Reference types using @id instead of duplicating type

generator/templates/static/BaseType.php

@@ -61,6 +61,14 @@ public function getProperties(): array
         return $this->properties;
     }
 
+    /**
+     * @return ReferencedType|static
+     */
+    public function referenced()
+    {
+        return new ReferencedType($this);
+    }
+
     public function offsetExists($offset)
     {
         return array_key_exists($offset, $this->properties);

generator/templates/static/ReferencedType.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Spatie\SchemaOrg;
+
+use JsonSerializable;
+
+class ReferencedType implements Type, JsonSerializable
+{
+    /** @var Type */
+    protected $type;
+
+    public function __construct(Type $type)
+    {
+        $this->type = $type;
+    }
+
+    public function toArray(): array
+    {
+        return [
+            '@id' => $this->type->toArray()['@id'] ?? null,
+        ];
+    }
+
+    public function toScript(): string
+    {
+        return $this->type->toScript();
+    }
+
+    public function jsonSerialize()
+    {
+        return $this->toArray();
+    }
+
+    public function __toString(): string
+    {
+        return $this->toScript();
+    }
+}

src/BaseType.php

@@ -61,6 +61,14 @@ public function getProperties(): array
         return $this->properties;
     }
 
+    /**
+     * @return ReferencedType|static
+     */
+    public function referenced()
+    {
+        return new ReferencedType($this);
+    }
+
     public function offsetExists($offset)
     {
         return array_key_exists($offset, $this->properties);

src/ReferencedType.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Spatie\SchemaOrg;
+
+use JsonSerializable;
+
+class ReferencedType implements Type, JsonSerializable
+{
+    /** @var Type */
+    protected $type;
+
+    public function __construct(Type $type)
+    {
+        $this->type = $type;
+    }
+
+    public function toArray(): array
+    {
+        return [
+            '@id' => $this->type->toArray()['@id'] ?? null,
+        ];
+    }
+
+    public function toScript(): string
+    {
+        return $this->type->toScript();
+    }
+
+    public function jsonSerialize()
+    {
+        return $this->toArray();
+    }
+
+    public function __toString(): string
+    {
+        return $this->toScript();
+    }
+}

tests/BaseTypeTest.php

@@ -324,6 +324,29 @@ public function it_replaces_identifier_with_at_id_property()
 
         $this->assertEquals($expected, $type->toArray());
     }
+
+    /** @test */
+    public function it_can_reference_type_by_identifier()
+    {
+        $type1 = new AnotherDummyType();
+        $type1->setProperty('identifier', '#1');
+        $type1->setProperty('name', 'another-object');
+        $type2 = new DummyType();
+        $type2->setProperty('identifier', '#2');
+        $type1->setProperty('name', 'object');
+        $type2->setProperty('referenced', $type1->referenced());
+
+        $expected = [
+            '@context' => 'https://schema.org',
+            '@type' => 'DummyType',
+            '@id' => '#2',
+            'referenced' => [
+                '@id' => '#1',
+            ],
+        ];
+
+        $this->assertEquals($expected, $type2->toArray());
+    }
 }
 
 class DummyType extends BaseType

tests/GraphTest.php

@@ -210,4 +210,24 @@ public function it_can_do_things_conditionally()
         $this->assertEquals('spatie', $graph->organization()['name']);
         $this->assertNotEquals('organization', $graph->organization()['name']);
     }
+
+    /** @test */
+    public function it_can_use_references()
+    {
+        $graph = new Graph();
+
+        $graph->blogPosting()
+            ->identifier('https://example.com/blog/my-post/#blogPosting')
+            ->author($graph->organization()->name('organization')->referenced())
+            ->publisher($graph->organization()->url('https://example.com')->referenced());
+
+        $graph->organization()
+            ->identifier('https://example.com/#organization')
+            ->email('[email protected]');
+
+        $this->assertEquals(
+            '<script type="application/ld+json">{"@context":"https:\/\/schema.org","@graph":[{"@type":"BlogPosting","author":{"@id":"https:\/\/example.com\/#organization"},"publisher":{"@id":"https:\/\/example.com\/#organization"},"@id":"https:\/\/example.com\/blog\/my-post\/#blogPosting"},{"@type":"Organization","name":"organization","url":"https:\/\/example.com","email":"[email protected]","@id":"https:\/\/example.com\/#organization"}]}</script>',
+            $graph->toScript()
+        );
+    }
 }