使用C# LINQ过滤三层嵌套集合并保留原层级结构的技术实现

Let's fix this nested filtering issue step by step. Your current implementation uses SelectMany which flattens the hierarchy, resulting in just a list of matching Workflow objects instead of preserving the parent Repo and Collection structure. Here's how to adjust the logic to keep the full nested hierarchy while filtering correctly:

Key Requirements Recap #

We need to:

• Match any level's Name property (Collection/Repo/Workflow) against the filter string (case-insensitive, based on your example)
• Keep only matching items and their parent hierarchy
• Maintain the original nested structure (List<Collection> → List<Repo> → List<Workflow>)

Correct LINQ Implementation #

First, normalize the filter string to lowercase to ensure consistent case-insensitive matching:

string filterLower = FilterString.ToLower();

Then, build the filtered hierarchy by iterating from the innermost layer outwards, and only retaining parent nodes if they either match the filter themselves or have child nodes that do:

var filteredCollections = AllCollections
    .Select(collection => new Collection
    {
        Name = collection.Name,
        // Filter Repos for this Collection
        Repos = collection.Repos
            .Select(repo => new Repo
            {
                Name = repo.Name,
                // Filter Workflows for this Repo
                Workflows = repo.Workflows
                    .Where(workflow => workflow.Name.ToLower().Contains(filterLower))
                    .ToList()
            })
            // Keep Repos that either match the filter OR have matching Workflows
            .Where(repo => repo.Name.ToLower().Contains(filterLower) || repo.Workflows.Any())
            .ToList()
    })
    // Keep Collections that either match the filter OR have matching Repos
    .Where(collection => collection.Name.ToLower().Contains(filterLower) || collection.Repos.Any())
    .ToList();

How This Works #

Let's walk through your example where FilterString = "Copy":

1. Workflow Layer: Only the Workflow named "Copy" in the "VisualBasic" Repo matches, so it's retained.
2. Repo Layer: The "VisualBasic" Repo is kept because it has a matching Workflow. All other Repos are filtered out since none of their Workflows match and their names don't include "Copy".
3. Collection Layer: CollectionB is kept because it has a retained Repo. CollectionA is filtered out entirely since none of its Repos or their Workflows match.

The final result is a List<Collection> containing only CollectionB, which contains only the "VisualBasic" Repo, which contains only the "Copy" Workflow—exactly the structure you expected.

Why Your Original Code Failed #

Your original code used SelectMany twice, which flattens the nested collections into a single sequence of Workflow objects. This discards all parent context (Repo and Collection), which is why you lost the hierarchy.

Entity Class Reference #

For completeness, here are the entity definitions you provided:

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; }
}

内容的提问来源于stack exchange，提问作者fuzzybear