EF修改部分字段

/// <summary>
/// 修改
/// </summary>
/// <param name="bookinfo"></param>
/// <returns></returns>
public static bool update(bookinfo bookinfo)
{
using (bookdbcontext db = new bookdbcontext())
{
//将实体附加到上下文中
db.bookinfo.attach(bookinfo);

db.entry<bookinfo>(bookinfo).property(p => p.unitprice).ismodified = true;//更新指定的字段

int num = db.savechanges();
if (num > 0)
{
return true;
}
else
{
return false;
}

}
}