如何从行中获取 self 值以在 self eloquent model 中的另一个 select 查询中使用？

Question

I'm new at the laravel, Just started at few days ago and I already searched about this but nothing found about my question. For example... I have the offers and offers_prices table.

offers:

+----+-----------+
| id |   name    |
+----+-----------+
|  1 | Product 1 |
|  2 | Product 2 |
|  3 | Product 3 |
|  4 | Product 4 |
+----+-----------+

offers_prices:

+----+------------+-------+---------------------+
| id |  offer_id  | price |     created_at      |
+----+------------+-------+---------------------+
|  1 |          1 | 65.90 | 2020-12-17 16:00:00 |
|  2 |          1 | 64.99 | 2020-12-17 17:00:00 |
|  3 |          1 | 58.90 | 2020-12-17 18:00:00 |
|  4 |          1 | 60.99 | 2020-12-17 19:00:00 |
+----+------------+-------+---------------------+

To get the current offer price ( 60.99 ) I have created the function below to get it from a relationship eloquent model:

Models/Offer.php

public function price() {
    return parent::hasOne(OfferPrices::class)
        ->where("date", "<=", \Carbon\Carbon::now()->toDateTimeString())
        ->orderBy("date", "DESC")
        ->limit(1);
}

And now I want to get the most recent previous price but higher than current price like in the query below:

SELECT *
FROM offers_prices
WHERE offers_prices.offer_id = 1
AND
offers_prices.price > (
    SELECT offers_prices.price
    FROM offers_prices
    WHERE offers_prices.offer_id = 1
    AND offers_prices.date <= NOW()
    ORDER BY offers_prices.date DESC
    LIMIT 1
)
AND offers_prices.date <= NOW()
ORDER BY offers_prices.date DESC
LIMIT 1;

It means that the recent previous and higher than current price can't be 58.90 because it's lower than current (60.99) . Must be 64.99 . How can I do it? I have tried creating another function in the self eloquent model:

Models/Offer.php

public function prev_high_price() {
    return parent::hasOne(OfferPrices::class)
        ->where("date", "<=", \Carbon\Carbon::now()->toDateTimeString())
        ->where("price", ">", $this->price()->price)
        ->orderBy("date", "DESC")
        ->limit(1);
}

But it doesn't work..

Answer 1

You're using the hasOne relationship for a database relationship that looks more like a hasMany . Your Offers can have many Prices . Your table naming is outwith convention too as you're not using a pivot table but have named your offers_prices table as if it was.

Off topic to the question but relevant to your situation, it's advisable to not store currency values as floats or doubles. Store them as integers in the lowest denominator.

To answer your question, given the following two migrations:

Offers table migration

class CreateOffersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('offers', function (Blueprint $table) {
            $table->id();
            $table->timestamps();
            $table->string('name');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('offers');
    }
}

Prices table migration

class CreatePricesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('prices', function (Blueprint $table) {
            $table->id();
            $table->timestamps();
            $table->foreignId('offer_id');
            $table->integer('price');
            $table->foreign('offer_id')->references('id')->on('offers');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('prices');
    }
}

Define the following in your Offer model:

class Offer extends Model
{
    use HasFactory;

    public function prices()
    {
        return $this->hasMany(Price::class);
    }

    public function lastPrice()
    {
        return $this->prices()->orderBy('id', 'desc')->limit(1);
    }

    public function lastHighPrice()
    {
        return $this->prices()
            ->where('id', '<', $this->lastPrice()->first()->id)
            ->orderBy('price', 'desc')
            ->limit(1);
    }
}

Run your migration and database seeders (if you have any, otherwise just add data manually). In your terminal and whilst you're current working directory is your Laravel project, fire up tinker :

php artisan tinker

From inside tinker, you can now play around with your data and models.

// get a collection of all prices for the Offer with id 1
Offer::find(1)->prices

// get a collection with the last price for the offer with id 1
Offer::find(1)->lastPrice

// get a collection with the previous highest price for the offer with id 1
Offer::find(1)->lastHighPrice