How to understand ORM in Laravel

                                                       

What is ORM

ORM，全称 Object-Relational Mapping（对象关系映射），它的作用是在关系型数据库和业务实体对象之间作一个映射，
这样，我们在操作具体的业务对象时，就不需要再去和复杂的SQL语句打交道，只需简单的操作对象的属性和方法即可。

ORM implementation method

两种最常见的实现方式是 ActiveRecord 和 DataMapper (laravel 中使用的是前者)

Let’s first understand the two magic functions __call() and __callStatic()

class Test{
    //动态调用的时候 没有找到此函数 则执行__call() 方法
    public function __call($method, $parameters){
        echo 22222222222;
        return (new Rest)->$method(...$parameters);
    }

    //静态调用的时候 没有找到此函数 则执行__callStatic()方法
    public static function __callStatic($method, $parameters){
        echo 1111111111;
        return (new static)->$method(...$parameters);
    }}class Rest{
  public function foo($name , $age){
  echo 333;
  dump($name,$age);
  }}
  //先调用了__callStatic(), 在调用__call(), 然后调用 foo();
  Test::foo('张三',17);  
  //只调用了 __call(), 然后调用 foo();
  (new Test())->foo('李四',16);die;

After understanding the previous two magic functions, we will understand the difficulties in laravel Eloqument ORM. Let’s take a look. The source code in Model

/**
 * Handle dynamic method calls into the model. * * @param string $method
  * @param array $parameters
  * @return mixed
 */public function __call($method, $parameters){
 if (in_array($method, ['increment', 'decrement'])) {
      return $this->$method(...$parameters);
  }
  return $this->newQuery()->$method(...$parameters);}
  /**
 * Handle dynamic static method calls into the method. * * @param string $method
  * @param array $parameters
  * @return mixed
 */public static function __callStatic($method, $parameters)
 {
 return (new static)->$method(...$parameters);
 }

new static returns the instance of the caller, new self() returns its own instance
When using eloqument to query

$list = Politician::where('party_id', 1)->count();

where method is not in the Model The callStatic() function will be executed first to obtain the App\Models\Politician instance, and then call() will be executed to find where() count() and other methods in the instance returned by $this->newQuery().
Take a closer look at the instance returned by the newQuery() method. After understanding these two magic functions, the difficulty of implementing ORM in Laravel has been overcome.

The query constructor in laravel

$list = DB::table('categoty')->get();

Eloquent ORM actually encapsulates the query construction, making it easier to operate. If you are interested in the source code of the query constructor, you can take a look, thank you.

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