framework/db/ActiveQueryTrait.php
public function with()
    {
        $with = func_get_args();
        if (isset($with[0]) && is_array($with[0])) {
            // the parameter is given as an array
            $with = $with[0];
        }

        if (empty($this->with)) {
            $this->with = $with;
        } elseif (!empty($with)) {
            foreach ($with as $name => $value) {
                if (is_int($name)) {
                    // repeating relation is fine as normalizeRelations() handle it well
                    $this->with[] = $value;
                } else {
                    $this->with[$name] = $value;
                }
            }
        }

        return $this;
    }
public function with()
    {
        $with = func_get_args();
        if (isset($with[0]) && is_array($with[0])) {
            // the parameter is given as an array
            $with = $with[0];
        }

        if (empty($this->with)) {
            $this->with = $with;
        } elseif (!empty($with)) {
            foreach ($with as $name => $value) {
                if (is_int($name)) {
                    // repeating relation is fine as normalizeRelations() handle it well
                    $this->with[] = $value;
                } else {
                    $this->with[$name] = $value;
                }
            }
        }

        return $this;
    }
Specifies the relations with which this query should be performed.

The parameters to this method can be either one or multiple strings, or a single array
of relation names and the optional callbacks to customize the relations.

A relation name can refer to a relation defined in [[modelClass]]
or a sub-relation that stands for a relation of a related record.
For example, `orders.address` means the `address` relation defined
in the model class corresponding to the `orders` relation.

The following are some usage examples:

```php
// find customers together with their orders and country
Customer::find()->with('orders', 'country')->all();
// find customers together with their orders and the orders' shipping address
Customer::find()->with('orders.address')->all();
// find customers together with their country and orders of status 1
Customer::find()->with([
'orders' => function (\yii\db\ActiveQuery $query) {
$query->andWhere('status = 1');
},
'country',
])->all();
```

You can call `with()` multiple times. Each call will add relations to the existing ones.
For example, the following two statements are equivalent:

```php
Customer::find()->with('orders', 'country')->all();
Customer::find()->with('orders')->with('country')->all();
```

@return $this the query object itself