How to check one to many tables in laravel

In Laravel, we often need to use relational databases to store and manage data, and one-to-many relationships are the most common one. A one-to-many relationship refers to a relationship in which a model has multiple associated models. It is usually used to implement some common business scenarios, such as one user corresponding to multiple orders or one course corresponding to multiple students.

In Laravel, we can use Eloquent ORM to implement one-to-many relationship query. Below I will introduce in detail how to use the Eloquent model in Laravel to query the one-to-many relationship between three tables.

1. Design three tables

First, we need to design three tables, namely the main table, the sub-table and the sub-table foreign key association table. The following is the design of the sample table:

Main table: users

id	name	email
1	Tom	tom@laravel.com
2	Jerry	jerry@laravel.com
3	Bob	bob@laravel.com

Sub table: orders

id	order_no	user_id
1	1001	1
2	1002	2
3	1003	3
4	1004	1

Sub-table foreign key related table: order_items

##54grape

id	order_id	product_name
1	1	apple
2	1	banana
3	2	pear
4	4	orange

Create Laravel model

In Laravel, we need to create three models, corresponding to three tables respectively. When creating a model, we need to define the relationships between models.

Main table model: User

class User extends Model
{
    public function orders()
    {
        return $this->hasMany(Order::class);
    }
}

Sub table model: Order

class Order extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }

    public function items()
    {
        return $this->hasMany(OrderItem::class);
    }
}

Sub table foreign key related table model: OrderItem

class OrderItem extends Model
{
    public function order()
    {
        return $this->belongsTo(Order::class);
    }
}

Query One-to-many relationship

In Laravel, we can use Eloquent ORM to implement one-to-many relationship query. The following is a code example to query all orders of a user and all order items placed under them:

$user = User::find(1);

foreach ($user->orders as $order) {
    echo $order->order_no;

    foreach ($order->items as $item) {
        echo $item->product_name;
    }
}

The above code will output all orders of user Tom and all order items placed under them.

We can also directly use Eloquent's associated preloading method to query a user, his orders and all order items:

$user = User::with('orders.items')->find(1);

foreach ($user->orders as $order) {
    echo $order->order_no;

    foreach ($order->items as $item) {
        echo $item->product_name;
    }
}

The above code will output all orders and orders of user Tom For all line items under it, this method has better performance than the above method.

Summary

In Laravel, we can use Eloquent ORM to implement one-to-many relationship query very conveniently. As long as the relationship is defined in the model, you can easily obtain all the associated data of the specified model. At the same time, we can also use the associated preloading method to optimize query performance and make our applications more efficient and stable.

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