C 中Linq常用用法

簡單的交集、並集、差集用法如下：

list<

string
> lista =
newlist
<
string
>()
;list<
string
> listb =
newlist
<
string
>()
;list<
string
> listresult =
newlist
<
string
>()
;listresult = lista.
distinct()
.tolist()
;//去重
listresult = lista.
except
(listb)
.tolist()
;//差集
listresult = lista.
union
(listb)
.tolist()
;//並集
listresult = lista.
intersect
(listb)
.tolist()
;//交集

步驟如下：

(1)先定義model。

public

class
itemmodel
public
string itemname 
}

public

class
itemmodelcomparer
:iequalitycomparer
else
if(object.
referenceequals
(x,null
)|| object.
referenceequals
(y,null))
else
else
}return checkflag;
}//實現獲取雜湊值
public
intgethashcode
(itemmodel model)
}

list lista =

newlist
<
itemmodel
>()
;list listb =
newlist
<
itemmodel
>()
;list listresult =
newlist
<
itemmodel
>()
;listresult = lista.
distinct
(new
itemmodelcomparer()
).tolist()
;//去重
listresult = lista.
except
(listb,
newitemmodelcomparer()
).tolist()
;//差集
listresult = lista.
union
(listb,
newitemmodelcomparer()
).tolist()
;//並集
listresult = lista.
intersect
(listb,
newitemmodelcomparer()
).tolist()
;//交集

int tempsatisfiedconditioncount = (from r1 in whitelist

join r2 in args.diaglist on r1.diagcode equals r2.diagcode
select r1).count();

//多條件的聯合查核

list whitediaglist =
(from r1 in diagcontrollist
where r1.controlrelation ==
1join r2 in args.
diaglist on new
equals new
select r1)
.tolist
<
diagcontrolmodel
>()
;

var leftjoin = from emp in listofemployees

join dept in listofdepartment
on emp.deptid equals dept.id into joinedempdept
from dept in joinedempdept.defaultifempty()
select new
;

1、可以有多個let子句

2、let後的變數無需宣告型別

參見下例：

var query = from a in list  

let b = a.name.split('-') 
let c=a.age 
where b[0] =="zhangs" & c>21 
select a;

var linqtest = from r in db.am_recproscheme

orderby r.rpid descending
group r by r.rectype into n
select new
;

var datalist= (from r in druglabellist

group r by new
into q
let drugamount = q.sum(t => convert.toint32(t.chargeamount))
where drugamount >= 0
select new printdruglabelmodel
).tolist();

var linqtest = (from r in db.am_recproscheme

select r).sum(p => p.rpid);

var linqtest = (from r in db.am_recproscheme

where r.rpid > 10
orderby r.rpid descending //倒序
// orderby r.rpid, r.rpname descending //多條件的倒序（與sql語句中的相同）
// orderby r.rpid ascending //正序
select r);

//如果取最後乙個可以按倒敘排列再取值

var linqtest = (from r in db.am_recproscheme 
select r).firstordefault();

var linqtest = (from r in db.am_recproscheme

where r.rpid > 10
orderby r.rpid descending
select r).skip(10).take(10); //取第11條到第20條資料

//可以使用list、array、string的contains()方法進行判斷

var linqtest = (from r in db.am_recproscheme
where r.sortstext.contains("張")
select r);

var linqtest = (from r in db.am_recproscheme

join w in db.am_test_result on r.rpid equals w.rsid
orderby r.rpid descending
select r);

//遍歷datatable，將其中的資料對應到clientstruct中：  

listlist = (from x in dttable.asenumerable() 
orderby x.field("") descending 
where x.field("errortype") == "漏孔" 
select new clientstruct 
).tolist();

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