通过实体框架中的元素ID获取元素列表 [英] Get a list of elements by their ID in entity framework

问题描述

如何通过ID获取另一个列表中的所有元素?例如我具有列表角色；我想通过ID从此列表中的数据库中获取所有角色.

How can I get all elements that are in another list by ID? For eg; I have List roles; I'd like to get all roles from the database that are in this this list by their Id.

我使用代码优先.

我这样做了，它引发了一个错误:

I did this and it threw an error:

var roles = db.Roles.Where(r => user.Roles.Any(ur => ur.RoleId == r.RoleId));

RoleId的类型为int.

错误:

无法创建类型为'SampleMVC.Domain.Role'的常量值.在这种情况下，仅支持基本类型(例如Int32，String和Guid).

Unable to create a constant value of type 'SampleMVC.Domain.Role'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

推荐答案

var listOfRoleId = user.Roles.Select(r => r.RoleId);
var roles = db.Roles.Where(r => listOfRoleId.Contains(r.RoleId));

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