A more complex LINQ statement

As a beginner, it took me a lot of effort to write this sentence. It is secondary to write it out. What is important is that I learned a new usage.

VaR query = from GB in objectcontext. goodsclose_back
Where GB. s_sf = comid & GB. s_month = month
Join GW in // subquery similar
(
From GHB in objectcontext. goodsclose_history_caiwu_1
Where GHB. s_month = lastmonth
Join W in objectcontext. waitfinancein_import

 

// Match the new {GHB. s_goodsid, GHB. s_sf, s_month = month} combinations. The names of the fields before and after the match must be the same.
On New {GHB. s_goodsid, GHB. s_sf, s_month = month} equals New {W. s_goodsid, W. s_sf, s_month = W. s_month} into T // left join. If defaultifempty () is not used here, it is equivalent to the number of rows on the right of the data on the left, which exist as a set, when this function is used, the data on the right is split up several times to repeat the data on the left to correspond to the data on the right.
Select New // goodsclosefinancebackpm
{

 

// Here s_goodsid, s_sf, and s_month are used for the following purposes. If this parameter is not set, it will not be called below.
S_goodsid = GHB. s_goodsid,
S_sf = GHB. s_sf,
S_month = month,
Currentwaitinqty = T. sum (x => (X. f_importqty ?? 0)-(X. f_inv_qty ?? 0 )),
Currentwaitinamt = T. sum (x => (X. f_importqty ?? 0) * (X. f_importpri ?? 0)-(X. f_inv_qty ?? 0) * (X. f_importpri ?? 0 )),
Oldcloseqty = GHB. f_closeqty ?? 0,
Oldcloseamt = GHB. f_closeamt ?? 0,
Oldpri = GHB. f_closepri ?? 0,
Oldwaitinqty = GHB. f_current_waitfinanceinqty ?? 0,
Oldwaitinamt = GHB. f_current_waitfinanceinamt ?? 0
}
) On new {GB. s_goodsid, GB. s_sf, GB. s_month} equals New {GW. s_goodsid, GW. s_sf, GW. s_month} into GWT
From GW in GWT. defaultifempty ()
Select New goodsclosefinancebackpm
{
Goodsid = GB. s_goodsid,
Comid = comid,
Month = month,

Closeqty = GB. f_closeqty ?? 0,
Purpri = GB. f_purpri ?? 0,
Inqty = GB. f_inqty ?? 0,
Outqty = GB. f_outqty ?? 0,
Transeinqty = GB. f_transinqty ?? 0,
Transeoutqty = GB. f_transoutqty ?? 0,
Unit = GB. s_unit,
Oldpri = GW. oldpri,
Currentwaitinqty = GW. currentwaitinqty,
Currentwaitinamt = GW. currentwaitinamt,
Oldcloseqty = GW. oldcloseqty,
Oldcloseamt = GW. oldcloseamt,
Oldwaitinqty = GW. oldwaitinqty,
Oldwaitinamt = GW. oldwaitinamt
};