Add support for querying relationship existence across databases to Eloquent

[sts-ryan-holton]

Hi 👋

I'm not sure whether this has been opened previously, but would appreciate the feedback on the idea to be implemented into the Laravel Framework.

We have a large web application that processes millions of records per day in MySQL.

Naturally, as a system grows, often is the case that new ideas and data storage solutions are implemented, as such, we decided to introduce a separate Postgres (Timescale DB) database for reporting and heavy log ingestion utilsing tpetry/laravel-postgresql-enhanced.

This means that we've set up another database connection to Postgres, and some models define a Postgres connection, others define a MySQL connection.

For the longest time, the official docs mention:

Eloquent does not currently support querying for relationship existence across databases. The relationships must exist within the same database.

But, currently Laravel is able to support regular with joins across connections.

It would be great if Laravel could add support for:

• withWhereHas
• whereHas

To the framework so we can do (where Post might be in MySQL and the comments relationship in Postgres):

// Retrieve posts with at least one comment containing words like code%...
$posts = Post::whereHas('comments', function (Builder $query) {
    $query->where('content', 'like', 'code%');
})->get();
 
// Retrieve posts with at least ten comments containing words like code%...
$posts = Post::whereHas('comments', function (Builder $query) {
    $query->where('content', 'like', 'code%');
}, '>=', 10)->get();

UPDATE

Open PR was closed at this time #60177