Fixes #2415: Added support for inverse relations

docs/guide/active-record.md

@@ -413,6 +413,96 @@ $customers = Customer::find()->limit(100)->with([
 ```
 
 
+Inverse Relations
+-----------------
+
+Relations can often be defined in pairs. For example, `Customer` may have a relation named `orders` while `Order` may have a relation
+named `customer`:
+
+```php
+class Customer extends ActiveRecord
+{
+	....
+	public function getOrders()
+	{
+		return $this->hasMany(Order::className, ['customer_id' => 'id']);
+	}
+}
+
+class Order extends ActiveRecord
+{
+	....
+	public function getCustomer()
+	{
+		return $this->hasOne(Customer::className, ['id' => 'customer_id']);
+	}
+}
+```
+
+If we perform the following query, we would find that the `customer` of an order is not the same customer object
+that finds those orders, and accessing `customer->orders` will trigger one SQL execution while accessing
+the `customer` of an order will trigger another SQL execution:
+
+```php
+// SELECT * FROM tbl_customer WHERE id=1
+$customer = Customer::find(1);
+// echoes "not equal"
+// SELECT * FROM tbl_order WHERE customer_id=1
+// SELECT * FROM tbl_customer WHERE id=1
+if ($customer->orders[0]->customer === $customer) {
+	echo 'equal';
+} else {
+	echo 'not equal';
+}
+```
+
+To avoid the redundant execution of the last SQL statement, we could declare the inverse relations for the `customer`
+and the `orders` relations by calling the `inverseOf()` method, like the following:
+
+```php
+class Customer extends ActiveRecord
+{
+	....
+	public function getOrders()
+	{
+		return $this->hasMany(Order::className, ['customer_id' => 'id'])->inverseOf('customer');
+	}
+}
+```
+
+Now if we execute the same query as shown above, we would get:
+
+```php
+// SELECT * FROM tbl_customer WHERE id=1
+$customer = Customer::find(1);
+// echoes "equal"
+// SELECT * FROM tbl_order WHERE customer_id=1
+if ($customer->orders[0]->customer === $customer) {
+	echo 'equal';
+} else {
+	echo 'not equal';
+}
+```
+
+In the above, we have shown how to use inverse relations in lazy loading. Inverse relations also apply in
+eager loading:
+
+```php
+// SELECT * FROM tbl_customer
+// SELECT * FROM tbl_order WHERE customer_id IN (1, 2, ...)
+$customers = Customer::find()->with('orders')->all();
+// echoes "equal"
+if ($customers[0]->orders[0]->customer === $customers[0]) {
+	echo 'equal';
+} else {
+	echo 'not equal';
+}
+```
+
+> Note: Inverse relation cannot be defined with a relation that involves pivoting tables.
+> That is, if your relation iso defined with `via()` or `viaTable()`, you cannot call `inverseOf()` further.
+
+
 Joining with Relations
 ----------------------
 

framework/CHANGELOG.md

@@ -115,6 +115,7 @@ Yii Framework 2 Change Log
 - Enh #2387: Added support for fetching data from database in batches (nineinchnick, qiangxue)
 - Enh #2417: Added possibility to set `dataType` for `$.ajax` call in yii.activeForm.js (Borales)
 - Enh #2436: Label of the attribute, which looks like `relatedModel.attribute`, will be received from the related model if it available (djagya)
+- Enh #2415: Added support for inverse relations (qiangxue)
 - Enh: Added support for using arrays as option values for console commands (qiangxue)
 - Enh: Added `favicon.ico` and `robots.txt` to default application templates (samdark)
 - Enh: Added `Widget::autoIdPrefix` to support prefixing automatically generated widget IDs (qiangxue)

framework/db/ActiveRelationTrait.php

@@ -8,6 +8,7 @@
 namespace yii\db;
 
 use yii\base\InvalidConfigException;
+use yii\base\InvalidParamException;
 
 /**
  * ActiveRelationTrait implements the common methods and properties for active record relation classes.
@@ -40,6 +41,15 @@ trait ActiveRelationTrait
 	 * to set this property instead of directly setting it.
 	 */
 	public $via;
+	/**
+	 * @var string the name of the relation that is the inverse of this relation.
+	 * For example, an order has a customer, which means the inverse of the "customer" relation
+	 * is the "orders", and the inverse of the "orders" relation is the "customer".
+	 * If this property is set, the primary record(s) will be referenced through the specified relation.
+	 * For example, `$customer->orders[0]->customer` and `$customer` will be the same object,
+	 * and accessing the customer of an order will not trigger new DB query.
+	 */
+	public $inverseOf;
 
 	/**
 	 * Clones internal objects.
@@ -72,6 +82,67 @@ trait ActiveRelationTrait
 	}
 
 	/**
+	 * Sets the name of the relation that is the inverse of this relation.
+	 * For example, an order has a customer, which means the inverse of the "customer" relation
+	 * is the "orders", and the inverse of the "orders" relation is the "customer".
+	 * If this property is set, the primary record(s) will be referenced through the specified relation.
+	 * For example, `$customer->orders[0]->customer` and `$customer` will be the same object,
+	 * and accessing the customer of an order will not trigger new DB query.
+	 * @param string $relationName the name of the relation that is the inverse of this relation.
+	 * @return static the relation object itself.
+	 */
+	public function inverseOf($relationName)
+	{
+		$this->inverseOf = $relationName;
+		return $this;
+	}
+
+	/**
+	 * Finds the related records for the specified primary record.
+	 * This method is invoked when a relation of an ActiveRecord is being accessed in a lazy fashion.
+	 * @param string $name the relation name
+	 * @param ActiveRecordInterface $model the primary model
+	 * @return mixed the related record(s)
+	 * @throws InvalidParamException if the relation is invalid
+	 */
+	public function findFor($name, $model)
+	{
+		if (method_exists($model, 'get' . $name)) {
+			$method = new \ReflectionMethod($model, 'get' . $name);
+			$realName = lcfirst(substr($method->getName(), 3));
+			if ($realName !== $name) {
+				throw new InvalidParamException('Relation names are case sensitive. ' . get_class($model) . " has a relation named \"$realName\" instead of \"$name\".");
+			}
+		}
+
+		$related = $this->multiple ? $this->all() : $this->one();
+
+		if ($this->inverseOf === null || empty($related)) {
+			return $related;
+		}
+
+		$inverseRelation = (new $this->modelClass)->getRelation($this->inverseOf);
+
+		if ($this->multiple) {
+			foreach ($related as $i => $relatedModel) {
+				if ($relatedModel instanceof ActiveRecordInterface) {
+					$relatedModel->populateRelation($this->inverseOf, $inverseRelation->multiple ? [$model] : $model);
+				} else {
+					$related[$i][$this->inverseOf] = $inverseRelation->multiple ? [$model] : $model;
+				}
+			}
+		} else {
+			if ($related instanceof ActiveRecordInterface) {
+				$related->populateRelation($this->inverseOf, $inverseRelation->multiple ? [$model] : $model);
+			} else {
+				$related[$this->inverseOf] = $inverseRelation->multiple ? [$model] : $model;
+			}
+		}
+
+		return $related;
+	}
+
+	/**
 	 * Finds the related records and populates them into the primary models.
 	 * @param string $name the relation name
 	 * @param array $primaryModels primary models
@@ -109,6 +180,9 @@ trait ActiveRelationTrait
 				} else {
 					$primaryModels[$i][$name] = $model;
 				}
+				if ($this->inverseOf !== null) {
+					$this->populateInverseRelation($primaryModels, [$model], $name, $this->inverseOf);
+				}
 			}
 			return [$model];
 		} else {
@@ -129,18 +203,73 @@ trait ActiveRelationTrait
 					$primaryModels[$i][$name] = $value;
 				}
 			}
+			if ($this->inverseOf !== null) {
+				$this->populateInverseRelation($primaryModels, $models, $name, $this->inverseOf);
+			}
 			return $models;
 		}
 	}
 
+	private function populateInverseRelation(&$primaryModels, $models, $primaryName, $name)
+	{
+		if (empty($models) || empty($primaryModels)) {
+			return;
+		}
+		$model = reset($models);
+		$relation = $model instanceof ActiveRecordInterface ? $model->getRelation($name) : (new $this->modelClass)->getRelation($name);
+
+		if ($relation->multiple) {
+			$buckets = $this->buildBuckets($primaryModels, $relation->link, null, null, false);
+			if ($model instanceof ActiveRecordInterface) {
+				foreach ($models as $model) {
+					$key = $this->getModelKey($model, $relation->link);
+					$model->populateRelation($name, isset($buckets[$key]) ? $buckets[$key] : []);
+				}
+			} else {
+				foreach ($primaryModels as $i => $primaryModel) {
+					if ($this->multiple) {
+						foreach ($primaryModel as $j => $m) {
+							$key = $this->getModelKey($m, $relation->link);
+							$primaryModels[$i][$j][$name] = isset($buckets[$key]) ? $buckets[$key] : [];
+						}
+					} elseif (!empty($primaryModel[$primaryName])) {
+						$key = $this->getModelKey($primaryModel[$primaryName], $relation->link);
+						$primaryModels[$i][$primaryName][$name] = isset($buckets[$key]) ? $buckets[$key] : [];
+					}
+				}
+			}
+		} else {
+			if ($this->multiple) {
+				foreach ($primaryModels as $i => $primaryModel) {
+					foreach ($primaryModel[$primaryName] as $j => $m) {
+						if ($m instanceof ActiveRecordInterface) {
+							$m->populateRelation($name, $primaryModel);
+						} else {
+							$primaryModels[$i][$primaryName][$j][$name] = $primaryModel;
+						}
+					}
+				}
+			} else {
+				foreach ($primaryModels as $i => $primaryModel) {
+					if ($primaryModels[$i][$primaryName] instanceof ActiveRecordInterface) {
+						$primaryModels[$i][$primaryName]->populateRelation($name, $primaryModel);
+					} elseif  (!empty($primaryModels[$i][$primaryName])) {
+						$primaryModels[$i][$primaryName][$name] = $primaryModel;
+					}
+				}
+			}
+		}
+	}
+
 	/**
 	 * @param array $models
 	 * @param array $link
 	 * @param array $viaModels
 	 * @param array $viaLink
+	 * @param boolean $checkMultiple
 	 * @return array
 	 */
-	private function buildBuckets($models, $link, $viaModels = null, $viaLink = null)
+	private function buildBuckets($models, $link, $viaModels = null, $viaLink = null, $checkMultiple = true)
 	{
 		if ($viaModels !== null) {
 			$map = [];
@@ -180,7 +309,7 @@ trait ActiveRelationTrait
 			}
 		}
 
-		if (!$this->multiple) {
+		if ($checkMultiple && !$this->multiple) {
 			foreach ($buckets as $i => $bucket) {
 				$buckets[$i] = reset($bucket);
 			}

framework/db/BaseActiveRecord.php

@@ -231,17 +231,10 @@ abstract class BaseActiveRecord extends Model implements ActiveRecordInterface
 			}
 			$value = parent::__get($name);
 			if ($value instanceof ActiveRelationInterface) {
-				if (method_exists($this, 'get' . $name)) {
-					$method = new \ReflectionMethod($this, 'get' . $name);
-					$realName = lcfirst(substr($method->getName(), 3));
-					if ($realName !== $name) {
-						throw new InvalidParamException('Relation names are case sensitive. ' . get_class($this) . " has a relation named \"$realName\" instead of \"$name\".");
-					}
-				}
-				$this->populateRelation($name, $value->multiple ? $value->all() : $value->one());
-				return $this->_related[$name];
+				return $this->_related[$name] = $value->findFor($name, $this);
+			} else {
+				return $value;
 			}
-			return $value;
 		}
 	}
 

tests/unit/data/ar/Customer.php

@@ -29,6 +29,11 @@ class Customer extends ActiveRecord
 		return $this->hasMany(Order::className(), ['customer_id' => 'id'])->orderBy('id');
 	}
 
+	public function getOrders2()
+	{
+		return $this->hasMany(Order::className(), ['customer_id' => 'id'])->inverseOf('customer2')->orderBy('id');
+	}
+
 	public function afterSave($insert)
 	{
 		ActiveRecordTest::$afterSaveInsert = $insert;

tests/unit/data/ar/Order.php

@@ -22,6 +22,11 @@ class Order extends ActiveRecord
 		return $this->hasOne(Customer::className(), ['id' => 'customer_id']);
 	}
 
+	public function getCustomer2()
+	{
+		return $this->hasOne(Customer::className(), ['id' => 'customer_id'])->inverseOf('orders2');
+	}
+
 	public function getOrderItems()
 	{
 		return $this->hasMany(OrderItem::className(), ['order_id' => 'id']);

tests/unit/framework/db/ActiveRecordTest.php

@@ -324,4 +324,57 @@ class ActiveRecordTest extends DatabaseTestCase
 		$this->assertEquals(0, count($orders[1]->books2));
 		$this->assertEquals(1, count($orders[2]->books2));
 	}
+
+	public function testInverseOf()
+	{
+		// eager loading: find one and all
+		$customer = Customer::find()->with('orders2')->where(['id' => 1])->one();
+		$this->assertTrue($customer->orders2[0]->customer2 === $customer);
+		$customers = Customer::find()->with('orders2')->where(['id' => [1, 3]])->all();
+		$this->assertTrue($customers[0]->orders2[0]->customer2 === $customers[0]);
+		$this->assertTrue(empty($customers[1]->orders2));
+		// lazy loading
+		$customer = Customer::find(2);
+		$orders = $customer->orders2;
+		$this->assertTrue(count($orders) === 2);
+		$this->assertTrue($customer->orders2[0]->customer2 === $customer);
+		$this->assertTrue($customer->orders2[1]->customer2 === $customer);
+		// ad-hoc lazy loading
+		$customer = Customer::find(2);
+		$orders = $customer->getOrders2()->all();
+		$this->assertTrue(count($orders) === 2);
+		$this->assertTrue($customer->orders2[0]->customer2 === $customer);
+		$this->assertTrue($customer->orders2[1]->customer2 === $customer);
+
+		// the other way around
+		$customer = Customer::find()->with('orders2')->where(['id' => 1])->asArray()->one();
+		$this->assertTrue($customer['orders2'][0]['customer2']['id'] === $customer['id']);
+		$customers = Customer::find()->with('orders2')->where(['id' => [1, 3]])->asArray()->all();
+		$this->assertTrue($customer['orders2'][0]['customer2']['id'] === $customers[0]['id']);
+		$this->assertTrue(empty($customers[1]['orders2']));
+
+		$orders = Order::find()->with('customer2')->where(['id' => 1])->all();
+		$this->assertTrue($orders[0]->customer2->orders2 === [$orders[0]]);
+		$order = Order::find()->with('customer2')->where(['id' => 1])->one();
+		$this->assertTrue($order->customer2->orders2 === [$order]);
+
+		$orders = Order::find()->with('customer2')->where(['id' => 1])->asArray()->all();
+		$this->assertTrue($orders[0]['customer2']['orders2'][0]['id'] === $orders[0]['id']);
+		$order = Order::find()->with('customer2')->where(['id' => 1])->asArray()->one();
+		$this->assertTrue($order['customer2']['orders2'][0]['id'] === $orders[0]['id']);
+
+		$orders = Order::find()->with('customer2')->where(['id' => [1, 3]])->all();
+		$this->assertTrue($orders[0]->customer2->orders2 === [$orders[0]]);
+		$this->assertTrue($orders[1]->customer2->orders2 === [$orders[1]]);
+
+		$orders = Order::find()->with('customer2')->where(['id' => [2, 3]])->orderBy('id')->all();
+		$this->assertTrue($orders[0]->customer2->orders2 === $orders);
+		$this->assertTrue($orders[1]->customer2->orders2 === $orders);
+
+		$orders = Order::find()->with('customer2')->where(['id' => [2, 3]])->orderBy('id')->asArray()->all();
+		$this->assertTrue($orders[0]['customer2']['orders2'][0]['id'] === $orders[0]['id']);
+		$this->assertTrue($orders[0]['customer2']['orders2'][1]['id'] === $orders[1]['id']);
+		$this->assertTrue($orders[1]['customer2']['orders2'][0]['id'] === $orders[0]['id']);
+		$this->assertTrue($orders[1]['customer2']['orders2'][1]['id'] === $orders[1]['id']);
+	}
 }