SQL to LINQ conversion for asp.net IQueryable

Question

How to translate the flowing sql query into linq so I can use inside my web api controller.

select * from String where StringNumber in 
(
select Str1 from Detail where DetailNr = 6
union 
select Str2 from Detail where DetailNr = 6
union 
select Str3 from Detail where DetailNr = 6
union 
select Str4 from Detail where DetailNr = 6
)

I have tried to select the individual string numbers and I came up with this:

var str1 = _dataContext.Context.Detail.AsQueryable()
    .Where(n => n.DetailNr == 6)
    .Select(n => n.Str1 );
var str2 = _dataContext.Context.Detail.AsQueryable()
    .Where(n => n.DetailNr == 6)
    .Select(n => n.Str2 );
var str3 = _dataContext.Context.Detail.AsQueryable()
    .Where(n => n.DetailNr == 6)
    .Select(n => n.Str3 );
var str4 = _dataContext.Context.Detail.AsQueryable()
    .Where(n => n.DetailNr == 6)
    .Select(n => n.Str4 );

then something like this:

var result= _dataContext.Context.String.AsQueryable()
    .Where(s => s.StringNumber == str1 or str2 or str2 or str4).ToList();

How should this be written in an asp.net MVC controller? Maybe use a SelectMany clause?

Answer 1

This will work for Linq to Objects, but may not be supported by Linq to Entities:

var strings = _dataContext.Context.Detail.AsQueryable()
    .Where(n => n.DetailNr == 6)
    .Select(n => new [] {n.Str1, n.Str2, n.Str3, n.Str4});
    .SelectMany(s => s);

var result= _dataContext.Context.String.AsQueryable()
    .Where(s => strings.Contains(s)).ToList();

You may need to add as AsEnumerable to hyrdate the list.

Answer 2

var results =  _dataContext.Context.Detail.Where (n => n.DetailNr == 6).ToList();

var concattedResults = results.Select(n => n.Str1)
.Concat(results.Select(n => n.Str2))
.Concat(results.Select(n => n.Str3))
.Concat(results.Select(n => n.Str4)).ToList();