Linq 和 Lambda 查询中按照多个值进行分组GroupBy

创建要查询的对象： class Employee { public int ID { get;set; } public string FName { get; set; } public int Age { get; set; } public char Sex { get; set; } }

如果对这个类的Age和Sex的连个字段进行分组，方法如下：

// 先造一些数据 List<Employee> empList = new List<Employee>(); empList.Add(new Employee() { ID = 1, FName = "John", Age = 23, Sex = 'M' }); empList.Add(new Employee() { ID = 2, FName = "Mary", Age = 25, Sex = 'F' }); empList.Add(new Employee() { ID = 3, FName = "Amber", Age = 23, Sex = 'M' }); empList.Add(new Employee() { ID = 4, FName = "Kathy", Age = 25, Sex = 'M' }); empList.Add(new Employee() { ID = 5, FName = "Lena", Age = 27, Sex = 'F' }); empList.Add(new Employee() { ID = 6, FName = "Bill", Age = 28, Sex = 'M' }); empList.Add(new Employee() { ID = 7, FName = "Celina", Age = 27, Sex = 'F' }); empList.Add(new Employee() { ID = 8, FName = "John", Age = 28, Sex = 'M' });

接下来的做法是：

// 实现多key分组的Linq扩展函数版本 var sums = empList .GroupBy(x => new { x.Age, x.Sex }) .Select(group => new { Peo = group.Key, Count = group.Count() }); foreach (var employee in sums) { Console.WriteLine(employee.Count + ": " + employee.Peo); } // 实现多key分组的lambda版本 var sums2 = from emp in empList group emp by new { emp.Age, emp.Sex } into g select new { Peo = g.Key, Count = g.Count() }; foreach (var employee in sums) { Console.WriteLine(employee.Count + ": " + employee.Peo); } 其他示例： 【Lambda示例】 List<AddressBookPersonDto> bookPersons = (from a in addressClassPersons where a.AddressBookPerson != null select a.AddressBookPerson).ToList().MapTo<List<AddressBookPersonDto>>().GroupBy(a => new { a.Id, a.Name, a.JobTitle, a.FixedTelephone, a.MobilePhone, a.Email, a.OrganizationId }) .Select(g => new AddressBookPersonDto() { Id = g.Key.Id, Name = g.Key.Name, JobTitle = g.Key.JobTitle, FixedTelephone = g.Key.FixedTelephone, MobilePhone = g.Key.MobilePhone, Email = g.Key.Email, OrganizationId = g.Key.OrganizationId, OrganizationName = g.Key?.OrganizationId > 0 ? _organizationManager.GetOrganization(g.Key.OrganizationId).DisplayName : String.Empty }).ToList(); 【Linq示例】 List<AddressBookPersonDto> addressBookPersons = (from a in addressClassPersons where a.AddressBookPerson != null group a by new { a.AddressBookPerson.Id, a.AddressBookPerson.Name, a.AddressBookPerson.JobTitle, a.AddressBookPerson.FixedTelephone, a.AddressBookPerson.MobilePhone, a.AddressBookPerson.Email, a.AddressBookPerson.OrganizationId } into g select new AddressBookPersonDto() { Id = g.Key.Id, Name = g.Key.Name, JobTitle = g.Key.JobTitle, FixedTelephone = g.Key.FixedTelephone, MobilePhone = g.Key.MobilePhone, Email = g.Key.Email, OrganizationId = g.Key.OrganizationId, OrganizationName = g.Key?.OrganizationId > 0 ? _organizationManager.GetOrganization(g.Key.OrganizationId).DisplayName : String.Empty }).ToList();