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How to return IQueryable LINQ result from two joined tables into a List<string>?

This is an add-on question to one asked here: Entity Framework Core 5.0 How to convert LINQ for many-to-many join to use Intersection table for ASP.NET Membership
How can I return the results of an the following LINQ IQueryable result, which is from two join tables, for the RoleName column to a List<string>?
var queryResult = (this.DbContext.aspnet_UsersInRoles
.Where(x => x.UserId == dpass.UserId)
.Join(
this.DbContext.aspnet_Roles,
ur => ur.RoleId,
r => r.RoleId,
(ur, role) => new
{
ur,
role
}
)
.Select(x => new { x.ur.UserId, x.role.RoleName })
);
UPDATE 1
I need the List in the form of an array of values so that I can use the Contains() method. I need to search for specific RoleNames assigned to a UserId. If I use ToList() on the IQueryable, then the array result is in the form of:
{ RoleName = "admin"}
{ Rolename = "user"}
I am unable to use the .Contains() method because I get the following error:
cannot convert from 'string' to <anonymous type: string RoleName>.
It seems be to expecting a class that the query result can be assigned to. But, one doesn't exist because I am doing this on-the-fly.
UPDATE 2
I need the queryResult in a List that is in the form of:
{ "admin"}
{ "user"}
With this output, I can use the .Contains() method to perform multiple checks. This is used for determining Windows Forms field properties. So, if the UserId belongs to the admin role then the form enables certain check boxes and radio buttons whereas if the UserId belongs to the user role then the form enables different check boxes. This is not an exhaustive list of roles available along with the checks that are performed by the form. But, what is important is that there are multiple checks on the List that need to be performed in separate IF statements.
Currently, I am able to use the queryResult to do the following:
Get a list of the RoleNames
Perform separate LINQ queries on the queryResult by checking for the specific RoleName
Perform a .Count() > 0 check to see if the UserId is in a specific role.
This seems like an ugly hack because I have the intermediate step of creating 1 + N variables to retrieve, by LINQ, and store each RoleName and then check to see if the .Count() is greater than zero. I think that the List method would be cleaner and more efficient. If that is possible.
var varUser = from d in queryResult
where d.RoleName == "user"
select new { d.RoleName };
var varAdmin = from u in queryResult
where u.RoleName == "admin"
select new { u.RoleName };
//... more declarations and LINQs ...

Short answer:
Select only the RoleName, and use SelectMany instead of Select
Better answer
So you have a table of Roles, and a table of Users (I'm simplifying your long identifiers, not part of the problem and way too much typing).
There seems to be a many to many relation between Roles and Users: Every Role is a role for zero or more Users, every User has zero or more Roles.
This many-to-many relation is implemented using a standard junction table: UsersInRoles. This junction table has two foreign keys: one to the User and one to the Roles.
You have a UserId, and it seems that you want all names of all Roles of the user that has this Id.
How about this:
int userId = ...
// Get the names of all Roles of the User with this Id
var namesOfRolesOfThisUser = dbContext.UsersInRoles
// only the user with this Id:
.Where(userInRole => userInRole.UserId == userId)
// get the names of all Roles for this userInRole
.SelectMany(userInRole => dbContext.Roles.Where(role => role.RoleId == userInRole.RoleId)
.Select(role => role.RoleName));
In words: from the table of UsersInRoles, keep only those UsersInRoles that have a value for property UserId that equals userId.
From every one of the remaining UsersInRoles, select all Roles that have a RoleId that equeals the UserInRole.RoleId. From these Roles take the RoleName.
I use SelectMany to make sure that I get one sequence of strings, instead of a sequence of sequences of strings.
If you suspect double RoleNames, consider to append Distinct() at the end.
But I want to Join!
Some people really like to do the joins themselves.
int userId = ...
var namesOfRolesOfThisUser = dbContext.UsersInRoles
.Where(userInRole => userInRole.UserId == userId)
.Join(dbContext.Roles,
userInRole => userInRole.RoleId, // from every UserInRole take the foreign key
role => role.RoleId, // from every Role take the primary key
// when they match, take only the name of the Role
(userInRole, role) => role.RoleName);

Try to use GroupBy(). Be careful, this method is not supported by direct IQueryable to SQL conversion. If you will try to call GroupBy() before .ToList(), it will throw an error.
In your example you could this: select a list in memory and then work with it:
var queryResult = (this.DbContext.aspnet_UsersInRoles
.Where(x => x.UserId == dpass.UserId)
.Join(this.DbContext.aspnet_Roles,
ur => ur.RoleId,
r => r.RoleId,
(ur, role) => new { ur, role }
)
.Select(x => new { x.ur.UserId, x.role.RoleName })
.ToList() // MATERIALIZE FIRST
.GroupBy(x => x.UserId) //ADD THIS
);
queryResult.Contains(roleName=> roleName == "ROLE_TO_SEARCH")
var userId = queryResult.Key;

How to query Entity Framework objects where select is a list

I am trying to do something simple, but I can't figure it out. Using EF6, I have 2 tables which are associated by an intermediate associative table, giving a many-to-many relationship:
I want to query all users who belong to a list of families. So I get an array of families:
var db = new MyProjectEntities();
User user = GetUserById((int)HttpContext.Current.Session["CurrentUserId"]);
var families = db.Users.Where(u => u.UserId == user.UserId).First().Families.ToArray();
Then I want to query all users belonging to these families:
var users = db.Users.Where(u => families.Contains(u.Families));
But I get this error:
Instance argument: cannot convert from 'Database.Family[]' to 'System.Linq.IQueryable>'
Thanks in advance.

You can use Any method:
var users = db.Users.Where(u => u.Families.Any(fam => families.Contains(fam))).AsEnumerable();
I think this is what you're searching for.

EF/Linq - Sort collection before grouping

I have a one-to-many relationship between a project table and an audit table. I'm trying to pick out from the audit table the latest entry for each project entity.
From what I understand to do this I should be able to sort my audit collection by date before grouping by project id, so that I can select the first entry for each group (project id) to get the latest entry.
But when I run my ef/linq query, the results are not correct and the order-by seems to be ignored - even the generated sql doesn't include the order by statement.
Heres the simple example I've tried.
using (var ctx = new MyDbContext())
{
var audit = from a in ctx.ProjectAudits
orderby a.CreatedDate descending
group a by a.ProjectId into grp
select grp.FirstOrDefault();
var resultsList = audit.ToList();
}
The results always return with the earliest audit entry for each project id and not the latest.
Is there something wrong with this query; am I missing something obvious?

UPDATE
Okay, how about this?
ctx.ProjectAudits
.GroupBy(p => p.ProjectId)
.Select(p => p.OrderByDescending(j => j.CreatedDate).FirstOrDefault())
.ToList();
Don't have VS with me here, but it should theoretically group your records, order them within the group by their creation date, and select the first record from each group.

I think you need to look at a different approach. Instead of ordering, why don't you group and then select the audit with the maximum CreatedDate. I've not tested the following and am just throwing it out there:
var audit = from a in ctx.ProjectAudits
group a by a.ProjectId into grp
select new {
// whatever your other properties are
CreatedDate = grp.Max(i => i.CreatedDate)
};
Or, as most people prefer the method syntax:
var audit = ctx.ProjectAudits
.Where(i => i.CreatedDate == ctx.ProjectAudits
.Max(x => x.CreatedDate));
EDIT - made some changes, and tested with a test class and a List<TestClass> and the above works with that.

How can i do it using linq2sql...?

I have a table Users. Users has a column rating. How i can get information about user place using linq2sql? I want method like:
var userPlace =
GetUserPlaceById(userId);
Table Users may contains a few thousands users.
Sorry guys. Users DOESNT contain place column. Real example: Rating is chess elo rating. if you have high rating then you on 1st place. If you have lower rating then you on the last place.

Did you mean something like this?
int userRating = users.Single(user => user.Id = userId).Rating;
int userPlace = users.Where(user => user.Rating < userRating).Count() + 1;

I have a table Users. Users has a column rating. How i can get information about user place using linq2sql?
I'm not sure what "userPlace" is, but assuming it is a column in that table...
var userPlace = (from user in db.Users
where user.Id == userId
select user)
.First()
.UserPlace;
Be aware that calling .First() will throw an exception if no match is found, so if you expect that sometimes this user will not exist use FirstOrDefault, check for null, and then grab the UserPlace property.

You would use something like:
string GetUserPlaceById(int userId)
{
IQueryable<User> users = GetUsers(); // Get users queryable reference
return users.Single(user => user.Id == userId).Place;
}

You could do something like this:
var userPlace = _db.Users.Where(x => x.UserId == userId).Select(x => x.Place).SingleOrDefault();

is there a better way to write this frankenstein LINQ query that searches for values in a child table and orders them by relevance?

I have a table of Users and a one to many UserSkills table. I need to be able to search for users based on skills. This query takes a list of desired skills and searches for users who have those skills. I want to sort the users based on the number of desired skills they posses. So if a users only has 1 of 3 desired skills he will be further down the list than the user who has 3 of 3 desired skills.
I start with my comma separated list of skill IDs that are being searched for:
List<short> searchedSkillsRaw = skills.Value.Split(',').Select(i => short.Parse(i)).ToList();
I then filter out only the types of users that are searchable:
List<User> users = (from u in db.Users
where
u.Verified == true &&
u.Level > 0 &&
u.Type == 1 &&
(u.UserDetail.City == city.SelectedValue || u.UserDetail.City == null)
select u).ToList();
and then comes the crazy part:
var fUsers = from u in users
select new
{
u.Id,
u.FirstName,
u.LastName,
u.UserName,
UserPhone = u.UserDetail.Phone,
UserSkills = (from uskills in u.UserSkills
join skillsJoin in configSkills on uskills.SkillId equals skillsJoin.ValueIdInt into tempSkills
from skillsJoin in tempSkills.DefaultIfEmpty()
where uskills.UserId == u.Id
select new
{
SkillId = uskills.SkillId,
SkillName = skillsJoin.Name,
SkillNameFound = searchedSkillsRaw.Contains(uskills.SkillId)
}),
UserSkillsFound = (from uskills in u.UserSkills
where uskills.UserId == u.Id && searchedSkillsRaw.Contains(uskills.SkillId)
select uskills.UserId).Count()
} into userResults
where userResults.UserSkillsFound > 0
orderby userResults.UserSkillsFound descending
select userResults;
and this works! But it seems super bloated and inefficient to me. Especially the secondary part that counts the number of skills found.
Thanks for any advice you can give.
--r

I think that should do the trick:
(from u in users
where u.UserSkills.Any(skill => searchedSkillsRaw.Contains(skill.SkillId))
select new
{
u.Id,
u.FirstName,
u.LastName,
u.UserName,
UserPhone = u.UserDetail.Phone,
UserSkills = u.UserSkills,
UserSkillsFound = u.UserSkills.Where(skill => searchedSkillsRaw.Contains(skill.SkillId)).Count()
} into userResults
orderby userResults.UserSkillsFound descending
select userResult).ToList();
However, since this is a query that gets executed on SQL server I strongly recommend to remove the 'ToList()' call from the first query. Because that actually causes LINQ to run two separate queries on the SQL server. You should change it to IQueryable instead. The power of LINQ is to construct queries in several steps without having to actually execute it in between. So 'ToList' should be called only at the end when the entire query has been constructed. In fact what you currently do is running the second query in memory rather than on the database server.
In regards to your UserSkills one-to-many relation you do not need to do an explicity join in LINQ. You can just access the collection property instead.
Let me know if you need more explanation.
Michael

Why not just let people do, say, fUsers.UserSkills.Count()? It would reduce the amount of data retrieved from the server in the first place.
Alternatively, you could create a View that has a calculated field in it and then map that to a type. Would push the query for count down into the DB.