需要有关连接两个包含周期性事件的表的LINQ查询的帮助

这是一个使用UNION而不是LEFT OUTER的替代答案,它确切地返回了您正在寻找的结果集(我认为我的第一个答案不太符合您的“独特”要求):

var a = from m in month
        join h in holiday on m.Id equals h.MonthId
        select new
        {
            MonthId = m.Id,
            Month = m.Name,
            Holiday = h.Name,
            HolidayDay = h.DayOfMonth,
            Appointment = "",
            AppointmentDay = 0

        };

var b = from m in month
        join p in appointments on m.Id equals p.MonthId
        select new
        {
            MonthId = m.Id,
            Month = m.Name,
            Holiday = "",
            HolidayDay = 0,
            Appointment = p.Description,
            AppointmentDay = p.DayOfMonth
        };

var events = from o in a.Union(b)
            orderby o.MonthId, o.HolidayDay + o.AppointmentDay
            select o;

你需要在SQL中执行左外连接,LINQ看起来像这样(未经测试):

var events =
    from
        m in GetMonths()
    groupjoin
        h in GetHolidays()
        on m.Id equals h.MonthId
        into hol = group
    from
        h in hol.DefaultIfEmpty()
    groupjoin
        a in GetAppointments()
        on m.Id equals a.MonthId
        into appt = group
    from
        a in appt.DefaultIfEmpty()
    where
        //something that narrows all combinations of events to only unique events
    orderby
        m.Id,
        // something that interleaves h.DayOfMonth with m.DayOfMonth
    select
        new
        {
            Month = m.Name,
            Holiday = h.Name,
            HolidayDay = h.DayOfMonth,
            Appointment = a.Description,
            AppointmentDay = a.DayOfMonth
        };