如何根據模型的屬性進行查詢？

Question

爲了簡便起見，假設我有一個名爲參與者模型像

public class Participant() 
{ 
    public int? ID {get; set;} 
    public string Name {get; set;} 
    public DateTime JoinDate {get; set;} 
    public string Address1 {get; set;} 
    public string City {get; set;} 
    public string County {get; set;} 
} 

public IList<Participant> SearchParticipants(Participant objParticipant) 
{ 
    using (Db.Context()) 
    { 
     //HOW CAN I ACHEIVE THIS? USING EF 
     //WARNING PSEUDO-CODE/MAGIC FUNCTION (SearchMatches) BELOW 

     return Db.Entities<Participant>().SearchMatches(objParticipant); 
    } 
} 

基本上，我並不想構建多個.where(k => k.PropertyName)查詢。我認爲某些PHP MVC框架具有這種功能，傳遞一個填充了某些屬性的對象，並從數據庫中獲取匹配結果的數組（在我們的例子中爲IList）。

Answer 1

您可以使用反射的組合來遍歷您的屬性，並使用dynamic linq來構建Where謂詞。

下面是一個簡單的例子，作爲一個起點/概念驗證。

目前，它採用null作爲值，表明我們不想where子句，但如果你有一個值類型屬性（如int），那麼你可以添加屬性像[FilterIgnore]或東西，檢查是否能循環通過屬性。

創建一個新的控制檯應用程序以及與此替換的Program.cs然後從樣品添加到項目動態LINQ文件：

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

class MyObject 
{ 
    // Some properties 
    public string PropertyA { get; set; } 
    public string PropertyB { get; set; } 
    public DateTime? PropertyC { get; set; } 

    static void Main(string[] args) 
    { 
     // Our repository 
     var list = new List<MyObject>() { 
       new MyObject() { PropertyA = "test"} , 
       new MyObject() { PropertyB = "test"} , 
       new MyObject() { PropertyC = DateTime.Today} , 
       new MyObject() { PropertyC = DateTime.Today, 
           PropertyA = "test"} 
      }; 

     // Loop through the filtered results 
     // (calling our GetByExample method with a 
     // new object with a property set) 
     foreach (var obj in 
       GetByExample(list, 
           new MyObject() { PropertyC = DateTime.Today })) 
     { 
      // Write some output so we can see it working 
      Console.WriteLine("Found object"); 
      Console.WriteLine(obj.PropertyA); 
      Console.WriteLine(obj.PropertyB); 
      Console.WriteLine(obj.PropertyC); 
     } 

     // Wait for the user to press a key before we close 
     Console.ReadKey(); 
    } 

    static IQueryable<MyObject> GetByExample(List<MyObject> objects, 
              MyObject filterObj) 
    { 
     // Create our query variable that we'll add to 
     var filteredObjects = objects.AsQueryable(); 

     // Loop through each property on this object 
     foreach (var prop in filterObj.GetType().GetProperties()) 
     { 
      // Get the value of this property 
      var propVal = prop.GetValue(filterObj, null); 

      if (propVal != null) 
      { 
       // If the property isn't null add a where clause 
       filteredObjects = 
        filteredObjects.Where(string.Format("{0} = @0", 
                 prop.Name), 
              propVal); 
      } 
     } 

     return filteredObjects; 
    } 
}