從列表中獲取請求的列不同值

Question

我有一個包含多個列的列表。我想根據請求的列名稱（列名稱將作爲參數）篩選具有不同值的列表。

IList<obj1> objTemp= new List<obj1>(); 
for (int i = 0; i < 15; i++) 
{ 
    obj1 temp= new obj1(); 
    temp.Name = "Name" + i; 
    temp.Age= "Age" + i; 
    temp.Company= "Company" + i; 
    objTemp.Add(temp); 
} 

var distinctTypeIDs = objTemp.Select(x => x.**{my requested column}**).Distinct(); 

Answer 1

您可以使用反射由它的名字獲得所需屬性：

var distinctTypeIDs = objTemp.Select(x => x.GetType().GetProperty("requested_column").GetValue(x)) 
          .Distinct(); 

Answer 2

一種方法是使用這樣的方法。

private IList<obj1> SortListAccordingToParameter(string filter) 
{ 
if(filter == "Name") 
    return objTemp.Select(x => x.Name).Distinct(); 
else if(filter == "Age") 
    return objTemp.Select(x => x.Age).Distinct(); 
else if(filter == "Company") 
    return objTemp.Select(x => x.Company).Distinct(); 
} 

Answer 3

如果您知道要搜索的屬性的類型，則可以使用表達式。

string propName = "Age"; 
var paramExpression = Expression.Parameter(typeof(Obj1)); 
// o => 

var memberExpression = Expression.Property(paramExpression, propName); 
// o => o.Age 

var lambdaExpression = Expression.Lambda<Func<Obj1, string>>(memberExpression, paramExpression); 
// (o => o.Age) 

var compiled = lambdaExpression.Compile(); 

IList<Obj1> objTemp = new List<Obj1>(); 
for (var i = 0; i < 15; i++) { 
    Obj1 temp = new Obj1(); 
    temp.Name = "Name" + i; 
    temp.Age = "Age" + i; 
    temp.Company = "Company" + i; 
    objTemp.Add(temp); 
} 

var results = objTemp.Select(compiled); 
// equivalent to objTemp.Select(o => o.Age), plus a delegate call and the time to 
// compile the lambda. 

我可能會在一個靜態類包裝這件事，像這樣：

static class Gen<TModel, TProp> { 
    public static Func<TModel, TProp> SelectorExpr(string propertyName) { 
     var pExpr = Expression.Parameter(typeof (TModel)); 
     var mExpr = Expression.Property(pExpr, propertyName); 
     var lExpr = Expression.Lambda<Func<TModel, TProp>>(mExpr, pExpr); 
     return lExpr.Compile(); 
    } 
} 

這樣你可以寫你的選擇，如：

var results = objTemp.Select(Gen<Obj1, string>.SelectorExpr(propName)); 

這似乎更加清晰一點對我來說，我正在做什麼，特別是如果我正在閱讀表達DOM代碼，我寫了6個月後。

Answer 4

我一直是「映射」列的風扇負責檢索該列的內容的匿名方法：

using System; 
using System.Collections.Generic; 
using System.Linq; 

public class Program 
{ 
    public static void Main() 
    { 
     Console.WriteLine("Hello World"); 
     var items = new List<SomeObject> {new SomeObject { Age = 10, Name = "Daniel", Company = "InCycle" }, 
             {new SomeObject { Age = 20, Name = "Not Daniel", Company = "Not InCycle" } 
             }}; 

     var result = Filter<int>(items, "Age"); 
     Console.WriteLine(result.Last()); 

    } 

    public static IEnumerable<T> Filter<T>(IEnumerable<SomeObject> items, string filterCriteria) 
    { 
     var mappings = new Dictionary<string, Func<IEnumerable<SomeObject>, IEnumerable<T>>> 
     { 
      { "Age", filterItems => filterItems.Select(item => item.Age).Distinct().Cast<T>() }, 
      { "Name", filterItems => filterItems.Select(item => item.Name).Distinct().Cast<T>() }, 
      { "Company", filterItems => filterItems.Select(item => item.Company).Distinct().Cast<T>() } 
     }; 

     return mappings[filterCriteria](items); 

    } 
} 

public class SomeObject 
{ 
    public int Age {get;set;} 
    public string Name {get;set;} 
    public string Company {get; set;} 
} 

對這個缺點的做法是，如果添加額外的屬性，你可以忘記將它們添加到過濾。表達式也是一種可靠的方法。

Answer 5

public class Test 
{ 
    public string name { get; set; } 
    public string age { get; set; } 
    public string contact { get; set; } 

    public Test getName(string name) 
    { 
     List<Test> testList = new List<Test>(); 

     testList.Add(new Test { name = "Developer", age = "24", contact = "99009900990" }); 
     testList.Add(new Test { name = "Tester", age = "30", contact = "009900990099" }); 

     return testList.Where(c => c.name == name).FirstOrDefault(); 
    } 
    } 
    static void Main(string[] args) 
    { 
     Test testObj = new Test(); 
     Test selectedObj = testObj.getName("Developer"); 
    }