从相关表中获取第二高的日期

Question

I am trying to fetch the second highest date from a relation-table in with Eloquent Laravel 6.

MoodTable
id    animal_id  date          mood
1     1          2019-12-14    happy
2     1          2019-12-11    drunk
3     1          2019-12-13    sad

AnimalTable
id    name
1     Dog

So for example, I want to be able to query: "Today Dog is happy. Prevously to that he was Drunk.

To fetch the highest I use:

return $this->hasMany('App\AnimalMood', 'animal_id')->select(DB::raw('
                    mood,
                    animal_id,
                    MAX(date) as max_date,  
                    '))
                 ->groupBy('stock_id');

However, when it comes to seconed highest date... I'm out...

I have looked at How to return second newest record in SQL? for some answers,but not been able to put that in a relationship senario nor translate it to Eloquent.

Ideally, I would like to run Animal::with('moodPrevious')->get() and Animal::find(1)->moodPrevious from my controller...

Answer 1

I would change the relationship and grab all of the related models to your Animal model when you query for it.

return $this->hasMany('App\\AnimalMood', 'animal_id');

Below returns the animals with the moods pre-sorted.

$animals = Animal::with(['mood' => function($q){
               $q->orderByDesc('date');
           }])->get();

Laravel offers a lot of collection methods that work well with related models. I would use the callback you can provide to first() in order to get the mood you want on the model. You probably already have the specific model you want, either by foreaching over the above collection or something similar. The relation will be a collection instance so we use the collection method to get the mood desired.

$previousMood = $animal->mood->first(function($value, $key){
    return $key == 1 // You can use whatever here, this will return the second item on the relation, or the previous mood.
});

See https://laravel.com/docs/5.8/collections#method-first for a reference.

Answer 2

I think this would work

return $this->hasMany('App\AnimalMood', 'animal_id')
    ->select(
        DB::raw('
            mood,
            animal_id,
            MAX(date) as max_date,  
        ')
    )
    ->where(
        DB::raw("
            date = (
                SELECT 
                    MAX(date) 
                FROM animal_moods 
                WHERE date < (
                    SELECT 
                        MAX(date) 
                    FROM 
                    animal_moods
                )
            )
        ")
    )
    ->groupBy('stock_id');