GreatlyUnknown seeks advice on writing a LINQ query to retrieve questions with selected options from a nested questionnaire structure, sparking a discussion about effective usage of SelectMany in C#.

LINQ Query to Select Questions with Selected Options in Nested Questionnaire Structure

Author: GreatlyUnknown

Problem Statement

A questionnaire has the following nested structure:

  • Categories
    • Sections
      • Questions
        • Options (each can be selected or not)

The goal is to collect all Question objects with at least one selected Option, avoiding deeply nested foreach loops in favor of a LINQ-based approach.

Example LINQ Solutions

Participants suggested using SelectMany and Where:

var questionsWithAtLeastOneSelectedOption =
    categories
        .SelectMany(c => c.Sections)
        .SelectMany(s => s.Questions)
        .Where(q => q.Options.Any(o => o.IsSelected));

Or, more succinctly (if query syntax is preferred):

var questionsWithSelected =
    from c in categories
    from s in c.Sections
    from q in s.Questions
    where q.Options.Any(o => o.IsSelected)
    select q;

Key Notes

  • SelectMany flattens nested collections, making it effective for traversing multi-level data.
  • Where allows filtering to questions that meet the criteria (at least one option selected).

Community Takeaways

  • Use of SelectMany is standard for this kind of nested selection in C#.
  • Remembering key LINQ operators helps keep code concise and readable.
  • Some participants advocate using AI tools for such queries, though traditional community support is still valued.

Summary

If working with a nested questionnaire structure in C#, use SelectMany and Where to efficiently filter for questions with selected options, avoiding cumbersome nested loops.

References:

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