[Linq]動態組合Linq條件

以前寫Linq的時候常常碰到一個問題,就是判斷一個條件是否達成來決定Linq的Where條件該如何組合,
例如:

void Main()
{
 bool Flag = true;
 List<DealDataForGov> SourceData = new List<DealDataForGov>
 {
  new DealDataForGov
  {
   Address = "台北市xxxx",
   HouseKind = "a1",
   Year = 2015
  },
  new DealDataForGov
  {
   Address = "高雄市xxxx",
   HouseKind = "a1",
   Year = 2016
  },
  new DealDataForGov
  {
   Address = "台中市xxxx",
   HouseKind = "c1",
   Year = 2014
  }
 }

 if (Flag)
 {
  SourceData.Where((x) => x.HouseKind == "a1");
 }
 else 
 {
  //因為某個條件,新增新的搜尋條件
  SourceData.Where((x) => x.HouseKind =="a1" && x.Year >= 2015 );
 }
}

public class DealDataForGov
{
 public string Address { get; set; }
 public string HouseKind { get; set; }
 public int Year {get;set;}
}

條件少還算好寫，一旦條件落落長的時候就會貼的到處都是，不僅彈性降低也讓維護增加困難度，還好在黑大那邊看到LINQKIT這個好東西黑暗執行緒-組裝動態LINQ條件的利器－LINQKit

以下簡短介紹一下這個LINQKit的套件，有了他之後感覺Code都活過來了XD
範例:

void Main()
{
 List<TargetModel> SourceData = new List<TargetModel>
 {
  new TargetModel
  {
   Address = "台北市xxxx",
   HouseKind = "a1",
   Year = 2015
  },
  new TargetModel
  {
   Address = "高雄市xxxx",
   HouseKind = "a1",
   Year = 2016
  },
  new TargetModel
  {
   Address = "台中市xxxx",
   HouseKind = "c1",
   Year = 2014
  }
 };

 var expression = GetWhereExpression();

 //SourceData.Where((x) => x.HouseKind == "a1");
 var e1 = SourceData.Where(expression.Compile());
 e1.Dump();

 //SourceData.Where((x) => x.HouseKind =="a1" && x.Year > 2015 );
 var e2 = SourceData.Where(expression.And(x => x.Year > 2015).Compile());
 e2.Dump();

 //SourceData.Where((x) => x.HouseKind =="a1" || x.Year >=2014 );
 var e3 = SourceData.Where(expression.Or(x => x.Year >= 2014).Compile());
 e3.Dump();
}

public Expression<Func<TargetModel, bool>> GetWhereExpression()
{
 var pred = PredicateBuilder.True<TargetModel>();
  pred = pred.And(x=> x.HouseKind =="a1");
  return pred;
}

public class TargetModel
{
 public string Address { get; set; }
 public string HouseKind { get; set; }
 public int Year {get;set;}
}

上面有三個範例分別是替代掉註解的寫法,如果有碰到很多條件會動態產生的結果,用LinqKit可以大幅度省掉很多Code以及維護上的複雜度。算是非常好用的小物，推薦給大家