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Devart.Data.PostgreSql Namespace / PgSqlBlob Class
Members Example

In This Topic
    PgSqlBlob Class
    In This Topic
    Represents a variable-length stream of binary data to be stored in or retrieved from a database.
    Syntax
    Remarks
    PgSqlBlob is used to insert or retrieve BLOB fields in databases.
    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.

    public void DownloadBlob(PgSqlConnection pgConnection)
    {
      PgSqlCommand pgCommand = new PgSqlCommand("SELECT * FROM Test.Pictures", pgConnection);
      pgConnection.Open();
      PgSqlDataReader myReader = pgCommand.ExecuteReader(System.Data.CommandBehavior.Default);
      try
      {
        while (myReader.Read())
        {
          PgSqlBlob myBlob = myReader.GetPgSqlBlob(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();
        pgConnection.Close();
      }
    }                                                                                                                   
    
    public void UploadBlob(PgSqlConnection pgConnection)
    {
      FileStream fs = new FileStream("D:\\Tmp\\_Water.bmp", FileMode.Open, FileAccess.Read);
      BinaryReader r = new BinaryReader(fs);
      PgSqlBlob myBlob = new PgSqlBlob(r.ReadBytes((int)fs.Length));
      PgSqlCommand pgCommand = new PgSqlCommand("INSERT INTO Test.Pictures (ID, PicName, Picture) VALUES(1,'Water',:Pictures)", pgConnection);
      pgCommand.Parameters.Add("Pictures",myBlob);
      pgConnection.Open();
      try
      {
        Console.WriteLine(pgCommand.ExecuteNonQuery()+" rows affected.");
      }
      finally
      {
        pgConnection.Close();
        r.Close();
      }
    }
    Public Sub DownloadBlob(ByVal pgConnection As PgSqlConnection)
      Dim pgCommand As New PgSqlCommand("SELECT * FROM Test.Pictures", pgConnection)
      pgConnection.Open()
      Dim myReader As PgSqlDataReader = pgCommand.ExecuteReader(System.Data.CommandBehavior.Default)
      Try
        While myReader.Read()
          Dim myBlob As PgSqlBlob = myReader.GetPgSqlBlob(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()
        pgConnection.Close()
      End Try
    End Sub
    
    Public Sub UploadBlob(ByVal pgConnection As PgSqlConnection)
      Dim fs As FileStream = New FileStream("D:\Tmp\_Water.bmp", FileMode.Open, FileAccess.Read)
      Dim r As BinaryReader = New BinaryReader(fs)
      Dim myBlob As PgSqlBlob = New PgSqlBlob(r.ReadBytes(Convert.ToInt32(fs.Length)))
      Dim pgCommand As PgSqlCommand = New PgSqlCommand("INSERT INTO Test.Pictures (ID, PicName, Picture) VALUES(2,'Water',:Pictures)", pgConnection)
      pgCommand.Parameters.Add("Pictures", myBlob)
      pgConnection.Open()
      Try
        Console.WriteLine(String.Concat(pgCommand.ExecuteNonQuery(), " rows affected."))
      Finally
        pgConnection.Close()
        r.Close()
      End Try
    End Sub
    Inheritance Hierarchy

    System.Object
       System.MarshalByRefObject
          System.IO.Stream
             Devart.Data.PostgreSql.PgSqlBlob
                Devart.Data.PostgreSql.PgSqlText

    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

    See Also