Question

我希望将3个表作为对象列表连接起来。这是我的三个表：

员工

部门

类别

Employee DepartmentID和CategoryID用于联接Department和Category Table。

这是我的Linq Join的外观

var result = from e in Employee.GetAllEmployees()
                         join d in Department.GetAllDepartments() on e.DepartmentID equals d.ID
                         join c in Cateory.GetAllCategories() on e.CategoryID equals c.ID
                         into eGroup
                         from c in eGroup.DefaultIfEmpty()
                         select new
                         {
                             Employee =e,
                             Department = d ==null? new Department() : d,
                             Cateory = c
                         };

我的问题是，我得到了两行不同的Employee ID = 1行，这是因为ID = 1的两个不同类别

我想将两个类别都放在同一个Employee节点中。员工ID = 1基本上是两个类别。

预期结果： CategoryA和CategoryB与员工标记相关。

我该如何实现？

感谢您的帮助！

这是重现我目前所拥有代码的代码。

class Program
{
    static void Main(string[] args)
    {
        var result = from e in Employee.GetAllEmployees()
                     join d in Department.GetAllDepartments() on e.DepartmentID equals d.ID
                     join c in Cateory.GetAllCategories() on e.CategoryID equals c.ID
                     into eGroup
                     from c in eGroup.DefaultIfEmpty()
                     select new
                     {
                         Employee =e,
                         Department = d ==null? new Department() : d,
                         Cateory = c
                     };

        Console.WriteLine("Hello World!");
        Console.ReadLine();
    }

    public class Employee
    {
        public int EmployeeID { get; set; }
        public string Name { get; set; }

        public int DepartmentID { get; set; }
        public int CategoryID { get; set; }

        public static List<Employee> GetAllEmployees()
        {
            return new List<Employee>()
                    {
                        new Employee { EmployeeID = 1, Name = "Mark", DepartmentID = 1, CategoryID = 1 },
                    };
        }
    }

    public class Department
    {
        public int ID { get; set; }
        public string DepartmentName { get; set; }

        public static List<Department> GetAllDepartments()
        {
            return new List<Department>()
                {
                    new Department { ID = 1, DepartmentName = "TECH"},
                    new Department { ID = 2, DepartmentName = "HR"},
                };
        }
    }

    public class Cateory
    {
        public int ID { get; set; }
        public string CategoryName { get; set; }

        public static List<Cateory> GetAllCategories()
        {
            return new List<Cateory>()
                {
                 new Cateory { ID = 1, CategoryName = "CategoryA"},
                 new Cateory { ID = 1, CategoryName = "CategoryB"},
                 new Cateory { ID = 2, CategoryName = "CategoryC"},
            };
        }
    }
}

Answer 1

我真的没有办法进行测试，但是您应该可以通过更新查询来进行左联接

 var result = from e in Employee.GetAllEmployees()
                 join d in Department.GetAllDepartments() on e.DepartmentID equals d.ID into d_def
                 from d in d_def.DefaultIfEmpty()
                 join c in Cateory.GetAllCategories() on e.CategoryID equals c.ID into c_def
                 from c in c_def.DefaultIfEmpty())
                 select new
                 {
                     Employee =e,
                     Department = d ==null? new Department() : d,
                     Cateory = c
                 };

Answer 2

这是您的结果。这两个雇主具有相同的ID号

C＃LINQ左联接3个表/列表

2 个答案: