Laravel flatten and pluck from multidimensional collection
Stefan Bogdanescu
Founder & Senior Architect · 2026-06-29
# Laravel Flatten and Pluck from Multidimensional Collections: Unlocking Nested Data Extraction
As developers working with relational data in Laravel, we frequently encounter scenarios where Eloquent relationships return deeply nested collections. While methods like `pluck()` and `flatten()` are powerful for simple one-level arrays, extracting a truly flat list of IDs from multiple levels of nested relationships requires a more sophisticated approach. This guide will walk you through the problem presented—extracting all `id`s from a multi-level hierarchy—and demonstrate the most effective ways to achieve this without resorting to cumbersome `foreach` loops.
## The Challenge: Deeply Nested Eloquent Data
The example provided illustrates a common data structure resulting from eager loading complex relationships:
```php
// Result of $children->childrens()->get()
[
{
"id": 10,
"father_id": 2,
"childrens": [ /* ... nested children ... */ ]
},
// ... more results
]
```
The goal is to transform this structure into a simple, flat array of IDs: `[10, 54, 61, 21]`. Standard collection methods like `pluck('id')` only extract the IDs from the *immediate* level of the primary collection, leaving the nested relationships intact.
## Why Simple `pluck()` Fails Here
When you call `pluck('id')` on the main result set, Laravel simply returns the `id`s of the top-level parent objects (in this case, the IDs of the records where the relationship was initiated). It does not recursively dive into the nested `childrens` arrays to collect every ID. This is because Eloquent's collection methods operate on the structure provided by the database query result, and they don't inherently know how to traverse arbitrary depth unless explicitly told to do so.
To solve this, we need a method that performs a recursive traversal of the nested structures before extraction.
## The Solution: Recursive Flattening with Collection Methods
Since standard Laravel collection methods don't provide a direct, built-in recursive `flatten` function for arbitrarily deep nesting within Eloquent results, the most robust solution involves leveraging PHP’s capabilities alongside collection manipulation techniques. We need to iterate through every level of the hierarchy.
Here is a practical approach using nested iteration combined with `collect()` to achieve the desired flat array:
```php
use Illuminate\Support\Collection;
// Assuming $children is the Eloquent Collection result from your query
$flatIds = collect();
foreach ($children as $child) {
// 1. Add the current ID (the parent level)
$flatIds->push($child->id);
// 2. Recursively check the nested 'childrens' collection
if ($child->childrens) {
foreach ($child->childrens as $grandchild) {
// Add the grandchild IDs found at this deeper level
$flatIds->push($grandchild->id);
}
}
}
// The result is now a flat array: [10, 54, 61, 21, ...]
```
### A More Functional Approach (Using `flatMap` or Nested Mapping)
For more complex, deeply nested scenarios, especially when dealing with arbitrary depth, functional programming methods can offer cleaner syntax than manual loops. While Laravel collections don't natively expose a recursive `flatten` that handles deep nesting across relationships directly, you can achieve similar results by mapping and flattening the resulting arrays:
```php
$allIds = $children->map(function ($child) {
// Get the current ID
$ids = [$child->id];
// Recursively collect IDs from nested children
if ($child->childrens) {
foreach ($child->childrens as $grandchild) {
$ids = array_merge($ids, $grandchild->id);
// For deeper nesting, you would recursively call this logic here.
}
}
return $ids;
})->flatten()->values(); // Flatten the resulting array of arrays into a single list
```
The key takeaway here is that when dealing with deeply nested data from Eloquent relationships, treat the collection as raw data during processing. While Eloquent excels at querying and relationship management (as demonstrated by the structure in documentation on [laravelcompany.com](https://laravelcompany.com)), final data manipulation often requires standard PHP iteration or functional collection methods to achieve true structural flattening.
## Conclusion
Extracting a flat array of IDs from multi-dimensional Eloquent collections is a common data wrangling task. While simple chaining like `pluck()` is insufficient for deep nesting, the solution lies in employing recursive logic—either through explicit nested loops or advanced collection manipulation techniques applied after the initial query. By understanding how to traverse these nested structures, you can efficiently transform complex relational data into the simple, flat arrays needed for final presentation.