Eloquent Custom Relations: Pivots, HasManyThrough & Raw Joins | Mohamed Said [ ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MH.png) Mohamed Said Laravel Backend Engineer ](https://www.msaied.com) [ Home ](https://www.msaied.com) [ Projects ](https://www.msaied.com/projects) [ Articles ](https://www.msaied.com/articles) [ Certificates ](https://www.msaied.com/certificates) [ Contact ](https://www.msaied.com#contact-section) [ ](https://github.com/EG-Mohamed) [ Home ](https://www.msaied.com) [ Projects ](https://www.msaied.com/projects) [ Articles ](https://www.msaied.com/articles) [ Certificates ](https://www.msaied.com/certificates) [ Contact ](https://www.msaied.com#contact-section) [ home ](https://www.msaied.com) [ articles ](https://www.msaied.com/articles) Eloquent Custom Relations: Polymorphic Pivots, HasManyThrough Tricks, and Raw Join Relations On this page 1. [ Why Eloquent's Built-in Relations Are Not Always Enough ](#why-eloquents-built-in-relations-are-not-always-enough) 2. [ Case 1: A Raw-Join Relation for Denormalised Reporting Tables ](#case-1-a-raw-join-relation-for-denormalised-reporting-tables) 3. [ Case 2: HasManyThrough Across a Polymorphic Pivot ](#case-2-hasmanythrough-across-a-polymorphic-pivot) 4. [ Case 3: Polymorphic Pivot with Extra Columns ](#case-3-polymorphic-pivot-with-extra-columns) 5. [ Eager Loading Gotchas ](#eager-loading-gotchas) 6. [ Takeaways ](#takeaways) ![Eloquent Custom Relations: Polymorphic Pivots, HasManyThrough Tricks, and Raw Join Relations](https://cdn.msaied.com/210/b47272214946c6adcd02ddf74b7df816.png) #laravel #eloquent #database #orm Eloquent Custom Relations: Polymorphic Pivots, HasManyThrough Tricks, and Raw Join Relations ============================================================================================== 16 Jun 2026 3 min read ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MJ.jpg) Mohamed Said Table of contents 1. [ 01 Why Eloquent's Built-in Relations Are Not Always Enough ](#why-eloquents-built-in-relations-are-not-always-enough) 2. [ 02 Case 1: A Raw-Join Relation for Denormalised Reporting Tables ](#case-1-a-raw-join-relation-for-denormalised-reporting-tables) 3. [ 03 Case 2: HasManyThrough Across a Polymorphic Pivot ](#case-2-hasmanythrough-across-a-polymorphic-pivot) 4. [ 04 Case 3: Polymorphic Pivot with Extra Columns ](#case-3-polymorphic-pivot-with-extra-columns) 5. [ 05 Eager Loading Gotchas ](#eager-loading-gotchas) 6. [ 06 Takeaways ](#takeaways) Why Eloquent's Built-in Relations Are Not Always Enough ------------------------------------------------------- Eloquent ships with nine relation types, but real-world schemas rarely fit neatly into any of them. You end up writing `DB::select` calls, appending attributes in `getXAttribute`, or firing N+1 queries because the "right" relation doesn't exist. The fix is almost always a custom relation class — and it's less work than it looks. --- Case 1: A Raw-Join Relation for Denormalised Reporting Tables ------------------------------------------------------------- Imagine a `metrics` table that stores pre-aggregated rows keyed by `entity_type` and `entity_id`. You want `$post->metrics` to behave like a first-class relation — eager-loadable, constrainable, and serialisable. Extend `Illuminate\Database\Eloquent\Relations\Relation` directly: ```php namespace App\Relations; use Illuminate\Database\Eloquent\Builder; use Illuminate\Database\Eloquent\Collection; use Illuminate\Database\Eloquent\Model; use Illuminate\Database\Eloquent\Relations\Relation; class HasMetrics extends Relation { public function addConstraints(): void { if (static::$constraints) { $this->query ->where('entity_type', $this->parent->getMorphClass()) ->where('entity_id', $this->parent->getKey()); } } public function addEagerConstraints(array $models): void { $this->query ->where('entity_type', $this->parent->getMorphClass()) ->whereIn('entity_id', $this->getKeys($models)); } public function initRelation(array $models, $relation): array { foreach ($models as $model) { $model->setRelation($relation, $this->related->newCollection()); } return $models; } public function match(array $models, Collection $results, $relation): array { foreach ($models as $model) { $matched = $results->where('entity_id', $model->getKey()); $model->setRelation($relation, $matched->values()); } return $models; } public function getResults(): Collection { return $this->query->get(); } } ``` Register it on the model: ```php public function metrics(): HasMetrics { return new HasMetrics( (new Metric)->newQuery(), $this ); } ``` Now `Post::with('metrics')->get()` works without a single extra query. --- Case 2: HasManyThrough Across a Polymorphic Pivot ------------------------------------------------- `HasManyThrough` requires concrete foreign keys on the intermediate table. When that table is a polymorphic pivot (`taggables`, `mediables`), the standard relation breaks because it can't scope the intermediate join to a single `*_type`. The cleanest fix is a scoped `hasManyThrough` using a custom intermediate model: ```php // Intermediate model scoped to one morph type class PostTaggable extends Model { protected $table = 'taggables'; protected static function booted(): void { static::addGlobalScope('type', fn (Builder $q) => $q->where('taggable_type', Post::class) ); } } // On the Post model public function tags(): HasManyThrough { return $this->hasManyThrough( Tag::class, PostTaggable::class, 'taggable_id', // FK on taggables -> posts 'id', // FK on tags 'id', // local key on posts 'tag_id' // local key on taggables ); } ``` The global scope on `PostTaggable` ensures the join is always filtered by `taggable_type`, making eager loading safe. --- Case 3: Polymorphic Pivot with Extra Columns -------------------------------------------- When a polymorphic pivot carries extra data (e.g., `order`, `metadata`), `MorphToMany` supports `withPivot()` just like `BelongsToMany`: ```php public function media(): MorphToMany { return $this->morphToMany(Medium::class, 'mediable') ->withPivot(['order', 'caption']) ->orderByPivot('order'); } ``` Access pivot data via `$medium->pivot->caption`. For typed pivot models, swap to `using(MediablePivot::class)` and cast columns there — keeping the domain logic off the parent model. --- Eager Loading Gotchas --------------------- - **`addEagerConstraints` must not call `addConstraints` logic** — the parent key set replaces the single-model constraint entirely. - **`getKeys()` strips nulls** — guard against models without a primary key before calling it. - Custom relations are not automatically recognised by `Model::$with`; declare them explicitly. --- Takeaways --------- - Extending `Relation` directly gives you full control over eager loading without raw DB calls. - Scoped intermediate models solve the polymorphic `HasManyThrough` problem cleanly. - `withPivot` + `using` keeps extra pivot data typed and testable. - Custom relations serialise, cache, and constrain exactly like built-in ones. - The four methods to implement are `addConstraints`, `addEagerConstraints`, `initRelation`, and `match`. Found this useful? [ ](https://twitter.com/intent/tweet?url=https%3A%2F%2Fwww.msaied.com%2Farticles%2Feloquent-custom-relations-polymorphic-pivots-hasmanythrough-tricks-and-raw-join-relations&text=Eloquent+Custom+Relations%3A+Polymorphic+Pivots%2C+HasManyThrough+Tricks%2C+and+Raw+Join+Relations) [ ](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fwww.msaied.com%2Farticles%2Feloquent-custom-relations-polymorphic-pivots-hasmanythrough-tricks-and-raw-join-relations) Frequently Asked Questions ---------------------------- 3 questions Q01 Can custom Eloquent relations be used inside `with()` for eager loading? Yes. As long as you implement `addEagerConstraints`, `initRelation`, and `match` correctly, Laravel's eager loader treats your custom relation identically to built-in ones. Q02 Why does HasManyThrough fail with polymorphic pivot tables? HasManyThrough joins the intermediate table without a `*_type` constraint, so it returns rows for all morph types. Scoping the intermediate model with a global scope that filters by the correct morph type fixes this without changing the relation signature. Q03 Is there a performance cost to custom relation classes? No measurable overhead beyond what any relation incurs. The query count is identical to a built-in relation when eager loading is used correctly. Continue reading More Articles --------------- [ View all ](https://www.msaied.com/articles) [ ![Laravel Telescope Alternatives: Building a Lightweight Request Inspector with Middleware](https://cdn.msaied.com/216/9b6d240010b80483f072902dafcd216c.png) laravel middleware debugging ### Laravel Telescope Alternatives: Building a Lightweight Request Inspector with Middleware Telescope is powerful but heavy for production. Learn how to build a focused, low-overhead request inspector u... ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MJ.jpg) Mohamed Said 16 Jun 2026 1 min read Read ](https://www.msaied.com/articles/laravel-telescope-alternatives-building-a-lightweight-request-inspector-with-middleware) [ ![RAG Pipelines in Laravel: Chunking, Embedding, and Retrieval with pgvector](https://cdn.msaied.com/215/e037e13535aa77822f879ee829ec3f68.png) laravel ai pgvector ### RAG Pipelines in Laravel: Chunking, Embedding, and Retrieval with pgvector Build a production-ready Retrieval-Augmented Generation pipeline in Laravel using pgvector, OpenAI embeddings,... ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MJ.jpg) Mohamed Said 16 Jun 2026 3 min read Read ](https://www.msaied.com/articles/rag-pipelines-in-laravel-chunking-embedding-and-retrieval-with-pgvector) [ ![Laravel Pest: Architecture Tests, Mutation Testing, and Type Coverage in CI](https://cdn.msaied.com/214/0d4822fa8ee1765d0689e387dd849d92.png) laravel pest testing ### Laravel Pest: Architecture Tests, Mutation Testing, and Type Coverage in CI Go beyond feature tests. Learn how to enforce architectural rules, catch logic gaps with mutation testing, and... ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MJ.jpg) Mohamed Said 16 Jun 2026 4 min read Read ](https://www.msaied.com/articles/laravel-pest-architecture-tests-mutation-testing-and-type-coverage-in-ci) [ ![Mohamed Said](https://cdn.msaied.com/01KT78WE565VEMM3PSNQAAB0MH.png) Mohamed Said Laravel Backend Engineer ](https://www.msaied.com)Senior Backend Engineer specializing in Laravel, scalable SaaS platforms, APIs, and cloud infrastructure. I build secure, high-performance web applications that help businesses grow. Explore - [Home](https://www.msaied.com) - [Projects](https://www.msaied.com/projects) - [Articles](https://www.msaied.com/articles) - [Certificates](https://www.msaied.com/certificates) - [Contact](https://www.msaied.com#contact-section) Connect - [ hello@msaied.com ](mailto:hello@msaied.com) - [ +20 109 461 9204 ](tel:+201094619204) © 2026 Mohamed Said. All rights reserved. [ ](https://github.com/EG-Mohamed) [ ](https://www.linkedin.com/in/msaiedm/) [ ](https://wa.me/201094619204) [ ](mailto:hello@msaied.com) [ ](https://drive.google.com/file/u/0/d/1MF20IPRJyzfy32mhEutjL5EpSls0w2Q8/view)