C# Linq Intersect

Question

Most of the time I just use foreach statements, because that is a lot easier for me to code. Later on, when my code is done, I convert the foreach into LINQ statements where it makes sense.

I want to learn how to write good readable LINQ statements. How would you guys convert this foreach code into a correct LINQ statement ?

private List<QARoles> GetUserRoles(User user)
{
    //TODO: Fix this with LINQ intersect.

    var result = new List<QARoles>();
    foreach (var role in user.Roles)
    {
        foreach (QARoles qarole in System.Enum.GetValues(typeof(QARoles)))
        {
            if (role.Name.Equals(qarole.ToString()))
            {                        
                result.Add(qarole);
            }                    
        }
    }
    return result;
}

I have used resharper, just like Malte R mentioned. But I do not like the outcome. I don't think it is nice to read. — Tony_KiloPapaMikeGolf, Oct 11 '16 at 14:14
As you can see looking at all these answers : the best answer was not generated by resharper. It takes great skills to write decent LINQ statements that are readable. — Tony_KiloPapaMikeGolf, Oct 11 '16 at 14:48
I completely agree :) and as a question this is a worthy one - my only point is that please when posing show what you have tried. We can help you from there :) — Gilad Green, Oct 11 '16 at 14:49

score 1 · Answer 1 · answered Oct 11 '16 at 14:08

1

You can do this:

var roles=System.Enum.GetValues(typeof(QARoles));
return roles.Where(r=>user.Roles.Any(role=>role.Name.Equals(r.ToString())).ToList();

answered Oct 11 '16 at 14:08

ocuenca

38,548
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decPL · Accepted Answer · 2016-10-11T14:52:52.713

1

This can be simplified to:

var result = user.Roles
                 .Where(r => Enum.IsDefined(typeof(QARoles), r.Name))
                 .Select(r => (QARoles)Enum.Parse(typeof(QARoles), r.Name))
                 .ToList();

edited Oct 11 '16 at 14:52

answered Oct 11 '16 at 14:08

decPL

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You return a list of User.Roles. It should be List ;-) – Tony_KiloPapaMikeGolf Oct 11 '16 at 14:35
@Tony_KiloPapaMikeGolf yes, too much code today - fixed now. Still pretty readable hopefully. – decPL Oct 11 '16 at 14:37
You deserve the credits for best answer ! Alas, my reputation is less than 15. And someone gave -1 for my question, so I am even lower now. – Tony_KiloPapaMikeGolf Oct 11 '16 at 14:42
You should still be able to accept that answer. Just saying... :P – decPL Oct 11 '16 at 14:44

score 0 · Answer 3 · answered Oct 11 '16 at 14:08

return (from role in user.Roles 
        from QARoles qarole in System.Enum.GetValues(typeof(QARoles))
        where role.Name.Equals(qarole.ToString()) 
        select qarole)
.ToList();

or

 return user.Roles.SelectMany(role => System.Enum.GetValues(typeof(QARoles)).Cast<QARoles>(),
            (role, qarole) => new {role, qarole})
         .Where(t => t.role.Name.Equals(t.qarole.ToString())).Select(t => t.qarole).ToList();

score 0 · Answer 4 · answered Oct 11 '16 at 14:09

using ReSharper:

            return (from role in user.Roles
                from QARoles qarole 
                in System.Enum.GetValues(typeof(QARoles))
                where role.Name.Equals(qarole.ToString())
                select qarole)
                .ToList();

score 0 · Answer 5 · answered Oct 11 '16 at 14:10

0

return System.Enum.GetValues(typeof(QARoles)).Where(role => 
user.Roles.Any(r => r.Name == role.ToString()))

answered Oct 11 '16 at 14:10

Ashley John

2,379
2
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score 0 · Answer 6 · answered Oct 11 '16 at 14:25

0

I came up with this myself:

    return user.Roles
        .Select(r => r.Name).ToList<string>()
        .Select(str =>
        {
            QARoles qarole;
            bool success = System.Enum.TryParse(str, out qarole);
            return new { qarole, success };
        })
        .Where(pair => pair.success)
        .Select(pair => pair.qarole)
        .ToList();

But I dont think it has become better readable ;-)

answered Oct 11 '16 at 14:25

Tony_KiloPapaMikeGolf

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12
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Started writing a comment on how you could slightly improve on that - but realized it can be written in a much simpler way - check my answer. – decPL Oct 11 '16 at 14:31

C# Linq Intersect

6 Answers6