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问题描述

模糊方案:一个人有零个,一个或多个宠物。



使用Linq到Sql, code> IQueryable 给定personID的宠物列表。
这里是ERD的糟糕的/被屠杀/混淆的部分:





代码

  public IQueryable< Pet> GetPersonPets(int personID)
{
var personPets = from p in Person
其中p.ID == somePersonID
select p.Pets;

return personPets; // fail
// return(IQueryable< Pet>)personPets //也失败
// return personPets.AsQueryable< Pet>()//也失败
}



引发异常

 
不能隐式转换类型
'System.Collections.Generic.IEnumerable(System.Data.Linq.EntitySet(Pet))''
到'System.Linq.IQueryable(Pet)' 。
存在显式转换(是否缺少转换?)

尝试失败

直接转换无效:(IQueryable< MyType>)


$ b b

调用集合方法 AsQueryable 无效: .AsQueryable< MyType>()



问题



如何将LinqToSql查询的结果正确转换为 IQueryable

解决方案

关系):

  IQueryable< Pet> personPets =(
from p in db.Person
其中p.ID == somePersonID
select p
).Single()。Pets.AsQueryable();

虽然我可能会用这种方式写一些变化:

  var personPets = 
db.Person.Single(t => t.Id == somePersonId).Pets.AsQueryable


Obfuscated Scenario: A person has zero, one or many pets.

Using Linq to Sql, the need is to get an IQueryable list of pets for the given personID.Here's the poorly mangled/butchered/obfuscated portion of the ERD:

Code:

 public IQueryable<Pet> GetPersonPets(int personID)
    {
        var personPets= from p in Person
        where p.ID == somePersonID
        select p.Pets;

        return personPets; //fail
        // return (IQueryable<Pet>)personPets  //also fail
        // return personPets.AsQueryable<Pet>()  //also fail
    }

Exception Raised:

Cannot implicitly convert type
'System.Collections.Generic.IEnumerable (System.Data.Linq.EntitySet(Pet))'
to 'System.Linq.IQueryable(Pet)'.
An explicit conversion exists (are you missing a cast?)

Failed Attempts:

Direct casting didn't work: (IQueryable<MyType>)

Calling collection method AsQueryable didn't work: .AsQueryable<MyType>()

Question:

How can you cast the results of the LinqToSql query properly to IQueryable?

解决方案

This works for me (with different tables of course, but same relationship):

IQueryable<Pet> personPets = (
   from p in db.Person
   where p.ID == somePersonID
   select p
).Single().Pets.AsQueryable();

Although I'd probably write it in some variation of this way:

var personPets =
    db.Person.Single(t => t.Id == somePersonId).Pets.AsQueryable();

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08-18 13:11