Как выбрать отличающиеся данные из БД с помощью Entity Framework?

Question

[Timbioz]

Есть таблица с повторяющимися данными по определенному ключу. Пример:

id Name CompanyId
1 Tim 1111111
2 Jack 126555
3 Tim 1111111
4 Kris 59911919
5 Tim 1111111
6 Jonh 1111111
7 Kim 1111111
8 Clark 9984848

Как выбрать значения, которые не имеют дубликатов по полю CompanyId
То есть: значения - 2, 4, 8

Answer 1

[Sergey Mozhaykin]

class Employee
{
	public int Id { get; set; }
	public string Name { get; set; }
	public int CompanyId { get; set; }
	
	public override string ToString()
	{
		return string.Format("Employee Id = {0}, Name = {1}, CompanyId = {2}", Id, Name, CompanyId);
	}
}

void Main()
{
	var employees = new Employee[] {
	    new Employee() {Id = 1, Name = "Tim", CompanyId = 1111111},
	    new Employee() {Id = 2, Name = "Jack", CompanyId = 126555},
	    new Employee() {Id = 3, Name = "Tim", CompanyId = 1111111},
	    new Employee() {Id = 4, Name = "Kris", CompanyId = 59911919},
	    new Employee() {Id = 5, Name = "Tim", CompanyId = 1111111},
	    new Employee() {Id = 6, Name = "John", CompanyId = 1111111},
	    new Employee() {Id = 7, Name = "Kim", CompanyId = 1111111},
	    new Employee() {Id = 8, Name = "Clark", CompanyId = 9984848},
	};
	
	var filtered = from emp in employees group emp by emp.CompanyId into g where g.Count() == 1 select g.FirstOrDefault();
	
	foreach (var emp in filtered)
	{
	    Console.WriteLine(emp);
	}
}

Answer 2

[Дмитрий Ковальский]

Коряво, но как-то так

var t = from c in Table
            where (from d in Table group d by d.CompanyId into dGroup
                   where dGroup.Count() ==1
                   select dGroup.CompanyId).Contains(c.CompanyId)
           select c