SelectMany已应用于3个列表

问题描述

我需要创建使用3个实体框架实体(用户，EnrolmentType和OrganizationEnrolment)创建的对象列表OrganizationEnrolment:

I need to create a list of objects, OrganizationEnrolment, created using 3 Entity Framework entities (User, EnrolmentType and OrganizationEnrolment):

List<OrganizationEnrolment> organizationEnrolments = 
  context.Organizations
  .SelectMany(x => context.Users)
  .SelectMany(x => context.EnrolmentTypes)
  .Select(y => new OrganizationEnrolment {
     EnrolmentType = enrolmentType
     Organization = organization,
     User = user
   })

我的问题是在拥有SelectMany之后如何从3个联接表中获取enrolmentType，组织和用户?请注意以下代码:

My problem is after having the SelectMany how to get the enrolmentType, organization and user from the 3 joined table? Note that the following code:

EnrolmentType = enrolmentType,
Organization = organization,
User = user

不起作用，因为我没有变量enrolmentType，组织和用户.

is not working because I do not have the variables enrolmentType, organization and user.

推荐答案

您可以使用查询语法来获取所有这些变量:

You can use query syntax to get all those variables:

from o in context.Organizations
from u in context.Users
from et in context.EnrolmentTypes
select new OrganizationEnrolment {
     EnrolmentType = et
     Organization = o,
     User = u
   }

每个本地范围变量将在select语句中可见.

Each local range variable will be visible in select statement.

Lambda语法(已通过EF6检查):

Lambda syntax (checked with EF6):

context.Organizations.SelectMany(
          o => context.Users.SelectMany(
              u => context.EnrolmentTypes.Select(
                  et => new OrganizationEnrolment {
                       EnrolmentType = et
                       Organization = o,
                       User = u
                  })
              )
         )

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