How to insert and retrieve image from PostgreSql using C#

Question

I am trying to insert an image into Postgres and retrieve that image from postgresql using C#.

I have two columns in my table: memberid (character varying) and member_photo (bytea)

Here is my code to insert the image:

using (FileStream pgFileStream = new FileStream("D:\\Capture.jpg", FileMode.Open, FileAccess.Read))
{
    using (BinaryReader pgReader = new BinaryReader(new BufferedStream(pgFileStream)))
    {
        NpgsqlCommand command = new NpgsqlCommand();

        byte[] ImgByteA = pgReader.ReadBytes(Convert.ToInt32(pgFileStream.Length));
        command.CommandText = "insert into membermaster (memberid, member_photo) VALUES ('65', @Image)";
        command.Connection = Program.conn;

        Program.conn.Close();
        Program.conn.Open();

        //command.Parameters.Add(new NpgsqlParameter("Image", ImgByteA));
        command.Parameters.Add("@Image", ImgByteA).Value = ImgByteA;

        command.ExecuteNonQuery();

        Program.conn.Close();
    }
}

Here is my code to retrieve the image

NpgsqlCommand command = new NpgsqlCommand();
command.CommandText = "select member_photo from membermaster where memberid='65'";
command.Connection = Program.conn;

try
{
    Program.conn.Close();
    Program.conn.Open();

    byte[] productImageByte = command.ExecuteScalar() as byte[];

    if (productImageByte != null)
    {
        using (MemoryStream productImageStream = new System.IO.MemoryStream(productImageByte))
        {
            ImageConverter imageConverter = new System.Drawing.ImageConverter();
            pictureBox1.Image = imageConverter.ConvertFrom(productImageByte) as System.Drawing.Image;
            // image.Save(imageFullPath, System.Drawing.Imaging.ImageFormat.Jpeg);

            pictureBox1.Image = System.Drawing.Image.FromStream(productImageStream);
        }
    }
}
catch
{
    Program.conn.Close();
    throw;
}

The code to insert the image is working fine, but I can't show this image in a picturebox.

I get an error:

Parameter is not valid

Please help me solve this problem

Answer 1

AFAIK you cannot retrieve a byte[] using ExecuteScalar. You should use ExecuteReader instead. Just to be on the safe side when inserting parameters, I prefer to specify types myself, so my insert looks like this:

using (var conn = new NpgsqlConnection(connString))
{
    string sQL = "insert into picturetable (id, photo) VALUES(65, @Image)";
    using (var command = new NpgsqlCommand(sQL, conn))
    {
        NpgsqlParameter param = command.CreateParameter();
        param.ParameterName = "@Image";
        param.NpgsqlDbType = NpgsqlTypes.NpgsqlDbType.Bytea;
        param.Value = ImgByteA;
        command.Parameters.Add(param);

        conn.Open();
        command.ExecuteNonQuery();
    }
}

I can then retrieve and load the image like this:

using (var conn = new NpgsqlConnection(connString))
{
    string sQL = "SELECT photo from picturetable WHERE id = 65";
    using (var command = new NpgsqlCommand(sQL, conn))
    {
        byte[] productImageByte = null;
        conn.Open();
        var rdr = command.ExecuteReader();
        if (rdr.Read())
        {
            productImageByte = (byte[])rdr[0];
        }
        rdr.Close();
        if (productImageByte != null)
        {
            using (MemoryStream productImageStream = new System.IO.MemoryStream(productImageByte))
            {
                ImageConverter imageConverter = new System.Drawing.ImageConverter();
                pictureBox1.Image = imageConverter.ConvertFrom(productImageByte) as System.Drawing.Image;
            }
        }
    }
}

I do not know if specifying the datatype on insert makes any difference, so try just retrieving using a Reader first. If that doesn't work, then I suggest changing your insert routine to something like mine.

Please note in my example id is an integer, not a character varying!

Answer 2

While the code in the accepted answer is working, it is not true that you cannot use ExecuteScalar. It might have been an issue in older versions, but using Npgsql 6.0.7 the following works:

 public static async Task<byte[]?> GetByteaAsync(int id, string connectionString) {
    byte[]? result = null;
    await using (var con = new NpgsqlConnection(connectionString)) {
        await con.OpenAsync();
        await using (var cmd = new NpgsqlCommand("SELECT field_name from table_name where id=@id", con) {CommandType = CommandType.Text}) {
            cmd.Parameters.Add("@id", NpgsqlDbType.Integer).Value = id;

            result = ((byte[]?) await cmd.ExecuteScalarAsync());
        }

        await con.CloseAsync();
    }

    return result;
}