Solving the PSCustomObject Overwrite Issue in PowerShell

Learn how to effectively use `PSCustomObject` in PowerShell when comparing arrays and avoid common pitfalls that lead to overwriting data.
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Understanding the Issue with PSCustomObject in PowerShell

As a new PowerShell developer, you may encounter various challenges, particularly when handling data structures like arrays or custom objects. One such common issue arises when using PSCustomObject to store results from nested loops. In this guide, we will explore a specific problem where PSCustomObject only retains the last written value, and we will provide a step-by-step solution to ensure you can effectively capture all desired outputs.

The Problem

In your PowerShell script, you are comparing two arrays through a nested loop, looking for matches and intending to populate a third array with results stored in PSCustomObject. However, you noticed that after multiple matches, your PSCustomObject only contains a single row of data instead of multiple rows. This indicates that each update of the PSCustomObject is overwriting the previous results.

The Source of Confusion

Let's break down the situation:

You are creating a new PSCustomObject inside the inner loop whenever a match is found.

However, each time a match is found, the variable intended to store results is being overwritten rather than accumulating results.

This can be frustrating, especially when trying to analyze your code logic, as it appears to work in finding matches, yet doesn’t store them as expected.

The Solution

The solution is straightforward once the mechanism of PowerShell's PSCustomObject output mechanics is understood. Instead of individual updates, we will leverage PowerShell’s ability to capture output objects effectively.

Steps for Implementing the Correct Approach

Capture Output Directly:
Modify your existing script to capture the objects directly into a variable without needing to pre-create an empty array. This lets PowerShell handle output collection automatically.

Adjust Your Loop Structure:
Ensure that your object creation logic is maintained inside the loops as needed, but change how you are storing this data.

Here’s the refined version of your script:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes and Their Benefits:

Removed Initialization: No need to create an array or ArrayList before the loop.

Direct Output: This captures any PSCustomObject created in the loop and aggregates the results into the $result variable without overwriting them.

Conclusion

Using PSCustomObject effectively can initially seem daunting, especially when it comes to managing output across nested loops. However, by allowing PowerShell to automatically collect objects, you can avoid common pitfalls like overwriting values.

This method not only simplifies your code but also ensures that you can easily check for all matches found during execution. As you continue to explore PowerShell, practicing this approach will enhance your coding efficiency and help you leverage its powerful features more effectively.

With this adjustment, your PSCustomObject should now reflect the multiple rows of data as intended. Happy coding!