Question

我有两个表动物和马戏团，它们具有多对多关系，从而产生了关联类 Contract ，我有一个品种类，该类通过一对多关系与动物相关联。如何找到具有最多马戏团动物数量的品种。

我已经尝试过了：

var req = from Animal A in Contract
                     group A by A.Breed into g
                     select max { g.Key, Count = g.Count() };

但是它不起作用我的意思是，例如，我们有：

**Animal_FK**      **Circus_FK**     **Salary**    **Contract_ date**      
----------          ----------      ------------    -------------------

   S3                  C10             3000           2015-12-12

   S1                  C12             5000           2010-10-17

   D2                  C18             4000           2016-02-22

   B4                  C85             3500           2018-09-30

   S2                   C6              2700           2014-05-10


Animal_key        Name          
-------------  -------------          
    S1            Python 
    S2            Cobra              
    S3            Boa              
    D1            Bulldog              
    D2            Labrador              
    B1            Owl
    B2            Dove   





Beer_Key      Name         Description    
----------  ---------    ----------------                    
   S          Snake            reptile      
   D          Dog              pet     
   B          Birds            flying animals

查询结果将为蛇

Answer 1

我假设这里有一些POCO。我不会提供诸如薪水等其他详细信息，而只是最低限度。

public class Breed
{
    public string Name { get; set; }
}

public class Animal
{
    public string Name { get; set; }
    public Breed Breed { get; set; }
}

public class Circus
{
    public string Name { get; set; }
}

public class Contract
{
    public Animal Performer { get; set; }
    public Circus Venue { get; set; }
}

然后设置一些数据，以表示您上面的信息。

var breeds = new[]
{
    new Breed {Name = "Snake"},
    new Breed {Name = "Dog"},
    new Breed {Name = "Bird"}
};

var animals = new[]
{
    new Animal{Name="Boa", Breed = breeds[0]},     // 0
    new Animal{Name="Python", Breed = breeds[0]},  // 1
    new Animal{Name="Cobra", Breed = breeds[0]},   // 2
    new Animal{Name="Bulldog", Breed = breeds[1]}, // 3
    new Animal{Name="Labrador", Breed = breeds[1]},// 4
    new Animal{Name="Dove", Breed = breeds[1]},    // 5
    new Animal{Name="Owl", Breed = breeds[2]},     // 6
};

var circuses = new[]
{
    new Circus {Name = "C1"},
    new Circus {Name = "C2"},
    new Circus {Name = "C3"},
    new Circus {Name = "C4"},
    new Circus {Name = "C5"},
};

var contracts = new[]
{
    new Contract {Performer = animals[0], Venue = circuses[0]},
    new Contract {Performer = animals[1], Venue = circuses[1]},
    new Contract {Performer = animals[2], Venue = circuses[2]},
    new Contract {Performer = animals[4], Venue = circuses[3]},
    new Contract {Performer = animals[6], Venue = circuses[4]},
};

然后这就是您获得最具代表性的品种的方法：

var mostRepresentedBreed = (
        from contract in contracts
        group contract by contract.Animal.Breed
        into contractsByBreed
        orderby contractsByBreed.Count() descending
        select contractsByBreed.Key
    ).FirstOrDefault();

var theWinnerIs = mostRepresentedBreed.Name;

希望这会有所帮助。布雷特。

通过关联类检索数据

1 个答案: