About using join and joinwith for multi-table association query in Yii2

This article mainly introduces the relevant information of multi-table related queries (join, joinwith) in Yii2. It is very good and has reference value. Friends in need can refer to it

Table structure

Now there are customer table, order table, book table, author table,

Customer table Customer (id customer_name)
Order table Order (id order_name customer_id book_id)
Book table(id book_name author_id)
Author table(id author_name)

Model definition

The following is For the definitions of these four models, only the relationships among them are written

Customer

class Customer extends \yii\db\ActiveRecord
{
// 这是获取客户的订单，由上面我们知道这个是一对多的关联，一个客户有多个订单
public function getOrders()
{
// 第一个参数为要关联的子表模型类名，
// 第二个参数指定 通过子表的customer_id，关联主表的id字段
return $this->hasMany(Order::className(), ['customer_id' => 'id']);
}
}

Order

class Order extends \yii\db\ActiveRecord
{
// 获取订单所属用户
public function getCustomer()
{
//同样第一个参数指定关联的子表模型类名
//
return $this->hasOne(Customer::className(), ['id' => 'customer_id']);
}
// 获取订单中所有图书
public function getBooks()
{
//同样第一个参数指定关联的子表模型类名
//
return $this->hasMany(Book::className(), ['id' => 'book_id']);
}
}

Book

class Book extends \yii\db\ActiveRecord
{
// 获取图书的作者
public function getAuthor()
{
//同样第一个参数指定关联的子表模型类名
return $this->hasOne(Author::className(), ['id' => 'author_id']);
}
}

Author

class Autor extends \yii\db\ActiveRecord
{
}

hasMany, hasOne uses tables in

Yii2 There are two types of associations, which are used to specify the association between two models.

One-to-many: hasMany

One-to-one: hasOne

Return results: The return results of these two methods are yii\db\ ActiveQuery object

The first parameter: the class name of the associated model.

The second parameter: is an array, where the key is the attribute in the associated model and the value is the attribute in the current model.

Associated use

Now we get all the order information of a customer

// 获取一个客户信息
$customer = Customer::findOne(1);
$orders = $customer->orders; // 通过在Customer中定义的关联方法（getOrders()）来获取这个客户的所有的订单。

The above two lines of code will generate the following sql statement

SELECT * FROM customer WHERE id=1;
SELECT * FROM order WHERE customer_id=1;

Associated result cache

If the customer's order changes, we will call again

$orders = $customer->orders;

When you get the order again, you will find that there is no change. The reason is that the database will only be queried when $customer->orders is executed for the first time, and the results will be cached, and sql will not be executed during subsequent queries.

So what if I want to execute sql again? You can execute

unset($customer->orders);
$customer->orders;

and then you can get the data from the database.

Define multiple associations

Similarly, we can also define multiple associations in Customer.
If the total number of orders is returned greater than 100.

class Customer extends \yii\db\ActiveRecord
{
public function getBigOrders($threshold = 100)
{
return $this->hasMany(Order::className(), ['customer_id' => 'id'])
->where('subtotal > :threshold', [':threshold' => $threshold])
->orderBy('id');
}
}

The two associated access methods

As above, if you use

$customer->bigOrders

will get all orders greater than 100. If you want to return orders greater than 200, you can write like this

$orders = $customer->getBigOrders(200)->all();

As you can see from the above, there are two ways to access an association

If called as a function, an ActiveQuery object ($customer->getOrders()->all()) will be returned.

If called as an attribute, the model will be returned directly. The result of ($customer->orders)

with looks at the following code, which is to take a customer's order

// 执行sql语句: SELECT * FROM customer WHERE id=1
$customer = Customer::findOne(1);
//执行sql：SELECT * FROM order WHERE customer_id=1
$orders1 = $customer->orders;
//这个不会执行sql，直接使用上面的缓存结果
$orders2 = $customer->orders;

If now We need to take out 100 users, and then access each user's order. From the above understanding, we may write the following code

// 执行sql语句: SELECT * FROM customer LIMIT 100
$customers = Customer::find()->limit(100)->all();
foreach ($customers as $customer) {
// 执行sql: SELECT * FROM order WHERE customer_id=...
$orders = $customer->orders;
// 处理订单。。。
}

However, if we really want If written like this, sql will be executed once in each loop of foreach to query the data in the database. Because each $customer object is different.

In order to solve the above problem, you can use yii\db\ActiveQuery::with().

The width parameter is the name of the relationship, which is the getOrders defined in the model, the orders and customer in getCustomer

// 先执行sql: SELECT * FROM customer LIMIT 100;
// SELECT * FROM orders WHERE customer_id IN (1,2,...)
$customers = Customer::find()->limit(100)
->with('orders')->all();
foreach ($customers as $customer) {
// 在这个循环的时候就不会再执行sql了
$orders = $customer->orders;
// ...handle $orders...
}

If Select is used to specify the returned columns. Be sure to ensure that the returned columns contain the associated fields of the associated model, otherwise the Model

$orders = Order::find()->select(['id', 'amount'])->with('customer')->all();
// $orders[0]->customer 的结果将会是null
// 因为上面的select中没有返回所关联的模型（customer）中的指定的关联字段。
// 如果加上customer_id，$orders[0]->customer就可以返回正确的结果
$orders = Order::find()->select(['id', 'amount', 'customer_id'])->with('customer')->all();

## of the associated table will not be returned.

#Add filter conditions to with

Query an order with more than 100 customers

//首先执行sql： SELECT * FROM customer WHERE id=1
$customer = Customer::findOne(1);
// 再执行查询订单的sql语句：SELECT * FROM order WHERE customer_id=1 AND subtotal>100
$orders = $customer->getOrders()->where('subtotal>100')->all();

Query 100 customers, each customer’s total order is greater than 100

// 下面的代码会执行sql语句: 
// SELECT * FROM customer LIMIT 100
// SELECT * FROM order WHERE customer_id IN (1,2,...) AND subtotal>100
$customers = Customer::find()->limit(100)->with([
'orders' => function($query) {
$query->andWhere('subtotal>100');
},
])->all();

The width parameter here is an array, and the key is associated Name, value is the callback function.

That is to say, for the ActiveQuery returned by the orders association, execute $query->andWhere('subtotal>100');

Use joinWith to perform table processing Association

We all know that we can use join on to write associations between multiple tables. First look at the declaration of joinWit in yii2

joinWith( $with, $eagerLoading = true, $joinType = 'LEFT JOIN' )

$with The data type is a string or an array. If it is a string, it is associated with the one defined in the model. Name (can be a child association).

If it is an array, the key is the association defined in the getXXX format in the model, and the value is the further callback operation for this association.

$eagerLoading Whether to load the data of the model associated in $with.

$joinType 联接类型，可用值为：LEFT JOIN、INNER JOIN，默认值为LEFT JOIN

// 订单表和客户表以Left join的方式关联。
// 查找所有订单,并以客户 ID 和订单 ID 排序
$orders = Order::find()->joinWith('customer')->orderBy('customer.id, order.id')->all();
// 订单表和客户表以Inner join的方式关联
// 查找所有的订单和书
$orders = Order::find()->innerJoinWith('books')->all();
// 使用inner join 连接order中的 books关联和customer关联。
// 并对custmer关联再次进行回调过滤：找出24小时内注册客户包含书籍的订单
$orders = Order::find()->innerJoinWith([
'books',
'customer' => function ($query) {
$query->where('customer.created_at > ' . (time() - 24 * 3600));
}
])->all();
// 使用left join连接 books关联，books关联再用left join 连接 author关联
$orders = Order::find()->joinWith('books.author')->all();

在实现上，Yii 先执行满足JOIN查询条件的SQL语句，把结果填充到主模型中， 然后再为每个关联执行一条查询语句， 并填充相应的关联模型。

// Order和books关联 inner join ,但不获取books关联对应的数据
$orders = Order::find()->innerJoinWith('books', false)->all();

On条件

在定义关联的时候还可以指定on条件

class User extends ActiveRecord
{
public function getBooks()
{
return $this->hasMany(Item::className(), ['owner_id' => 'id'])->onCondition(['category_id' => 1]);
}
}

在joinWith中使用

//先查询主模型（User）的数据， SELECT user.* FROM user LEFT JOIN item ON item.owner_id=user.id AND category_id=1
// 然后再根据关联条件查询相关模型数据SELECT * FROM item WHERE owner_id IN (...) AND category_id=1
// 这两个在查询的过程中都使用了 on条件。
$users = User::find()->joinWith('books')->all();

如果没有使用join操作，即使用的是with 或者 直接以属性来访问关联。这个时候on条件会作为where 条件。

// SELECT * FROM user WHERE id=10
$user = User::findOne(10);

总结

首先需要在模型中定义好关联（如getOrders中的Orders为一个关联）

然后在with或者joinWith中使用在模型中定义的关联。

其中在使用关联的时候还可以指定回调方法。

再有就是可以给关联、with、joinWith指定where或者on条件

这一部分其实非常多，也有点乱，有些功能没说说完，如三个表关联、逆关联等。

最基本的操作也就大体是这些。如果还有哪个地方想了解的，可以回帖交流。

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