MySqlBlob 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 MySqlBlob 
   Inherits System.IO.Stream
   Implements System.Data.SqlTypes.INullable, System.ICloneable, System.IComparable, System.IDisposable, System.Xml.Serialization.IXmlSerializable

public class MySqlBlob : System.IO.Stream, System.Data.SqlTypes.INullable, System.ICloneable, System.IComparable, System.IDisposable, System.Xml.Serialization.IXmlSerializable

Remarks

MySqlBlob is used to insert or retrieve BLOB fields in databases. In MySQL, blob fields are TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB. You can also use MySqlBlob object to access other column types such as TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT, but in this case MySqlText is much more suitable.

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(MySqlConnection myConnection)
{
  MySqlCommand myCommand = new MySqlCommand("SELECT * FROM Test.Pictures", myConnection);
  myConnection.Open();
  MySqlDataReader myReader = myCommand.ExecuteReader(System.Data.CommandBehavior.Default);
  try
  {
    while (myReader.Read())
    {
      MySqlBlob myBlob = myReader.GetMySqlBlob(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(MySqlConnection myConnection)
{
  FileStream fs = new FileStream("D:\\Tmp\\_Water.bmp", FileMode.Open, FileAccess.Read);
  BinaryReader r = new BinaryReader(fs);
  MySqlBlob myBlob = new MySqlBlob(r.ReadBytes((int)fs.Length));
  MySqlCommand myCommand = new MySqlCommand("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 MySqlConnection)
  Dim myCommand As New MySqlCommand("SELECT * FROM Test.Pictures", myConnection)
  myConnection.Open()
  Dim myReader As MySqlDataReader = myCommand.ExecuteReader(System.Data.CommandBehavior.Default)
  Try
    While myReader.Read()
      Dim myBlob As MySqlBlob = myReader.GetMySqlBlob(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 MySqlConnection)
  Dim fs As FileStream = New FileStream("D:\Tmp\_Water.bmp", FileMode.Open, FileAccess.Read)
  Dim r As BinaryReader = New BinaryReader(fs)
  Dim myBlob As MySqlBlob = New MySqlBlob(r.ReadBytes(Convert.ToInt32(fs.Length)))
  Dim myCommand As MySqlCommand = New MySqlCommand("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
   System.MarshalByRefObject
      System.IO.Stream
         Devart.Data.MySql.MySqlBlob
            Devart.Data.MySql.MySqlText

Requirements

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

MySqlBlob Members
Devart.Data.MySql Namespace

Send Feedback