Fetch Multiple Records with Joins in Laravel Eloquent - laravel

Question

I'm very new to using Laravel, thus to Eloquent. I am getting kind of confused about Eloquent's table relationships.
Now I understand how to implement simple joins, like the example in Laravel 4.2's documentation which for one-to-many relationships, where a comment belongs to one post, but a post can have many comments. They use this syntax to get the comments from one post:
Post::find(1)->comments;
Which, in MySQL, is probably like:
SELECT * FROM comments
JOIN posts ON posts.id=comments.post_id
WHERE posts.id=1
What if the results I'm trying to get is something like this that gets more than just one row:
SELECT * FROM comments
JOIN posts ON posts.id=comments.post_id
I know it doesn't make much sense based on the example I gave above. But how do I do it in Eloquent?
To give further details, what I'm actually trying to do is to display joined results from my two tables, assets and asset_classifications. An asset belongs to one asset_classification, and an asset_classification has many assets.
I'm trying to display a tabular data of assets which include their asset_classifications. In MySQL, it's something like this:
SELECT * FROM assets
JOIN asset_classifications ON asset_classifications.id=assets.classification_id
How can I perform it in Eloquent?

Answer 1

I guess you're a little too attached to SQL :) Try thinking outside of joins and queries an more in models and melattionships, because Laravel handles all the abstraction for you.
So you have an Asset model:
class Asset extends Eloquent
{
public function classification()
{
return $this->belongsTo('AssetClassification');
}
}
...and an AssetClassification mdoel:
class AssetClassification extends Eloquent
{
public function assets()
{
return $this->hasMany('Asset');
}
}
And now they are linked and you can do whatever you want. If you want to output all assets and their classification, no problem:
$assets = Asset::all();
foreach($assets as $asset)
{
echo "{$asset->name}" is classified as {$asset->classification}";
}
Or the other way around:
$classifications = AssetClassification::all();
foreach($classifications as $classification)
{
echo "{$classification->name} has the following assets:";
foreach($classification->assets as $asset)
{ ... }
}
As an array, this would look something like
[0] => [
'id' => 1
'name' => 'asset_name_1',
],
[1] => [
'id' => 2
'name' => 'asset_name_2',
],
You get the idea. The problem is, that you do a separate query on each iteration. That's why you should use eager loading to not also load all Assets but also their dependencies:
$assets = Asset::with('classification')->get();
Now you would have an array like this:
[0] => [
'id' => 1
'name' => 'asset_name_1',
'classification' => AssetClassiciation-Object
],
[1] => [
'id' => 2
'name' => 'asset_name_2',
'classification' => AssetClassiciation-Object
],
So now you can loop through assets and their classification without making any further SQL-queries.