In databases, serialization is mainly done to store images. All databases provide the feature to store images. For example:

·         IMAGE data type in MS SQL: It can hold variable length binary data with a maximum length of 2 GB.

·         BLOB, MEDIUMBLOB and LONGBLOB in MySQL: BLOB refers to Binary Large Objects that can store up to 64 KB of data. MEDIUMBLOB can store up to 16 MB and LONGBLOB stores up to 4 GB of binary data. BLOBs can store a variable amount of data.

Let us consider a small table DEMO consisting of 3 columns.

Case I (Uploading image from file)

Serializing and uploading an image on to a database is a three step process.

1.    Create a MemoryStream object from an image file. A MemoryStream class creates a stream in memory instead of a disk. In MemoryStream, data is stored as an unsigned byte array that is directly accessible in memory.

2.    Serialize the MemoryStream into binary format through a BinaryFormatter. BinaryFormatter is the class that is used to serialize and de-serialize any object into a binary stream.

3.    Upload the bytes formed from the MemoryStream to the database. This is achieved by a simple Insert or Update operation that is carried for any other field in the table. The difference is that the image to be uploaded would be an array of bytes.

NOTE: The Listings here are based on MySQL database. The connection and command objects used here belong to the namespace MySql.Data.MySqlClient. This is found from the MySQL .NET Connector which is an ADO.NET driver for MySQL.

The Listing below consists of two functions.

SerializeNSaveToDB()

This function first creates an Image object from a file and serializes it into a MemoryStream. It then calls the Call_Upload_Object() function to save the serialized object to the database.

Call_Upload_Object(string query, byte[] image, string column)

It takes three arguments, the query, an array of bytes that is the serialized object, in this case the image, and the column name (used in the Query). It then performs the necessary database operation with the help of the classes provided by the MySQL .NET Connector.

Listing 1: Serialization of Image from file

using MySql.Data.MySqlClient;
 
private string imagePath = string.Empty;
private string MySqlConnString =
  "Server = localhost; Uid = root; Pwd = password;
Database = demo;";
private void SerializeNSaveToDB()
{
  MemoryStream str = new MemoryStream();
  try
  {
    string column = "?IMAGE ";
    Image img = Image.FromFile(imagePath);
    BinaryFormatter oBFormatter = new BinaryFormatter();
    oBFormatter.Serialize(str, img);
    byte[]oSerializedImg = str.ToArray();
    string Query = "INSERT INTO DEMO (NAME, PHOTO) VALUES('Image 1',  ? IMAGE)
      ";Call_Upload_Object(Query, oSerializedImg, column);
  }
  catch (Exception ex)
  {
    MessageBox.Show(ex.Message);
  }
  finally
  {
    str.Close();
  }
}
 
private void Call_Upload_Object(string query, byte[]image, string column)
{
  MySqlConnection oMySqlConnection = new MySqlConnection(MySqlConnString);
  try
  {
    MySqlCommand oMySqlCommand = new MySqlCommand();
    oMySqlConnection.Open();
    oMySqlCommand.Connection = oMySqlConnection;
    oMySqlCommand.CommandText = query;
    oMySqlCommand.Parameters.Add(column, image);
    oMySqlCommand.ExecuteNonQuery();
  }
  catch (Exception ex)
  {
    throw ex;
  }
  finally
  {
    oMySqlConnection.Close();
  }
}

Case II (Downloading an image from Database)

This is also a three step process.

1.    First, the image is fetched into a byte array and is then converted into a stream like MemoryStream or FileStream.

2.    The stream of bytes is now de-serialized by using a BinaryFormatter.

3.    This Stream is then either written to a file or can be directly displayed in a PictureBox.

Listing 2 consists of a single function.

DeserializeNSaveToFile()

This function fetches the serialized image from the database with the help of MySqlClient Classes. This object is converted into a MemoryStream object which is then de-serialized with the help of a BinaryFormatter. This is in turn converted into an Image and can be easily stored into a file or can be directly displayed by a PictureBox in our application.

Listing 2: De-serialization of Image from Database

private void DeserializeNSaveToFile()
{
  DataTable ds = new DataTable();
  MySqlConnection oMySqlConn = new MySqlConnection(MySqlConnString);
  try
  {
    string Query = "SELECT * FROM DEMO";
    MySqlCommand cmd = new MySqlCommand(Query, oMySqlConn);
    oMySqlConn.Open();
    MySqlDataAdapter da = new MySqlDataAdapter(cmd);
    da.Fill(ds);
    MemoryStream oStr = new MemoryStream((byte[])ds.Rows[0]["PHOTO"]);
    BinaryFormatter oBFormatter = new BinaryFormatter();
    Image img = (Image)oBFormatter.Deserialize(oStr);
    img.Save("C:\\demo_image.jpg", ImageFormat.Jpeg);
  }
  catch (Exception ex)
  {
    MessageBox.Show(ex.Message);
  }
  finally
  {
    oMySqlConn.Close();
  }
}