diff --git a/php-wp-unit.xml b/php-wp-unit.xml
index d9c07e2..71fd3e2 100644
--- a/php-wp-unit.xml
+++ b/php-wp-unit.xml
@@ -1,13 +1,12 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 	bootstrap="tests/wp_bootstrap.php"
-	backupGlobals="false"
 	colors="true"
 	convertErrorsToExceptions="true"
-	convertNoticesToExceptions="true"
-	convertWarningsToExceptions="true"
-	verbose="true"
-	>
+	convertNoticesToExceptions="false"
+	convertWarningsToExceptions="false"
+	beStrictAboutTestsThatDoNotTestAnything="false"
+	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
 	<php>
 		<const name="DOING_TESTS" value="1" />
 		<const name="CLIENT_NAME" value="client-test" />
diff --git a/phpunit.xml b/phpunit.xml
index 837590c..169ea16 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,12 +1,12 @@
 <?xml version="1.0"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         bootstrap="tests/bootstrap.php"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         beStrictAboutTestsThatDoNotTestAnything="false"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+    bootstrap="tests/bootstrap.php"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    beStrictAboutTestsThatDoNotTestAnything="false"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
     <coverage includeUncoveredFiles="true">
         <include>
             <directory suffix=".php">./src</directory>
diff --git a/src/Abstracts/Connection.php b/src/Abstracts/Connection.php
index a381ad4..0f9e6a5 100644
--- a/src/Abstracts/Connection.php
+++ b/src/Abstracts/Connection.php
@@ -7,7 +7,7 @@
 class Connection implements IArrayConvertable
 {
     public ?int $id = 0;
-    protected ?string $title;
+    public ?string $title;
     public string $relation = '';
     public int $from;
     public int $to;
diff --git a/src/Abstracts/IQuery.php b/src/Abstracts/IQuery.php
deleted file mode 100644
index a61114e..0000000
--- a/src/Abstracts/IQuery.php
+++ /dev/null
@@ -1,14 +0,0 @@
-<?php
-
-namespace iTRON\wpConnections\Abstracts;
-
-interface IQuery extends IGetSet
-{
-    /**
-     * TRUE means PATCH-like updating, FALSE means PUT-like updating.
-     *
-     * @return bool
-     */
-    public function isUpdate(): bool;
-    public function setIsUpdate(bool $isUpdate);
-}
diff --git a/src/Abstracts/Storage.php b/src/Abstracts/Storage.php
index 61e41b2..6189c60 100644
--- a/src/Abstracts/Storage.php
+++ b/src/Abstracts/Storage.php
@@ -2,15 +2,15 @@
 
 namespace iTRON\wpConnections\Abstracts;
 
+use iTRON\wpConnections\MetaCollection;
 use iTRON\wpConnections\Query;
 use iTRON\wpConnections\ConnectionCollection;
 use iTRON\wpConnections\Exceptions\ConnectionWrongData;
-use iTRON\wpConnections\Query\Connection;
 
 abstract class Storage
 {
     /**
-     * @param Connection $connectionQuery
+     * @param Query\Connection $connectionQuery
      * @throws ConnectionWrongData
      *
      * @return int Connection ID
@@ -18,12 +18,9 @@ abstract class Storage
     abstract public function createConnection(Query\Connection $connectionQuery): int;
 
     /**
-     * @param Query\Connection $connectionQuery
      * @return bool Successful or not.
-     *
-     * @throws ConnectionWrongData
      */
-    abstract public function updateConnection(Query\Connection $connectionQuery): bool;
+    abstract public function updateConnection(Connection $connection): bool;
 
     /**
      * Deletes connections by set of connection IDs.
@@ -64,11 +61,12 @@ abstract public function findConnections(Query\Connection $params): ConnectionCo
      * Only adds meta fields to the DB.
      *
      * @param int $objectID
-     * @param Query\MetaCollection $metaQuery
+     * @param Query\MetaCollection $metaCollection
+     *
      * @return void
      * @throws ConnectionWrongData
      */
-    abstract public function addConnectionMeta(int $objectID, Query\MetaCollection $metaQuery);
+    abstract public function addConnectionMeta(int $objectID, MetaCollection $metaCollection): void;
 
     /**
      * @throws ConnectionWrongData
diff --git a/src/ClientRestApi.php b/src/ClientRestApi.php
index 9195345..1618319 100644
--- a/src/ClientRestApi.php
+++ b/src/ClientRestApi.php
@@ -7,6 +7,7 @@
 use iTRON\wpConnections\Exceptions\ClientRegisterFail;
 use iTRON\wpConnections\Exceptions\ConnectionNotFound;
 use iTRON\wpConnections\Exceptions\Exception;
+use iTRON\wpConnections\Exceptions\RelationNotFound;
 use iTRON\wpConnections\RestResponse\CollectionItem;
 use Ramsey\Collection\Exception\OutOfBoundsException;
 use WP_Error;
@@ -100,31 +101,39 @@ public function restUpdateConnection(WP_REST_Request $request)
      */
     public function restUpdateConnectionMeta(WP_REST_Request $request)
     {
-        $queryConnection = new Query\Connection();
-        $queryConnection->set('id', $request->get_param('connectionID'));
+        try {
+            $queryConnection = new Query\Connection();
+            $queryConnection->id = $request->get_param('connectionID');
 
-        if ('PUT' === $request->get_method()) {
-            $queryConnection->meta->setIsUpdate(false);
-        }
+            $found = $this->getClient()->getRelation($request->get_param('relation'))->findConnections($queryConnection);
 
-        $queryConnection->meta->fromArray((array) $request->get_param('meta'));
+            if ($found->isEmpty()) {
+                return rest_ensure_response($this->getError(new ConnectionNotFound()));
+            }
 
-        if ('PATCH' === $request->get_method()) {
-            $queryConnection->meta->map(
-                function ($item) {
-                    /** @var Query\Connection $item */
-                    $item->setIsUpdate(false);
-                }
-            );
-        }
+            $connection = $found->first();
 
-        try {
-            $result = $this->getClient()->getRelation($request->get_param('relation'))->updateConnectionMeta($queryConnection);
+            if ('PUT' === $request->get_method()) {
+                $connection->meta->clear();
+            }
+
+            if ('PATCH' === $request->get_method()) {
+                $filtered_meta = $connection->meta->filter(function (Meta $meta) use ($request) {
+                    return ! in_array($meta->getKey(), array_column($request->get_param('meta'), 'key'));
+                });
+
+                $connection->meta->clear();
+                $connection->meta->fromArray($filtered_meta->toArray());
+            }
+
+            $connection->meta->fromArray((array) $request->get_param('meta'));
+
+            $connection->update();
         } catch (Exception $e) {
             return rest_ensure_response($this->getError($e));
         }
 
-        return [ 'updated' => $result ];
+        return rest_ensure_response([ 'updated' => $connection ]);
     }
 
     public function restDeleteConnectionMeta(WP_REST_Request $request)
diff --git a/src/Connection.php b/src/Connection.php
index 2170a7c..ae15e51 100644
--- a/src/Connection.php
+++ b/src/Connection.php
@@ -2,6 +2,8 @@
 
 namespace iTRON\wpConnections;
 
+use iTRON\wpConnections\Exceptions\ConnectionWrongData;
+
 class Connection extends Abstracts\Connection
 {
     use ClientInterface;
@@ -19,10 +21,22 @@ public function __clone()
     }
 
     /**
-     * Saves instance to DB
+     * Saves instance to DB.
+     * Cannot be used to create new instance, only to update existing.
+     * This method overrides fields in a storage, not appends, and deletes all meta fields in a storage before saving.
+     *
+     * @throws ConnectionWrongData
      */
-    public function save()
+    public function update(): void
     {
+        if (empty($this->id)) {
+            throw new ConnectionWrongData('Cannot update uninitialized connection', 304);
+        }
+
+        $this->getClient()->getStorage()->updateConnection($this);
+
+        $this->getClient()->getStorage()->removeConnectionMeta($this->id, new Query\MetaCollection());
+        $this->getClient()->getStorage()->addConnectionMeta($this->id, $this->meta);
     }
 
     /**
@@ -39,8 +53,12 @@ protected function loadFromQuery(Query\Connection $connectionQuery): Connection
         $this->relation = $connectionQuery->get('relation');
         $this->from = $connectionQuery->get('from');
         $this->to = $connectionQuery->get('to');
-        $this->meta = clone $connectionQuery->get('meta');
+        $this->meta = new MetaCollection();
+        $this->meta->fromArray($connectionQuery->get('meta')->toArray());
         $this->order = $connectionQuery->get('order');
+        if ($connectionQuery->get('client')) {
+            $this->setClient($connectionQuery->get('client'));
+        }
 
         return $this;
     }
diff --git a/src/ConnectionCollection.php b/src/ConnectionCollection.php
index 185e9dd..37dffd9 100644
--- a/src/ConnectionCollection.php
+++ b/src/ConnectionCollection.php
@@ -46,16 +46,13 @@ private function fromArray(array $items, string $collectionType = ''): array
             if (! isset($item->to)) {
                 continue;
             }
-            if (! isset($item->order)) {
-                continue;
-            }
 
             $connectionQuery = new Query\Connection();
             $connectionQuery
                 ->set('id', $item->ID)
                 ->set('from', $item->from)
                 ->set('to', $item->to)
-                ->set('order', $item->order)
+                ->set('order', $item->order ?? 0)
                 ->set('title', $item->title ?? '')
                 ->set('client', $item->client ?? null)
                 ->set('relation', $item->relation ?? null);
diff --git a/src/IQueryTrait.php b/src/IQueryTrait.php
deleted file mode 100644
index 4c9dcec..0000000
--- a/src/IQueryTrait.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace iTRON\wpConnections;
-
-trait IQueryTrait
-{
-    protected bool $isUpdate = true;
-
-    public function isUpdate(): bool
-    {
-        return $this->isUpdate;
-    }
-
-    public function setIsUpdate(bool $isUpdate)
-    {
-        $this->isUpdate = $isUpdate;
-    }
-}
diff --git a/src/Query/Connection.php b/src/Query/Connection.php
index baa6579..46a086a 100644
--- a/src/Query/Connection.php
+++ b/src/Query/Connection.php
@@ -2,14 +2,11 @@
 
 namespace iTRON\wpConnections\Query;
 
-use iTRON\wpConnections\Abstracts\IQuery;
 use iTRON\wpConnections\GSInterface;
-use iTRON\wpConnections\IQueryTrait;
 
-class Connection extends \iTRON\wpConnections\Abstracts\Connection implements IQuery
+class Connection extends \iTRON\wpConnections\Abstracts\Connection
 {
     use GSInterface;
-    use IQueryTrait;
 
     public int $both = 0;
 
diff --git a/src/Query/MetaCollection.php b/src/Query/MetaCollection.php
index 5ea20c8..2cee2d0 100644
--- a/src/Query/MetaCollection.php
+++ b/src/Query/MetaCollection.php
@@ -2,13 +2,10 @@
 
 namespace iTRON\wpConnections\Query;
 
-use iTRON\wpConnections\Abstracts\IQuery;
 use iTRON\wpConnections\GSInterface;
-use iTRON\wpConnections\IQueryTrait;
 
-class MetaCollection extends \iTRON\wpConnections\MetaCollection implements IQuery
+class MetaCollection extends \iTRON\wpConnections\MetaCollection
 {
-    use IQueryTrait;
     use GSInterface;
 
     public string $collectionType = Meta::class;
diff --git a/src/Relation.php b/src/Relation.php
index 0e2c59b..6485ff6 100644
--- a/src/Relation.php
+++ b/src/Relation.php
@@ -88,52 +88,20 @@ public function createConnection(Query\Connection $connectionQuery): Connection
 
         $this->getClient()->getStorage()->createConnection($connectionQuery);
 
-        return new Connection($connectionQuery);
+        $connection = new Connection($connectionQuery);
+        $connection->setClient($this->getClient());
+
+        do_action('wpConnections/relation/created', $connection);
+
+        return $connection;
     }
 
-    /**
-     * @throws ConnectionWrongData
-     */
     public function updateConnection(Query\Connection $connectionQuery): bool
     {
         $connectionQuery->set('relation', $this->name);
         return $this->getClient()->getStorage()->updateConnection($connectionQuery);
     }
 
-    /**
-     * @throws ConnectionWrongData
-     */
-    public function updateConnectionMeta(Query\Connection $connectionQuery): bool
-    {
-        $connectionQuery->set('relation', $this->name);
-        $objectID = $connectionQuery->get('id');
-
-        /** @var Query\MetaCollection $metaQuery */
-        $metaQuery = $connectionQuery->get('meta');
-
-        if (! $metaQuery->isUpdate()) {
-            // Remove all meta fields first if false === isUpdate.
-            $this->getClient()->getStorage()->removeConnectionMeta($objectID, new Query\MetaCollection());
-        } else {
-            // Check the array items for false === $isUpdate fields in order to remove older values.
-            $toRemove = $metaQuery->where('isUpdate', false);
-            if (! $toRemove->isEmpty()) {
-                foreach ($toRemove->getIterator() as $meta) {
-                    /** @var Meta $meta */
-                    $meta->setValue(null);
-                }
-                $this->getClient()->getStorage()->removeConnectionMeta($objectID, $toRemove);
-            }
-        }
-
-        // Finally, insert new meta fields.
-        if (! $metaQuery->isEmpty()) {
-            $this->getClient()->getStorage()->addConnectionMeta($objectID, $metaQuery);
-        }
-
-        return true;
-    }
-
     /**
      * @throws ConnectionWrongData
      */
diff --git a/src/Settings.php b/src/Settings.php
index 0ecc811..df8ec21 100644
--- a/src/Settings.php
+++ b/src/Settings.php
@@ -22,7 +22,7 @@ protected function setLogging()
         };
 
         add_action('wpConnections/storage/findConnections/dbQuery', $f, 10, 2);
-        add_action('wpConnections/storage/removeConnectionMeta/dbQuery', $f, 10, 2);
+        add_action('wpConnections/storage/removeConnectionMeta/after', $f, 10, 5);
         add_action('wpConnections/storage/deletedSpecificConnections', $f, 10, 3);
     }
 }
diff --git a/src/WPStorage.php b/src/WPStorage.php
index 8d64168..6daafa7 100644
--- a/src/WPStorage.php
+++ b/src/WPStorage.php
@@ -4,7 +4,6 @@
 
 use iTRON\wpConnections\Exceptions\ConnectionWrongData;
 use iTRON\wpConnections\Helpers\Database;
-use iTRON\wpConnections\Query\MetaCollection;
 
 class WPStorage extends Abstracts\Storage
 {
@@ -327,7 +326,11 @@ public function findConnections(Query\Connection $params): ConnectionCollection
             $data[ $connection->ID ] = $item;
         }
 
-        return new ConnectionCollection($data);
+        $collection = new ConnectionCollection($data);
+
+        do_action('wpConnections/storage/findConnections/dbQuery/data', $query, $query_result, $data, $collection->toArray());
+
+        return $collection;
     }
 
     /**
@@ -381,61 +384,36 @@ public function createConnection(Query\Connection $connectionQuery): int
         return $connection_id;
     }
 
-    public function updateConnection(Query\Connection $connectionQuery): bool
+    public function updateConnection(Abstracts\Connection $connection): bool
     {
         global $wpdb;
 
-        $objectID = $connectionQuery->get('id');
-        if (! is_numeric($objectID)) {
-            throw new Exceptions\ConnectionWrongData("Object ID is undefined.");
-        }
-
-        $where = ['ID' => $objectID];
-        $update = [];
-
-        if (! is_null($title = $connectionQuery->get('title'))) {
-            $update['title'] = $title;
-        }
-
-        if (! empty($from = $connectionQuery->get('from'))) {
-            $update['from'] = $from;
-        }
-
-        if (! empty($to = $connectionQuery->get('to'))) {
-            $update['to'] = $to;
-        }
-
-        if (! is_null($order = $connectionQuery->get('order'))) {
-            $update['order'] = $order;
-        }
-
-        if (! $connectionQuery->isUpdate()) {
-            $update = $connectionQuery->toArray();
-
-            unset($update['meta']);
-            unset($update['relation']);
-        }
-
-        if (! empty($update)) {
-            $updated = $wpdb->update($wpdb->prefix . $this->get_connections_table(), $update, $where);
-        }
+        $where = ['ID' => $connection->id];
+        $update = [
+            'from'      => $connection->from,
+            'to'        => $connection->to,
+            'order'     => $connection->order,
+            'relation'  => $connection->relation,
+            'title'     => $connection->title,
+        ];
 
-        return true;
+        return $wpdb->update($wpdb->prefix . $this->get_connections_table(), $update, $where);
     }
 
     /**
      * Only adds meta fields to the DB.
      *
      * @param int $objectID
-     * @param MetaCollection $metaQuery
+     * @param MetaCollection $metaCollection
+     *
      * @return void
      * @throws ConnectionWrongData
      */
-    public function addConnectionMeta(int $objectID, Query\MetaCollection $metaQuery)
+    public function addConnectionMeta(int $objectID, MetaCollection $metaCollection): void
     {
         global $wpdb;
 
-        if ($metaQuery->isEmpty()) {
+        if ($metaCollection->isEmpty()) {
             throw new Exceptions\ConnectionWrongData("Meta object is empty.");
         }
 
@@ -443,8 +421,10 @@ public function addConnectionMeta(int $objectID, Query\MetaCollection $metaQuery
             throw new Exceptions\ConnectionWrongData("Object ID is empty.");
         }
 
+        do_action('wpConnections/storage/addConnectionMeta/before', $this->getClient(), $objectID, $metaCollection);
+
         $errors = [];
-        foreach ($metaQuery->getIterator() as $meta) {
+        foreach ($metaCollection->getIterator() as $meta) {
             /** @var Query\Meta $meta */
             $data = [
                 'connection_id' => $objectID,
@@ -452,14 +432,14 @@ public function addConnectionMeta(int $objectID, Query\MetaCollection $metaQuery
                 'meta_value'    => $meta->getValue(),
             ];
 
-            do_action('logger', $data);
-
             $result = $wpdb->insert($wpdb->prefix . $this->get_meta_table(), $data);
             if (false === $result) {
                 $errors [] = $wpdb->last_error;
             }
         }
 
+        do_action('wpConnections/storage/addConnectionMeta/after', $this->getClient(), $objectID, $metaCollection, $errors);
+
         if ($errors) {
             $errors = implode('; ', $errors);
             throw new Exceptions\ConnectionWrongData("Database refused inserting new connection meta data with the words: [{$errors}]");
@@ -467,6 +447,10 @@ public function addConnectionMeta(int $objectID, Query\MetaCollection $metaQuery
     }
 
     /**
+     * Deletes meta fields from the DB.
+     * Provide Query\MetaCollection with meta fields to remove.
+     * Put empty Query\MetaCollection to remove all meta fields.
+     *
      * @throws ConnectionWrongData
      */
     public function removeConnectionMeta(int $objectID, Query\MetaCollection $metaQuery)
@@ -501,13 +485,12 @@ public function removeConnectionMeta(int $objectID, Query\MetaCollection $metaQu
         }
 
         $query = $from . implode(' ', $where);
-        $rowsAffected = $wpdb->query($query);
 
-        do_action('wpConnections/storage/removeConnectionMeta/dbQuery', $query, $rowsAffected);
+        do_action('wpConnections/storage/removeConnectionMeta/before', $this->getClient(), $objectID, $metaQuery, $query);
 
-        if (false === $rowsAffected) {
-            throw new Exceptions\ConnectionWrongData("Database refused removing new connection meta data with the words: [{$wpdb->last_error}]");
-        }
+        $rowsAffected = $wpdb->query($query);
+
+        do_action('wpConnections/storage/removeConnectionMeta/after', $this->getClient(), $objectID, $metaQuery, $query, $rowsAffected);
 
         return $rowsAffected;
     }
diff --git a/tests/iTRON/wpConnections/WP/WPUnitTest.php b/tests/iTRON/wpConnections/WP/WPUnitTest.php
index fa1e194..e7b2b24 100644
--- a/tests/iTRON/wpConnections/WP/WPUnitTest.php
+++ b/tests/iTRON/wpConnections/WP/WPUnitTest.php
@@ -3,10 +3,18 @@
 namespace iTRON\wpConnections\Tests\iTRON\wpConnections\WP;
 
 use iTRON\wpConnections\Client;
+use iTRON\wpConnections\ClientRestApi;
+use iTRON\wpConnections\ConnectionCollection;
+use iTRON\wpConnections\Exceptions\ConnectionWrongData;
+use iTRON\wpConnections\Meta;
 use iTRON\wpConnections\Query\Connection;
 use iTRON\wpConnections\Query\Relation;
 use PHPUnit\Framework\TestCase;
 
+use Ramsey\Collection\Exception\OutOfBoundsException;
+
+use function PHPUnit\Framework\assertEquals;
+
 class WPUnitTest extends TestCase
 {
 	protected Client $client;
@@ -71,5 +79,208 @@ public function testCreateConnection()
 		self::assertEquals( $connection_query->id, $connection->id );
 		self::assertEquals( $connection_query->from, $connection->from );
 		self::assertEquals( $connection_query->to, $connection->to );
+
+		return $connection;
+	}
+
+	public function testFindConnections() {
+		// Create new page.
+		$page_id = wp_insert_post( [
+			'post_title' => 'Test Find Connections',
+			'post_content' => 'Page content',
+			'post_status' => 'publish',
+			'post_type' => 'page',
+		] );
+
+		// Create new post.
+		$post_id = wp_insert_post( [
+			'post_title' => 'Test Find Connections',
+			'post_content' => 'Post content',
+			'post_status' => 'publish',
+			'post_type' => 'post',
+		] );
+
+		// Create new connection.
+		$connection_query = new Connection(
+			$page_id,
+			$post_id
+		);
+		$connection_query->title = 'Test Find Connections';
+
+		$connection = $this->client->getRelation( RELATION_NAME )->createConnection( $connection_query );
+
+		// Find the connection by ID.
+		$find_query = new Connection();
+		$find_query->id = $connection->id;
+
+		$found_connections = $this->client->getRelation( RELATION_NAME )->findConnections( $find_query );
+
+		self::assertEquals( 1, $found_connections->count() );
+		self::assertEquals( $connection->id, $found_connections->first()->id );
+	}
+
+	/**
+	 * @depends testCreateConnection
+	 */
+	public function testUpdateConnection( $connection )
+	{
+		$title = 'New test title';
+		$order = 10;
+
+		// Create new page.
+		$page_id = wp_insert_post( [
+			'post_title' => 'Page 2',
+			'post_content' => 'Page 2 content',
+			'post_status' => 'publish',
+			'post_type' => 'page',
+		] );
+
+		// Create new post.
+		$post_id = wp_insert_post( [
+			'post_title' => 'Post 2',
+			'post_content' => 'Post 2 content',
+			'post_status' => 'publish',
+			'post_type' => 'post',
+		] );
+
+		// Find the connection.
+		$connection_query = new Connection(
+			$page_id,
+			$post_id
+		);
+		$connection_query->title = 'Test Update Connection';
+
+		$connection = $this->client->getRelation( RELATION_NAME )->createConnection( $connection_query );
+
+		// Create new post.
+		$post_id = wp_insert_post( [
+			'post_title' => 'Post 3',
+			'post_content' => 'Post 3 content',
+			'post_status' => 'publish',
+			'post_type' => 'post',
+		] );
+
+		$connection->title = $title;
+		$connection->order = $order;
+		$connection->to = $post_id;
+
+		$meta0 = new Meta(
+			'key0',
+			'value0'
+		);
+		$connection->meta->add( $meta0 );
+
+		// Update the connection.
+		$connection->update();
+
+		// Find the connection again.
+		$connection = $this->client->getRelation( RELATION_NAME )->findConnections( $connection_query )->first();
+
+		self::assertEquals( $title, $connection->title );
+		self::assertEquals( $order, $connection->order );
+		self::assertEquals( $page_id, $connection->from );
+		self::assertEquals( $post_id, $connection->to );
+		self::assertEquals( 1, $connection->meta->count() );
+		self::assertEquals( $meta0, $connection->meta->first() );
+
+		$meta1 = new Meta(
+			'key1',
+			'value1'
+		);
+		$connection->meta->clear();
+		$connection->meta->add( $meta1 );
+
+		// Update the connection.
+		$connection->update();
+
+		// Find the connection again.
+		$connection = $this->client->getRelation( RELATION_NAME )->findConnections( $connection_query )->first();
+
+		self::assertEquals( 1, $connection->meta->count() );
+		self::assertEquals( $meta1, $connection->meta->first() );
+
+		// Test throwing exception when updating uninitialized connection.
+		$connection_query = new Connection(
+			$this->page_id,
+			$this->post_id
+		);
+
+		$connection = new \iTRON\wpConnections\Connection( $connection_query );
+
+		$this->expectException( ConnectionWrongData::class );
+		$connection->update();
+	}
+
+	public function testRestUpdateMeta() {
+		// Create new page.
+		$page_id = wp_insert_post( [
+			'post_title' => 'Page for REST API tests',
+			'post_content' => 'Page content',
+			'post_status' => 'publish',
+			'post_type' => 'page',
+		] );
+
+		// Create new post.
+		$post_id = wp_insert_post( [
+			'post_title' => 'Post for REST API tests',
+			'post_content' => 'Post content',
+			'post_status' => 'publish',
+			'post_type' => 'post',
+		] );
+
+		// Find the connection.
+		$connection_query = new Connection(
+			$page_id,
+			$post_id
+		);
+
+		$connection = $this->client->getRelation( RELATION_NAME )->createConnection( $connection_query );
+		$meta00 = new Meta( 'key0', 'value00' );
+		$meta01 = new Meta( 'key0', 'value01' );
+		$connection->meta->add( $meta00 );
+		$connection->meta->add( $meta01 );
+		$connection->update();
+
+		$request = new \WP_REST_Request( 'POST' );
+		$meta1 = new Meta( 'key1', 'value1' );
+		$request->set_param( 'connectionID', $connection->id );
+		$request->set_param( 'meta', [$meta1->toArray()] );
+		$request->set_param( 'relation', RELATION_NAME );
+
+		$restapi = new ClientRestApi( $this->client );
+		$response = $restapi->restUpdateConnectionMeta( $request );
+
+		$connection->meta->add( $meta1 );
+		self::assertEquals( 'WP_REST_Response', get_class( $response ) );
+		self::assertEquals( $connection, $response->get_data()['updated'] );
+
+		$meta02 = new Meta( 'key0', 'value02' );
+		$request = new \WP_REST_Request( 'PATCH' );
+		$request->set_param( 'connectionID', $connection->id );
+		$request->set_param( 'meta', [$meta02->toArray()] );
+		$request->set_param( 'relation', RELATION_NAME );
+
+		$response = $restapi->restUpdateConnectionMeta( $request );
+		$connection->meta->remove( $meta00 );
+		$connection->meta->remove( $meta01 );
+		$connection->meta->add( $meta02 );
+
+		self::assertEquals( 'WP_REST_Response', get_class( $response ) );
+		self::assertEquals( $connection->meta->toArray(), $response->get_data()['updated']->meta->toArray() );
+
+		$meta3 = new Meta( 'key3', 'value3' );
+		$meta4 = new Meta( 'key4', 'value4' );
+		$request = new \WP_REST_Request( 'PUT' );
+		$request->set_param( 'connectionID', $connection->id );
+		$request->set_param( 'meta', [$meta3->toArray(), $meta4->toArray()] );
+		$request->set_param( 'relation', RELATION_NAME );
+
+		$response = $restapi->restUpdateConnectionMeta( $request );
+		$connection->meta->clear();
+		$connection->meta->add( $meta3 );
+		$connection->meta->add( $meta4 );
+
+		self::assertEquals( 'WP_REST_Response', get_class( $response ) );
+		self::assertEquals( $connection->meta->toArray(), $response->get_data()['updated']->meta->toArray() );
 	}
 }
diff --git a/tests/wp_bootstrap.php b/tests/wp_bootstrap.php
index 1c066f5..3bf35d3 100644
--- a/tests/wp_bootstrap.php
+++ b/tests/wp_bootstrap.php
@@ -1,5 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
+const UNIT_TESTS = true;
+
+require_once dirname(__DIR__) . '/vendor/autoload.php';
+
 // Define constants for the IDE. Never fired.
 if ( defined( 'PHPSTORM_META' ) ) {
 	define( 'DOING_TESTS', 1 );