如何将where语句发送到在LINQ语句中动态执行的方法？

在下面的示例中， GetFilteredCustomers（）工作正常，因此我可以发送我希望客户姓氏的各种字母。

但是我如何构建GetFilteredCustomersDynamic（），这将使我能够发送一个可以动态包含在LINQ语句中的完整where子句？

using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace TestDynamicLinq2343 { public class Program { static void Main(string[] args) { List customers = Customer.GetCustomers(); //semi-dynamic foreach (var customer in Customer.GetFilteredCustomers(customers, "o")) { Console.WriteLine(customer.LastName); } //fully-dyanmic (can send where clauses) foreach (var customer in Customer.GetFilteredCustomersDynamic(customers, c => c.FirstName.Contains("a"))) { Console.WriteLine(customer.LastName); } Console.ReadLine(); } } public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public string Street { get; set; } public string Location { get; set; } public string ZipCode { get; set; } public static List GetCustomers() { List customers = new List(); customers.Add(new Customer { FirstName = "Jim", LastName = "Jones" }); customers.Add(new Customer { FirstName = "Joe", LastName = "Adams" }); customers.Add(new Customer { FirstName = "Jake", LastName = "Johnson" }); return customers; } public static List GetFilteredCustomers(List customers, string letter) { return (from c in customers where c.LastName.Contains(letter) select c).ToList(); } public static List GetFilteredCustomersDynamic(List customers, Func whereClause) { return (from c in customers where ...whereClause... select c).ToList(); } } } 

回答：

感谢elder_george和arjuns，我让这个例子像这样工作（尽管没有Expression ）：

 using System; using System.Collections.Generic; using System.Linq; namespace TestDynamicLinq2343 { public class Program { static void Main(string[] args) { List customers = Customer.GetCustomers(); Func whereClause = c => c.LastName.Contains("a") && c.FirstName.Contains("J"); foreach (var customer in Customer.GetFilteredCustomers(customers, whereClause)) { Console.WriteLine(customer.LastName); } Console.ReadLine(); } } public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public string Street { get; set; } public string Location { get; set; } public string ZipCode { get; set; } public static List GetCustomers() { List customers = new List(); customers.Add(new Customer { FirstName = "Jim", LastName = "Jones" }); customers.Add(new Customer { FirstName = "Joe", LastName = "Adams" }); customers.Add(new Customer { FirstName = "Jake", LastName = "Johnson" }); customers.Add(new Customer { FirstName = "Angie", LastName = "Reckar" }); customers.Add(new Customer { FirstName = "Jean-Luc", LastName = "Beaudoir" }); return customers; } public static List GetFilteredCustomers(List customers, Func whereClause) { return customers .Where(whereClause).ToList(); } } } 

Answer 1

您需要将filter表示为Expression> ，而不是Func 。 这样，您可以使用Queryable.Where方法将此filter添加到LINQ表达式树。

编辑：我错了，因为这段代码使用LINQ到对象，其中委托是适当的过滤条件。 我的错。

例如（更正为使用普通代表）：

  public static List GetFilteredCustomersDynamic(List customers, Func whereClause) { return customers .Where(whereClause).ToList(); } public static List GetFilteredCustomers(List customers, string letter) { return GetFilteredCustomersDynamic(c => c.LastName.Contains(letter)); } 

Answer 2

试试这个代码，

 public static List GetFilteredCustomersDynamic(List customers, Expression> whereClause) { return customers.Where(whereClause.Compile()).ToList(); } 

Answer 3

@elder_george，有一个拼写错误，表达式应该被编译以获得它的委托，否则这无法编译。

 return customers .Where(whereClause).ToList(); 

应该读作

 return customers .Where(whereClause.Compile()).ToList();