如何在C#中使用LINQ和Lambda來進行Join操作？

內連接只傳回那些在兩個表中符合或存在的記錄或行。我們也可以根據條件在多個表上套用連接，如下所示。

如果我們需要根據多個條件進行連接，請使用匿名類型。

在下面的範例中，我們寫了兩種可以用於在Linq中進行連接的方法 這裡部門和員工被連接起來

範例

class Program{
   static void Main(string[] args){
      var result =
      Employee.GetAllEmployees().Join(Department.GetAllDepartments(),
      e => e.DepartmentID,
      d => d.ID, (employee, department) => new{
         EmployeeName = employee.Name,
         DepartmentName = department.Name
      });
      foreach (var employee in result){
         Console.WriteLine(employee.EmployeeName + "\t" +
         employee.DepartmentName);
      }
      var result1 = from e in Employee.GetAllEmployees()
      join d in Department.GetAllDepartments()
      on e.DepartmentID equals d.ID
      select new{
         EmployeeName = e.Name,
         DepartmentName = d.Name
      };
      foreach (var employee in result1){
         Console.WriteLine(employee.EmployeeName + "\t" +
         employee.DepartmentName);
      }
      Console.ReadLine();
   }
}
public class Employee{
   public int ID { get; set; }
   public string Name { get; set; }
   public int DepartmentID { get; set; }
   public static List<Employee> GetAllEmployees(){
      return new List<Employee>(){
         new Employee { ID = 1, Name = "A", DepartmentID = 1 },
         new Employee { ID = 2, Name = "B", DepartmentID = 2 },
         new Employee { ID = 3, Name = "B", DepartmentID = 1 },
         new Employee { ID = 4, Name = "V", DepartmentID = 1 },
         new Employee { ID = 5, Name = "F", DepartmentID = 2 },
         new Employee { ID = 6, Name = "R", DepartmentID = 2 },
         new Employee { ID = 7, Name = "TT", DepartmentID = 1 },
         new Employee { ID = 8, Name = "YY", DepartmentID = 1 },
         new Employee { ID = 9, Name = "WW", DepartmentID = 2 },
         new Employee { ID = 10, Name = "QQ"}
      };
   }
}
public class Department{
   public int ID { get; set; }
   public string Name { get; set; }
   public static List<Department> GetAllDepartments(){
      return new List<Department>(){
         new Department { ID = 1, Name = "IT"},
         new Department { ID = 2, Name = "HR"},
         new Department { ID = 3, Name = "Contract"},
      };
   }
}

輸出

A IT
B HR
B IT
V IT
F HR
R HR
TT IT
YY IT
WW HR
A IT
B HR
B IT
V IT
F HR
R HR
TT IT
YY IT
WW HR

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