Filter (Triple) Nested Collection using Linq C#

Question

I need to filter a List of collections > Repos > Workflows and return the result in the same format

Hopefully the example is fairly clear please shout if you think it needs more detail.

    // All classes have a property 'Name'
    // Filter along the branch for any that match and return only the matching items

    List<Collection> AllCollections = new List<Collection>();
    Collection CollectionA = new Collection();
    Collection CollectionB = new Collection();
    CollectionA.Repos = new List<Repo>{new Repo{Name = "FirstRepo", Workflows = new List<Workflow>{new Workflow{Name = "CI-CD"}, new Workflow{Name = "Tests"}, new Workflow{Name = "First-Ops"}}}, new Repo{Name = "SecondRepo", Workflows = new List<Workflow>{new Workflow{Name = "CI-CD"}, new Workflow{Name = "Testing"}, new Workflow{Name = "Second-Ops"}}}, new Repo{Name = "ThirdRepo", Workflows = new List<Workflow>{new Workflow{Name = "CI-CD"}, new Workflow{Name = "Testers"}, new Workflow{Name = "Third-Ops"}}}};
    CollectionB.Repos = new List<Repo>{new Repo{Name = "FronEndUI", Workflows = new List<Workflow>{new Workflow{Name = "CD"}, new Workflow{Name = "UI-Tests"}, new Workflow{Name = "first-Op"}}}, new Repo{Name = "API", Workflows = new List<Workflow>{new Workflow{Name = "CI"}, new Workflow{Name = "Testing"}, new Workflow{Name = "second-Op"}}}, new Repo{Name = "VisualBasic", Workflows = new List<Workflow>{new Workflow{Name = "Deploy"}, new Workflow{Name = "Copy"}, new Workflow{Name = "third-Op"}}}};
    AllCollections.Add(CollectionA);
    AllCollections.Add(CollectionB);
    // Filter 
    string FilterString = "";  // string FilterString = "Copy" , should return  AllCollections > CollectionB > Repo VisualBasic > Workflow Deploy
    // Result should be List of collections > List of Repos > List of workflows
    List<Collection> result = AllCollections.SelectMany(c => c.Repos.Where(r => r.Name.Contains(FilterString.ToLower())).ToList().SelectMany(w => w.Workflows.Where(w => w.Name.Contains(FilterString)))).ToList();
    // Dont know how to show nested list in a table sorry
    // This is returning the workflows but not the parent Repo and Repo's Parent, The Collection



public class Collection
{
    public string Name { get; set; }

    public List<Repo> Repos { get; set; }
}

public class Repo
{
    public string Name { get; set; }

    public List<Workflow> Workflows { get; set; }
}

public class Workflow
{
    public string Name { get; set; }
}

See it here do.netfiddle

Answer 1

using this particular overload .

"Projects each element of a sequence to an IEnumerable, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein."

var result =
   AllCollections
       .SelectMany(collection => collection.Repos,
           (collection, repo) => new {collection, repo})
       .SelectMany(collectionAndRepo => collectionAndRepo.repo.Workflows,
           (collectionAndRepo, workflow) => new {collectionAndRepo, workflow})
       .Where(collectionAndRepoAndWorkflow =>
           collectionAndRepoAndWorkflow.collectionAndRepo.collection.Name
               .Contains(FilterString)
           || collectionAndRepoAndWorkflow.collectionAndRepo.repo.Name.Contains(
               FilterString)
           || collectionAndRepoAndWorkflow.workflow.Name.Contains(FilterString))
       .GroupBy(crw => crw.collectionAndRepo.collection.Name,
           (collectionName, repoAndWorkflow) =>
               new Collection
               {
                   Name = collectionName,
                   Repos = repoAndWorkflow.GroupBy(
                       rw => rw.collectionAndRepo.repo.Name,
                       (repoName, workflows) => new Repo()
                       {
                           Name = repoName,
                           Workflows = workflows.Select(w => new Workflow()
                               {Name = w.workflow.Name}).ToList()
                       }).ToList()
               }).ToList();