How to get IEnumerable<Foo> instead of IEnumerable<string> from LINQ?

Question

I am stuck on a LINQ query where I have being trying to return a list records from an SQL Table using EntityFramework 6, instead of getting that list, I keep end up getting an IEnumerable<string[]>.

This is what I have made to get IEnumerable<string[]>. I have an column in the table that needs to be split and then I test to see if a list contains those strings : The value in the table column columnOne can be something like this "a-b" or "b-c" etc, hence the need to use this s.columnOne.Split('-')

list<string> checkList = new list<string>();
checkList.add("a")
checkList.add("b")
checkList.add("c")

List<Foo> fooList = dbContext.Foos.ToList();

IEnumerable<string[]> items = fooList.Select(s => s.columnOne.Split('-'));

var result = items.SelectMany(x => x)
                  .Where(s => checkList.Contains(s)).ToList();

The above works as it should, but in the end it returns a list of string, which is not what I need.

I tried this below:

List<Foo> fooList = dbContext.Foos.ToList();

var test = fooList.Where(s => s.columnOne.Split('-'));

And this is where I run into the error and can go no further as I am ultimately trying to return a list of <Foo>, not <string>

Now I know that the Where clause needs to return a bool value such as fooList.Where(s => s.columnOne == "someString");, but I am at a loss as to how to go about structuring the LINQ query to get the results I am trying to get.

Any shove in the right direction would be great.

Answer 1

The where clause needs to contain the check against the checkList

var test = fooList.Where(foo => foo.columnOne.Split('-').Any(str => checkList.Contains(str)));

Answer 2

dbContext.Foos
    .ToList()
    .Where(foo => foo.columnOne.Split('-')
        .Any(x => checkList.Contains(x))

I hope you don't ever have very many Foos because that ToList function will read them all into memory. You'll need that, though, because I don't think Linq can understand how to translate that where statement. There are a few ways to get around that, if it's a problem to you.

Also, consider using a Set<string> instead of a List<string> for your checklist variable, as it'll perform better for membership checks like this one.