Question

我有两个数据来源说：

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

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

并填充了一些数据：

 var data1 = new List<Person>() { new Person() { Id = 1, Name = "data 11" }, new Person() { Id = 2, Name = "data 12" } };

 var data2 = new List<Employee>() { new Employee() { Id = 1, Name = "data 21" }, new Employee() { Id = 2, Name = "data 22" }, new Employee() { Id = 3, Name = "data 23" } };

我已创建查询以将Left Join设为：

    var query = (from person in (data1)
                        join employee in (data2) on person.Id equals employee.Id
                            into temp
                        from y in temp.DefaultIfEmpty()
                        select new { Data = y }).ToList();

现在我的问题是： - 我想从源代码制作父母或者＃34;＆＃34;一个数据源具有更高的Count。

场景就像：if data1.Count＆gt; data2.Count那么：与上述查询相同

如果data2.Count＆gt; data1.Count那么：

                      var query =  (from employee in (data2)
                        join person in (data1) on employee.Id equals                       
                         person.Id
                            into temp
                        from y in temp.DefaultIfEmpty()
                        select new { Data = y }).ToList();

我怎样才能实现这一目标，因为Linq不提供开箱即用的权利加入Linq？请指导。

Answer 1

如果您可以定义两个实体都实现的接口，那么您可以基于此接口一般性地编写查询：

  interface INameIdPair {
    int Id { get; set; }
    string Name { get; set; }
  }

  public class Person : INameIdPair {
    public int Id { get; set; }
    public string Name { get; set; }
  }

  public class Employee : INameIdPair {
    public int Id { get; set; }
    public string Name { get; set; }
  }

  var data1 = new List<INameIdPair> {
    new Person { Id = 1, Name = "data 11" },
    new Person { Id = 2, Name = "data 12" }
  };

  var data2 = new List<INameIdPair> {
    new Employee { Id = 1, Name = "data 21" },
    new Employee { Id = 2, Name = "data 22" },
    new Employee { Id = 3, Name = "data 23" }
  };

  var from1 = data1.Count > data2.Count ? data1 : data2;
  var from2 = from1 == data1 ? data2 : data1;

  var query =
    (from ff1 in from1
      join ff2 in from2 on ff1.Id equals ff2.Id
        into temp
      from y in temp.DefaultIfEmpty()
      select new {Data = y}
      ).ToList();

Linq Left Join在桌面上有更多的记录

1 个答案: