Laravel Eloquent 获取关系字段

Question

I have a need to get a field from the relation from within the eloquent object.

I am using datatables to pass the eloquent object across for viewing.

I have an Model called Offices and a Model called Regions

Offices id name region -> belongsto regions

Regions id name

I need to get something like this: Offices.id, Offices.name, Regions.name

I have tried the below but that fails, how would I get the regions name in the get method?

$ReportData = Offices::with('region')->get(['id', 'name', 'region.name']);
return datatables()->eloquent($ReportData)

Answer 1

Eloquent relationships don't use joins, so you aren't able to select them in the Offices query.

$ReportData = Offices::with('region')->get(['id', 'name']);

Will execute a separate query to eager load all of the regions while allowing you to access each item's related region as a property:

$ReportData[0]->region->name

You can flatten this, use a map, or use a query with a join like Tim suggested if you desire.

You are able to limit the region data selected from the database by using a closure on with:

$ReportData = Offices::with(['region' => function($q) {
    $q->select('name');
})->get(['id', 'name']);

However, in most cases, I would consider this as over-optimization unless the region has a lot of data in other columns.

Answer 2

To limit your query results to specific columns, and include that of a relationship, you can use ->join() , coupled with ->select() :

$reportData = Offices::join("regions", "offices.region_id", "=", "regions.id")
->select("offices.id", "offices.name", "regions.name AS region_name")
->get();

Note: Had to guess on the join logic; could be inverse ( regions.office_id , etc)

Then, when accessing the contents of $reportData , you will only have access to three columns:

foreach($reportData AS $data){
  $data->id;
  $data->name;
  $data->region_name;
}

Answer 3

Since this is rated first on google and this is what I got when I ran this search, I think it should also contain the Laravel 8 answer. From the Laravel docs

You can specify columns when eager loading relationships like so:

$ReportData = Offices::with('region:id, name')->get(['id', 'name']);

Mind you, you should always include the id and foreign id columns in this specifications, otherwise it won't work.

So it should actually look something like this:

    $ReportData = Offices::with('region:id, name, office_id')->get(['id', 'name']);

Or whatever corresponds to your specific relationship.

Hopefully you find this useful, ye brave Laravel developer stumbling upon this!