如何使用 C# 从 PostgreSql 插入和检索图像

问题描述：

我正在尝试将图像插入 Postgres 并使用 C# 从 postgresql 中检索该图像.

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

我的表中有两列:memberid(字符变化)和 member_photo(bytea)

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

这是我插入图像的代码:

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();
    }
}

这是我检索图像的代码

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;
}

插入图像的代码工作正常，但我无法在图片框中显示此图像.

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

我收到一个错误:

参数无效

请帮我解决这个问题

答

AFAIK 您无法使用 ExecuteScalar 检索 byte[].您应该改用 ExecuteReader.为了在插入参数时安全起见，我更喜欢自己指定类型，所以我的插入看起来像这样:

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();
    }
}

然后我可以像这样检索和加载图像:

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;
            }
        }
    }
}

我不知道在插入时指定数据类型是否有任何区别，因此请先尝试使用 Reader 进行检索.如果这不起作用，那么我建议将您的插入程序更改为类似我的程序.

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.

请注意，在我的示例中，id 是一个整数，而不是一个变化的字符！

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

如何使用 C# 从 PostgreSql 插入和检索图像

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