获取savechangeasync（）的错误？

Question

＆＃39; proEntities＆＃39;不包含＆＃39; SaveChangesAsync＆＃39;的定义没有扩展方法＆＃39; SaveChangesAsync＆＃39;接受第一个类型＆＃39; proEntities＆＃39;可以找到（你错过了使用指令或程序集引用）

    private async void button1_Click(object sender, EventArgs e)
    {
        using (proEntities db = new proEntities())
        {
            mypic prjt = new mypic() { filename = filename ,data = ConvertImageToBinary(pictureBox1.Image)};
            db.mypics.Add(prjt);
            await db.SaveChangesAsync();

            MessageBox.Show("successfully saved.", "message", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
    }

https://i.stack.imgur.com/XWI0o.jpg