.Length)))
  Dim myCommand As UniCommand = New UniCommand("INSERT INTO Test.Pictures (ID, PicName, Picture) VALUES(2,'Water',:Pictures)", myConnection)
  myCommand.Parameters.Add("Pictures", myBlob)
  myConnection.Open()
  Try
    Console.WriteLine(String.Concat(myCommand.ExecuteNonQuery(), " rows affected."))
  Finally
    myConnection.Close()
    r.Close()
  End Try
End Sub

Inheritance Hierarchy

System.Object
Devart.Data.Universal.UniBlob

Reference

UniBlob Members
Devart.Data.Universal Namespace

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