C# 与Linq的条件连接
有没有一种方法可以逐步/有条件地向查询添加连接?我正在为客户创建一个自定义报告工具,并向客户提供了一个他/她可以选择查询的对象列表。查询中将始终使用一个基本对象(“FWOBid”) 因此,例如,如果客户选择对象“FWOBid”、“FWOItem”和“FWOSellingOption”,我会这样做:C# 与Linq的条件连接,c#,linq,C#,Linq,有没有一种方法可以逐步/有条件地向查询添加连接?我正在为客户创建一个自定义报告工具,并向客户提供了一个他/她可以选择查询的对象列表。查询中将始终使用一个基本对象(“FWOBid”) 因此,例如,如果客户选择对象“FWOBid”、“FWOItem”和“FWOSellingOption”,我会这样做: var query = from fb in fwoBids // if "FWOSellingOption", add this join join so in sellingOptions on
var query = from fb in fwoBids
// if "FWOSellingOption", add this join
join so in sellingOptions on fb.Id equals so.BidId
// if "FWOItem", add this join
join i in fwoItems on fb.Id equals i.FWOBidSection.BidId
// select "FWOBid", "FWOItem", and "FWOSellingOption" (everything user has selected)
select new { FWOBid = fb, FWOSellingOption = so, FWOItem = i };
诀窍是客户可以选择大约6个彼此相关的对象,从而产生许多不同的连接组合。如果可能的话,我希望避免硬编码 一个选项是结合左连接进行一些自定义连接 一个好的TSQL后端应该不会因为总是使用所有连接而在性能方面有任何缺点,因为如果条件总是false,那么优化程序只会删除连接。但这应该被检查出来
bool joinA = true;
bool joinB = false;
bool joinC = true;
var query = from fb in fwoBids
join so in sellingOptions on new { fb.Id, Select = true } equals new { Id = so.BidId, Select = joinA } into js
from so in js.DefaultIfEmpty()
join i in fwoItems on new { fb.Id, Select = true } equals new { Id = i.FWOBidSection.BidId, Select = joinB } into ji
from i in ji.DefaultIfEmpty()
join c in itemsC on new { fb.Id, Select = true } equals new { Id = c.BidId, Select = joinC }
select new
{
FWOBid = fb,
FWOSellingOption = so,
FWOItem = i,
ItemC = c
};
如果没有真正好的示例问题,很难提供真正好的示例解决方案。然而,我所说的“查询链”是这样的:
var query = from x in dba select new { A = x, B = (B)null, C = (C)null };
if ((joinType & JoinType.B) != 0)
{
query = from x in query
join y in dbb on x.A.Id equals y.Id
select new { A = x.A, B = y, C = x.C };
}
if ((joinType & JoinType.C) != 0)
{
query = from x in query
join y in dbc on x.A.Id equals y.Id
select new { A = x.A, B = x.B, C = y };
}
var query = from x in dba select new { Id = x.Id, Name = x.Name,
TextB = (string)null, TextC = (string)null };
if ((joinType & JoinType.B) != 0)
{
query = from x in query
join y in dbb on x.Id equals y.Id
select new { Id = x.Id, Name = x.Name, TextB = y.Text, TextC = x.TextC };
}
if ((joinType & JoinType.C) != 0)
{
query = from x in query
join y in dbc on x.Id equals y.Id
select new { Id = x.Id, Name = x.Name, TextB = x.TextB, TextC = y.Text };
}
也就是说,根据适当的条件,使用另一个联接查询先前的结果。请注意,要成功执行此操作,每个查询必须生成相同的类型。否则,无法将新查询分配给前一个查询结果变量
请注意,在上面的示例中,我只是为每个可能的输入类型提供了一个单独的属性,相反,我可以让该类型为输入列提供属性,Id
,Name
,然后是B
和C
类型中的Text
属性(必须在查询结果类型中使用不同的名称,例如TextB
和TextC
)。如下所示:
var query = from x in dba select new { A = x, B = (B)null, C = (C)null };
if ((joinType & JoinType.B) != 0)
{
query = from x in query
join y in dbb on x.A.Id equals y.Id
select new { A = x.A, B = y, C = x.C };
}
if ((joinType & JoinType.C) != 0)
{
query = from x in query
join y in dbc on x.A.Id equals y.Id
select new { A = x.A, B = x.B, C = y };
}
var query = from x in dba select new { Id = x.Id, Name = x.Name,
TextB = (string)null, TextC = (string)null };
if ((joinType & JoinType.B) != 0)
{
query = from x in query
join y in dbb on x.Id equals y.Id
select new { Id = x.Id, Name = x.Name, TextB = y.Text, TextC = x.TextC };
}
if ((joinType & JoinType.C) != 0)
{
query = from x in query
join y in dbc on x.Id equals y.Id
select new { Id = x.Id, Name = x.Name, TextB = x.TextB, TextC = y.Text };
}
下面是一个完整的代码示例,在可运行程序中包含上述逻辑:
class A
{
public string Name { get; private set; }
public int Id { get; private set; }
public A(string name, int id)
{
Name = name;
Id = id;
}
public override string ToString()
{
return "{" + Name + ", " + Id + "}";
}
}
class B
{
public int Id { get; private set; }
public string Text { get; private set; }
public B(int id, string text)
{
Id = id;
Text = text;
}
public override string ToString()
{
return "{" + Id + ", " + Text + "}";
}
}
class C
{
public int Id { get; private set; }
public string Text { get; private set; }
public C(int id, string text)
{
Id = id;
Text = text;
}
public override string ToString()
{
return "{" + Id + ", " + Text + "}";
}
}
[Flags]
enum JoinType
{
None = 0,
B = 1,
C = 2,
BC = 3
}
class Program
{
static void Main(string[] args)
{
A[] dba =
{
new A("A1", 1),
new A("A2", 2),
new A("A3", 3)
};
B[] dbb =
{
new B(1, "B1"),
new B(2, "B2"),
new B(3, "B3")
};
C[] dbc =
{
new C(1, "C1"),
new C(2, "C2"),
new C(3, "C3")
};
JoinType joinType;
while ((joinType = _PromptJoinType()) != JoinType.None)
{
var query = from x in dba select new { A = x, B = (B)null, C = (C)null };
if ((joinType & JoinType.B) != 0)
{
query = from x in query
join y in dbb on x.A.Id equals y.Id
select new { A = x.A, B = y, C = x.C };
}
if ((joinType & JoinType.C) != 0)
{
query = from x in query
join y in dbc on x.A.Id equals y.Id
select new { A = x.A, B = x.B, C = y };
}
foreach (var item in query)
{
Console.WriteLine(item);
}
Console.WriteLine();
}
}
private static JoinType _PromptJoinType()
{
JoinType? joinType = null;
do
{
Console.Write("Join type ['A' for all, 'B', 'C', or 'N' for none]");
ConsoleKeyInfo key = Console.ReadKey();
Console.WriteLine();
switch (key.Key)
{
case ConsoleKey.A:
joinType = JoinType.BC;
break;
case ConsoleKey.B:
joinType = JoinType.B;
break;
case ConsoleKey.C:
joinType = JoinType.C;
break;
case ConsoleKey.N:
joinType = JoinType.None;
break;
default:
break;
}
} while (joinType == null);
return joinType.Value;
}
}
在Linq查询语法中,这是不可能的,或者查看其他答案几乎不可读。可读性不强,但另一种可能是使用扩展方法(类似于伪代码):
bool条件1;
布尔条件2;
列表出价=新列表();
List sellingOptions=新列表();
列表项=新列表();
var result=bids.Select(x=>new{bid=x,sellingOption=(sellingOption)null,item=(item)null});
如果(条件1)
result=result.Join(
销售选项,
x=>x.bid.Id,
x=>x.BidId,
(x,sellingOption)=>new{x.bid,sellingOption,item=(item)null});
如果(条件2)
result=result.Join(
项目,
x=>x.bid.Id,
x=>x.BidId,
(x,项目)=>新的{x.bid,x.sellingOption,项目});
这只是一个概念,本质上和彼得·杜尼霍一样
问题是,如果你不想在没有必要的情况下立即加入所有选项,那么它看起来就不那么好了。也许你应该尝试现在加入所有选项,而不必担心性能。你有没有衡量过它可能有多慢或多快?可以将其视为“我现在不需要它!”。如果性能确实是一个问题,那么你可以采取行动。但如果不是,并且你不知道自己是否从未尝试过,那么就按照你提到的六个连接来处理。我希望这是对以前答案的改进
public class Bids
{
public int Id { get; set; }
public double Price { get; set; }
}
public class BidSection
{
public int BidId { get; set; }
}
public class SellingOptions
{
public int BidId { get; set; }
public int Quantity { get; set; }
}
public class Item
{
public int ItemId { get; set; }
public BidSection FWOBidSection { get; set; }
}
public class ConditionalJoin
{
public bool jOpt1 { get; set; }
public bool jOpt2 { get; set; }
public ConditionalJoin(bool _joinOption1, bool _joinOption2)
{
jOpt1 = _joinOption1;
jOpt2 = _joinOption2;
}
public class FBandSo
{
public Bids FWOBids { get; set; }
public SellingOptions FWOSellingOptions { get; set; }
}
public class FBandI
{
public Bids FWOBids { get; set; }
public Item FWOItem { get; set; }
}
public void Run()
{
var fwoBids = new List<Bids>();
var sellingOptions = new List<SellingOptions>();
var fwoItems = new List<Item>();
fwoBids.Add(new Bids() { Id = 1, Price = 1.5 });
sellingOptions.Add(new SellingOptions() { BidId = 1, Quantity = 2 });
fwoItems.Add(new Item() { ItemId = 10, FWOBidSection = new BidSection() { BidId = 1 } });
IQueryable<Bids> fb = fwoBids.AsQueryable();
IQueryable<SellingOptions> so = sellingOptions.AsQueryable();
IQueryable<Item> i = fwoItems.AsQueryable();
IQueryable<FBandSo> FBandSo = null;
IQueryable<FBandI> FBandI = null;
if (jOpt1)
{
FBandSo = from f in fb
join s in so on f.Id equals s.BidId
select new FBandSo()
{
FWOBids = f,
FWOSellingOptions = s
};
}
if (jOpt2)
{
FBandI = from f in fb
join y in i on f.Id equals y.FWOBidSection.BidId
select new FBandI()
{
FWOBids = f,
FWOItem = y
};
}
if (jOpt1 && jOpt2)
{
var query = from j1 in FBandSo
join j2 in FBandI
on j1.FWOBids.Id equals j2.FWOItem.FWOBidSection.BidId
select new
{
FWOBids = j1.FWOBids,
FWOSellingOptions = j1.FWOSellingOptions,
FWOItems = j2.FWOItem
};
}
}
}
公共类投标
{
公共int Id{get;set;}
公共双价{get;set;}
}
公开课投标组
{
public int BidId{get;set;}
}
公共类销售选项
{
public int BidId{get;set;}
公共整数数量{get;set;}
}
公共类项目
{
公共int ItemId{get;set;}
公共BidSection fObjidSection{get;set;}
}
公共类条件连接
{
公共bool jOpt1{get;set;}
公共bool jOpt2{get;set;}
公共条件连接(bool_joinOption1,bool_joinOption2)
{
jOpt1=_joinOption1;
jOpt2=_joinOption2;
}
公营班车
{
公开出价FWOBids{get;set;}
公开出售选项FWOSellingOptions{get;set;}
}
公共类FBandI
{
公开出价FWOBids{get;set;}
公共项FWOItem{get;set;}
}
公开募捐
{
var fwoBids=新列表();
var sellingOptions=新列表();
var fwoItems=新列表();
Add(新出价(){Id=1,Price=1.5});
添加(新的sellingOptions(){BidId=1,Quantity=2});
Add(new Item(){ItemId=10,FWOBidSection=new BidSection(){BidId=1}});
IQueryable fb=fwoBids.AsQueryable();
IQueryable so=sellingOptions.AsQueryable();
IQueryable i=fwoItems.AsQueryable();
IQueryable FBandSo=null;
IQueryable FBandI=null;
if(jOpt1)
{
FBandSo=从fb中的f开始
按f.Id等于s.BidId的顺序加入s
选择新FBandSo()
{
FWOBids=f,
fvosellingoptions=s
};
}
if(jOpt2)
{
FBandI=从fb中的f开始
在f上的i中加入y。Id等于y.fvobidSection.BidId
选择新FBandI()
{
FWOBids=f,
FWOItem=y
};
}
if(jOpt1和&jOpt2)
{
var query=来自FBandSo中的j1
在FBandI中加入j2
在j1.FWOBids.Id上等于j2.FWOItem.FWOBidSection.BidId
选择新的
{
FWOBids=j1.FWOBids,
fvosellingoptions=j1.fvosellingoptions,
FWOItems=j2.FWOItem
};
}
}
}
为什么不呢