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Vector Search Cookbook

This tutorial demonstrates how to use MongoDB Atlas Vector Search with Doctrine MongoDB ODM. Vector search enables semantic queries over vector embeddings, which are typically generated by an embedding system.

Step 1: Generate Vector Embeddings

Before storing data, you need to generate vector embeddings for your documents. You can use an embedding system such as Symfony AI to convert text or other data into a float[] vector.

Example using Voyage AI and Symfony AI:

use Symfony\AI\Platform\Bridge\Voyage\PlatformFactory;$platform = PlatformFactory::create(getenv('VOYAGE_API_KEY'));$vectors = $platform->invoke('voyage-3', <<<'TEXT'    Once upon a time, there was a country called Japan. It was a beautiful country with a lot of mountains and rivers.    The people of Japan were very kind and hardworking. They loved their country very much and took care of it. The    country was very peaceful and prosperous. The people lived happily ever after.    TEXT)->asVectors();

Step 2: Define the Model

Annotate your document with #[VectorSearchIndex] attribute and define a vector field of type float[]. The number of dimensions must match the embedding vector size (e.g., 1024). The similarity metric can be either cosine, euclidean or dotProduct; they all return the same result because Voyage AI uses normalized vectors to length 1.

use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;use Doctrine\ODM\MongoDB\Mapping\ClassMetadata;use Doctrine\ODM\MongoDB\Types\Type;use Symfony\AI\Platform\Vector\Vector;#[ODM\Document]#[ODM\VectorSearchIndex(    fields: [        [            'type' => 'vector',            'path' => 'voyage3Vector',            'numDimensions' => 1024,            'similarity' => ClassMetadata::VECTOR_SIMILARITY_DOT_PRODUCT,        ],        [            'type' => 'filter',            'path' => 'published',        ],    ],    name: 'default',)]class Guide{    #[ODM\Id]    public ?string $id = null;    #[ODM\Field]    public bool $published = false;    #[ODM\Field]    public ?string $content = null;    /** @var list<float>|null Embedding vector created from $content */    #[ODM\Field(type: Type::COLLECTION)]    public ?array $voyage3Vector = null;    /** @param list<float>|Vector $vector */    public function setVoyage3Vector(array|Vector $vector): void    {        if ($vector instanceof Vector) {            if ($vector->getDimensions() !== 1024) {                throw new InvalidArgumentException('The embedding vector must have 1024 dimensions.');            }            $vector = $vector->getData();        }        if (count($vector) !== 1024) {            throw new InvalidArgumentException('The embedding vector must have 1024 dimensions.');        }        $this->voyage3Vector = $vector;    }}

Step 3: Create the Collection and Insert Documents

Use the SchemaManager to create the collection and insert documents with vector embeddings.

$schemaManager = $dm->getSchemaManager();$schemaManager->createDocumentCollection(Guide::class);

Insert documents:

$doc1 = new Guide();$doc1->published = true;$doc1->content = 'First document';$doc2 = new Guide();$doc2->published = false;$dm->persist($doc1);$dm->persist($doc2);$dm->flush();

The vector values of each document can be set later, typically using an asynchronous process:

$vector1 = $embeddingPlatform->invoke($doc1->content)->asVectors()[0];$doc1->setVoyage3Vector($vector1);$vector2 = $embeddingPlatform->invoke($doc2->content)->asVectors()[0];$doc2->setVoyage3Vector($vector2);$dm->flush();

Step 4: Create the Vector Search Index

When updating documents, the vector search index is asynchronously updated by MongoDB Atlas. You have to wait a few seconds before the changes are reflected in search results.

$schemaManager->createDocumentSearchIndexes(Guide::class);

If the vector search index created after inserting documents, the index is marked as "READY" when all existing documents are indexed. You can wait for the index to be ready using the following code:

$schemaManager->waitForSearchIndexes([Guide::class]);

Step 5: Run a Vector Search Aggregation

Use the aggregation builder to run a vector search query:

$results = $dm->createAggregationBuilder(Guide::class)    ->vectorSearch()        ->index('default')        ->path('voyage3Vector')        ->queryVector($vector)        ->filter($qb->expr()->field('published')->equals(true))        ->numCandidates(10)        ->limit(10)    ->set()        ->field('score')        ->expression(['$meta' => 'vectorSearchScore'])    ->getAggregation()->execute()->toArray();var_dump($results);

Notes

Vector embeddings should be generated using a reliable embedding system
The vector field must be of type float[], int[] or bool[], it must match with the embedding vector type and dimensions.
The #[VectorSearchIndex] annotation configures the index for vector search
Use the aggregation builder's vectorSearch stage to query for similar vectors.
Doctrine ODM 2.13+ is required for vector search support.

Maintained

Unmaintained