如何动态地选择从LINQ查询两个字段，结果

Question

如果你有一个简单的LINQ查询，如：

var result = from record in db.Customer 
      select new { Text = record.Name, 
          Value = record.ID.ToString() }; 

它返回一个可映射到一个下拉列表中的对象，是有可能动态指定哪些字段映射到文本和值？

当然，你可以做一个大的情况下（开关）语句，那么每个代码Linq查询分开，但是这是不是很优雅。什么是好的会是这样的：

（伪代码）

var myTextField = db.Customer["Name"]; // Could be an enumeration?? 
var myValueField = db.Customer["ID"]; // Idea: choose the field outside the query 

var result = from record in db.Customer 
      select new { Text = myTextField, 
          Value = myValueField }; 

Answer 1

权的方式来做到这一点是闭包。

Func<Customer, string> myTextField = (Customer c) => c["Name"]; 
Func<Customer, int> myValueField = (Customer c) => c["ID"]; 

var result = from record in db.Customer 
      select new { Text = myTextField(record), 
          Value = myValueField(record) }; 

一个限制是你的myTextField的定义总是需要返回一个字符串。

Answer 2

你可以尝试像

class Customer 
     { 
      public int ID { get; set; } 
      public string Name { get; set; } 
      public string Surname { get; set; } 
     } 

var dict = new Dictionary<string, Func<Customer, string>> 
         { { "ID", (Customer c) => c.ID.ToString() }, 
         { "Name",  (Customer c) => c.Name}, 
         { "Surname", (Customer c) => c.Surname } }; 

      List<Customer> rows = new List<Customer>(); 
      rows.Add(new Customer { ID = 1, Name = "Foo", Surname = "Bar"}); 
      var list = from r in rows 
         select new { Text = dict["ID"](r), Value = dict["Name"](r) }; 

要尝试动态访问属性，你可以尝试像

var dict = new Dictionary<string, Func<Customer, string>> 
      { { "ID", (Customer c) => c.GetType().GetProperty("ID").GetValue(c,null).ToString() }, 
      { "Name",  (Customer c) => c.GetType().GetProperty("Name").GetValue(c,null).ToString()}, 
      { "Surname", (Customer c) => c.GetType().GetProperty("Surname").GetValue(c,null).ToString() } };