列出特定角色的所有用户

Question

In ASP.NET Core 2.2 MVC I'm trying to get a list of all users in a specific role.
Fx. list of all users in role named "Admin":

var idsWithPermission = _userManager.GetUsersInRoleAsync("Admin").Result;
var users = _db.ApplicationUser.Where(u => idsWithPermission.Contains(u.Id)).ToListAsync();
return(users);

Compiler fails "u.Id" here: idsWithPermission.Contains(u.Id)

Error: Argument 1: Cannot convert from "string" to Microsoft.AspNetCore.Identity.IdentityUser

This is a newbie questions, so might be very simple for a shark:-) Thanks a lot in advance...

Answer 1

GetUsersInRoleAsync returns a list of IdentityUser objects. To get a list of IDs, you need to access the Id property of these objects.

// Get a list of users in the role
var usersWithPermission = _userManager.GetUsersInRoleAsync("Admin").Result;

// Then get a list of the ids of these users
var idsWithPermission = usersWithPermission.Select(u => u.Id);

// Now get the users in our database with the same ids
var users = _db.ApplicationUser.Where(u => idsWithPermission.Contains(u.Id)).ToListAsync();

return users;

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Note that using .Result on an async method is not advised, because it can lead to deadlocks. Instead use await and make your method async .

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Also note that depending on your setup, if ApplicationUser inherits from IdentityUser and the identity system is correctly configured, GetUsersInRoleAsync will already return ApplicationUser objects and you only need to cast them to the correct type:

// Get a list of users in the role
var usersWithPermission = _userManager.GetUsersInRoleAsync("Admin").Result;
var users = usersWithPermission.OfType<ApplicationUser>();

return users;