diff --git a/src/Model/AbstractModel.php b/src/Model/AbstractModel.php
index dd5021a8..81f197cd 100644
--- a/src/Model/AbstractModel.php
+++ b/src/Model/AbstractModel.php
@@ -29,42 +29,34 @@ abstract class AbstractModel implements ModelInterface
      * model is queried, it will load its referenced
      * models together.
      *
-     * @var array
+     * @var string[]
      */
-    public $with = [];
+    public array $with = [];
 
     /**
      * The $dynamic property tells if the object will accept additional fields
      * that are not specified in the $fillable or $guarded properties.
      * This is useful if you do not have a strict document format or
      * if you want to take full advantage of the "schemaless" nature of MongoDB.
-     *
-     * @var bool
      */
-    protected $dynamic = true;
+    protected bool $dynamic = true;
 
     /**
      * Whether the model should manage the `created_at` and `updated_at`
      * timestamps automatically.
-     *
-     * @var bool
      */
-    protected $timestamps = true;
+    protected bool $timestamps = true;
 
     /**
      * Name of the collection where this kind of Model is going to be saved or
      * retrieved from.
-     *
-     * @var string
      */
-    protected $collection = null;
+    protected ?string $collection = null;
 
     /**
      * @see https://docs.mongodb.com/manual/reference/write-concern/
-     *
-     * @var int
      */
-    protected $writeConcern = 1;
+    protected int $writeConcern = 1;
 
     /**
      * Gets a cursor of this kind of entities that matches the query from the
@@ -93,10 +85,8 @@ public static function all(): CursorInterface
      * @param mixed   $query      mongoDB selection criteria
      * @param array   $projection fields to project in Mongo query
      * @param boolean $useCache   retrieves the first through a CacheableCursor
-     *
-     * @return AbstractModel|null
      */
-    public static function first($query = [], array $projection = [], bool $useCache = false)
+    public static function first(mixed $query = [], array $projection = [], bool $useCache = false): ?static
     {
         return self::getBuilderInstance()->first(new static(), $query, $projection, $useCache);
     }
@@ -110,10 +100,8 @@ public static function first($query = [], array $projection = [], bool $useCache
      * @param boolean $useCache   retrieves the first through a CacheableCursor
      *
      * @throws ModelNotFoundException If no document was found
-     *
-     * @return AbstractModel|null
      */
-    public static function firstOrFail($query = [], array $projection = [], bool $useCache = false)
+    public static function firstOrFail(mixed $query = [], array $projection = [], bool $useCache = false): ?static
     {
         return self::getBuilderInstance()->firstOrFail(new static(), $query, $projection);
     }
@@ -124,10 +112,8 @@ public static function firstOrFail($query = [], array $projection = [], bool $us
      * _if field filled.
      *
      * @param mixed $id document id
-     *
-     * @return AbstractModel|null
      */
-    public static function firstOrNew($id)
+    public static function firstOrNew(mixed $id): ?static
     {
         if (!$model = self::first($id)) {
             $model = new static();
@@ -196,10 +182,8 @@ public function fresh(): self
      * Dynamically retrieve attributes on the model.
      *
      * @param string $key name of the attribute
-     *
-     * @return mixed
      */
-    public function &__get(string $key)
+    public function &__get(string $key): mixed
     {
         return $this->getDocumentAttribute($key);
     }
@@ -210,7 +194,7 @@ public function &__get(string $key)
      * @param string $key   attribute name
      * @param mixed  $value value to be set
      */
-    public function __set(string $key, $value): void
+    public function __set(string $key, mixed $value): void
     {
         $this->setDocumentAttribute($key, $value);
     }
diff --git a/src/Model/AttributesService.php b/src/Model/AttributesService.php
index 6bfb9ee5..3a69bd8e 100644
--- a/src/Model/AttributesService.php
+++ b/src/Model/AttributesService.php
@@ -11,47 +11,45 @@ class AttributesService
      * the attributes specified here will be changed
      * with the setDocumentAttribute method.
      *
-     * @var array
+     * @var string[]
      */
-    protected $fillable = [];
+    protected array $fillable = [];
 
     /**
      * The attributes that are not mass assignable. The opposite
      * to the fillable array;.
      *
-     * @var array
+     * @var string[]
      */
-    protected $guarded = [];
+    protected array $guarded = [];
 
     /**
      * Check if model should mutate attributes checking
      * the existence of a specific method on model
      * class. Default is false.
-     *
-     * @var bool
      */
-    protected $mutable = false;
+    protected bool $mutable = false;
 
     /**
      * Store mutable attribute values to work with `&__get()`.
      *
-     * @var array
+     * @var string[]
      */
-    protected $mutableCache = [];
+    protected array $mutableCache = [];
 
     /**
      * The model's attributes.
      *
-     * @var array
+     * @var string[]
      */
-    private $attributes = [];
+    private array $attributes = [];
 
     /**
      * The model attribute's original state.
      *
-     * @var array
+     * @var array<string,mixed>
      */
-    private $originalAttributes = [];
+    private array $originalAttributes = [];
 
     /**
      * {@inheritdoc}
@@ -68,7 +66,7 @@ public static function fill(
         if ($object instanceof PolymorphableModelInterface) {
             $class = $object->polymorph(array_merge($object->getDocumentAttributes(), $input));
 
-            if ($class !== get_class($object)) {
+            if ($class !== $object::class) {
                 $originalAttributes = $object->getDocumentAttributes();
                 $object = new $class();
 
@@ -92,18 +90,12 @@ public static function fill(
         return $object;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function hasDocumentAttribute(string $key): bool
     {
         return !is_null($this->getDocumentAttribute($key));
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function &getDocumentAttribute(string $key)
+    public function &getDocumentAttribute(string $key): mixed
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'get')) {
             $this->mutableCache[$key] = $this->{$this->buildMutatorMethod($key, 'get')}();
@@ -124,9 +116,6 @@ public function &getDocumentAttribute(string $key)
         return $this->attributes[$key];
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function getDocumentAttributes(): array
     {
         foreach ($this->attributes as $field => $value) {
@@ -138,10 +127,7 @@ public function getDocumentAttributes(): array
         return $this->attributes ?? [];
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function cleanDocumentAttribute(string $key)
+    public function cleanDocumentAttribute(string $key): void
     {
         unset($this->attributes[$key]);
 
@@ -150,10 +136,7 @@ public function cleanDocumentAttribute(string $key)
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function setDocumentAttribute(string $key, $value)
+    public function setDocumentAttribute(string $key, $value): void
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'set')) {
             $value = $this->{$this->buildMutatorMethod($key, 'set')}($value);
@@ -172,29 +155,20 @@ public function setDocumentAttribute(string $key, $value)
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function syncOriginalDocumentAttributes()
+    public function syncOriginalDocumentAttributes(): void
     {
         try {
             $this->originalAttributes = unserialize(serialize($this->getDocumentAttributes()));
-        } catch (Exception $e) {
+        } catch (Exception) {
             $this->originalAttributes = $this->getDocumentAttributes();
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function getOriginalDocumentAttributes(): array
     {
         return $this->originalAttributes;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function toArray(): array
     {
         return $this->getDocumentAttributes();
@@ -206,7 +180,7 @@ public function toArray(): array
      * @param string $key    attribute name
      * @param string $prefix method prefix to be used (get, set)
      */
-    protected function hasMutatorMethod(string $key, $prefix): bool
+    protected function hasMutatorMethod(string $key, string $prefix): bool
     {
         $method = $this->buildMutatorMethod($key, $prefix);
 
diff --git a/src/Model/DocumentEmbedder.php b/src/Model/DocumentEmbedder.php
index 0835f1b5..dd7b0301 100644
--- a/src/Model/DocumentEmbedder.php
+++ b/src/Model/DocumentEmbedder.php
@@ -20,7 +20,7 @@ class DocumentEmbedder
      *
      * @return bool Success
      */
-    public function embed($parent, string $field, &$entity): bool
+    public function embed(mixed $parent, string $field, mixed &$entity): bool
     {
         // In order to update the document if it exists inside the $parent
         $this->unembed($parent, $field, $entity);
@@ -42,7 +42,7 @@ public function embed($parent, string $field, &$entity): bool
      *
      * @return bool Success
      */
-    public function unembed($parent, string $field, &$entity): bool
+    public function unembed(mixed $parent, string $field, mixed &$entity): bool
     {
         $fieldValue = (array) $parent->$field;
         $id = $this->getId($entity);
@@ -63,11 +63,11 @@ public function unembed($parent, string $field, &$entity): bool
      *
      * @param mixed        $parent the object where $entity will be referenced
      * @param string       $field  the field where the _id reference of $entity will be stored
-     * @param object|array $entity the object that is being attached
+     * @param mixed $entity the object that is being attached
      *
      * @return bool Success
      */
-    public function attach($parent, string $field, &$entity): bool
+    public function attach(mixed $parent, string $field, mixed &$entity): bool
     {
         $fieldValue = (array) $parent->$field;
         $newId = $this->getId($entity);
@@ -93,7 +93,7 @@ public function attach($parent, string $field, &$entity): bool
      *
      * @return bool Success
      */
-    public function detach($parent, string $field, &$entity): bool
+    public function detach(mixed $parent, string $field, mixed &$entity): bool
     {
         $fieldValue = (array) $parent->$field;
         $newId = $this->getId($entity);
@@ -115,9 +115,8 @@ public function detach($parent, string $field, &$entity): bool
      *
      * @param mixed $object the object|array that the _id will be retrieved from
      *
-     * @return ObjectId|mixed
      */
-    protected function getId(&$object)
+    protected function getId(mixed &$object): mixed
     {
         if (is_array($object)) {
             if (isset($object['_id']) && $object['_id']) {
diff --git a/src/Model/Exception/ModelNotFoundException.php b/src/Model/Exception/ModelNotFoundException.php
index f51e8282..0dfe873e 100644
--- a/src/Model/Exception/ModelNotFoundException.php
+++ b/src/Model/Exception/ModelNotFoundException.php
@@ -17,19 +17,15 @@ class ModelNotFoundException extends RuntimeException
 
     /**
      * Name of the affected Mongolid model.
-     *
-     * @var string
      */
-    protected $model;
+    protected string $model;
 
     /**
      * Set the affected Mongolid model.
      *
      * @param string $model name of the model
-     *
-     * @return $this
      */
-    public function setModel(string $model)
+    public function setModel(string $model): self
     {
         $this->model = $model;
 
@@ -40,10 +36,8 @@ public function setModel(string $model)
 
     /**
      * Get the affected Mongolid model.
-     *
-     * @return string
      */
-    public function getModel()
+    public function getModel(): string
     {
         return $this->model;
     }
diff --git a/src/Model/HasAttributesInterface.php b/src/Model/HasAttributesInterface.php
index d7bdedda..6411b6a5 100644
--- a/src/Model/HasAttributesInterface.php
+++ b/src/Model/HasAttributesInterface.php
@@ -22,10 +22,8 @@ public function hasDocumentAttribute(string $key): bool;
      * Get an attribute from the model.
      *
      * @param string $key the attribute to be accessed
-     *
-     * @return mixed
      */
-    public function getDocumentAttribute(string $key);
+    public function getDocumentAttribute(string $key): mixed;
 
     /**
      * Get all attributes from the model.
@@ -37,7 +35,7 @@ public function getDocumentAttributes(): array;
      *
      * @param string $key name of the attribute to be unset
      */
-    public function cleanDocumentAttribute(string $key);
+    public function cleanDocumentAttribute(string $key): void;
 
     /**
      * Set a given attribute on the model.
@@ -45,7 +43,7 @@ public function cleanDocumentAttribute(string $key);
      * @param string $key   name of the attribute to be set
      * @param mixed  $value value to be set
      */
-    public function setDocumentAttribute(string $key, $value);
+    public function setDocumentAttribute(string $key, mixed $value): void;
 
     /**
      * Stores original attributes from actual data from attributes
@@ -54,7 +52,7 @@ public function setDocumentAttribute(string $key, $value);
      * Ideally should be called once right after retrieving data from
      * the database.
      */
-    public function syncOriginalDocumentAttributes();
+    public function syncOriginalDocumentAttributes(): void;
 
     /**
      * Retrieve original attributes.
diff --git a/src/Model/HasAttributesTrait.php b/src/Model/HasAttributesTrait.php
index 1b3b0993..4387056b 100644
--- a/src/Model/HasAttributesTrait.php
+++ b/src/Model/HasAttributesTrait.php
@@ -24,47 +24,45 @@ trait HasAttributesTrait
      * the attributes specified here will be changed
      * with the setDocumentAttribute method.
      *
-     * @var array
+     * @var string[]
      */
-    protected $fillable = [];
+    protected array $fillable = [];
 
     /**
      * The attributes that are not mass assignable. The opposite
      * to the fillable array;.
      *
-     * @var array
+     * @var string[]
      */
-    protected $guarded = [];
+    protected array $guarded = [];
 
     /**
      * Check if model should mutate attributes checking
      * the existence of a specific method on model
      * class. Default is false.
-     *
-     * @var bool
      */
-    protected $mutable = false;
+    protected bool $mutable = false;
 
     /**
      * Store mutable attribute values to work with `&__get()`.
      *
-     * @var array
+     * @var string[]
      */
-    protected $mutableCache = [];
+    protected array $mutableCache = [];
 
     /**
      * The model's attributes.
      *
-     * @var array
+     * @var array<string,mixed>
      */
-    private $attributes = [];
+    private array $attributes = [];
 
     /**
      * The model attribute's original state.
      *
-     * @var array
+     * @var array<string,mixed>
      */
-    private $originalAttributes = [];
+    private array $originalAttributes = [];
 
     /**
      * Attributes that are cast to another types when fetched from database.
@@ -86,7 +84,7 @@ public static function fill(
         if ($object instanceof PolymorphableModelInterface) {
             $class = $object->polymorph(array_merge($object->getDocumentAttributes(), $input));
 
-            if ($class !== get_class($object)) {
+            if ($class !== $object::class) {
                 $originalAttributes = $object->getDocumentAttributes();
                 $object = new $class();
 
@@ -121,7 +119,7 @@ public function hasDocumentAttribute(string $key): bool
     /**
      * {@inheritdoc}
      */
-    public function &getDocumentAttribute(string $key)
+    public function &getDocumentAttribute(string $key): mixed
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'get')) {
             $this->mutableCache[$key] = $this->{$this->buildMutatorMethod($key, 'get')}();
@@ -166,7 +164,7 @@ public function getDocumentAttributes(): array
     /**
      * {@inheritdoc}
      */
-    public function cleanDocumentAttribute(string $key)
+    public function cleanDocumentAttribute(string $key): void
     {
         unset($this->attributes[$key]);
 
@@ -178,7 +176,7 @@ public function cleanDocumentAttribute(string $key)
     /**
      * {@inheritdoc}
      */
-    public function setDocumentAttribute(string $key, $value)
+    public function setDocumentAttribute(string $key, mixed $value): void
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'set')) {
             $value = $this->{$this->buildMutatorMethod($key, 'set')}($value);
@@ -205,11 +203,11 @@ public function setDocumentAttribute(string $key, $value)
     /**
      * {@inheritdoc}
      */
-    public function syncOriginalDocumentAttributes()
+    public function syncOriginalDocumentAttributes(): void
     {
         try {
             $this->originalAttributes = unserialize(serialize($this->getDocumentAttributes()));
-        } catch (Exception $e) {
+        } catch (Exception) {
             $this->originalAttributes = $this->getDocumentAttributes();
         }
     }
@@ -236,7 +234,7 @@ public function toArray(): array
      * @param string $key    attribute name
      * @param string $prefix method prefix to be used (get, set)
      */
-    protected function hasMutatorMethod(string $key, $prefix): bool
+    protected function hasMutatorMethod(string $key, string $prefix): bool
     {
         $method = $this->buildMutatorMethod($key, $prefix);
 
diff --git a/src/Model/HasLegacyAttributesTrait.php b/src/Model/HasLegacyAttributesTrait.php
index a4910a7e..f15dcf5b 100644
--- a/src/Model/HasLegacyAttributesTrait.php
+++ b/src/Model/HasLegacyAttributesTrait.php
@@ -18,42 +18,40 @@ trait HasLegacyAttributesTrait
     /**
      * The model's attributes.
      *
-     * @var array
+     * @var array<string,mixed>
      */
-    protected $attributes = [];
+    protected array $attributes = [];
 
     /**
      * The model attribute's original state.
      *
-     * @var array
+     * @var array<string,mixed>
      */
-    protected $original = [];
+    protected array $original = [];
 
     /**
      * Once you put at least one string in this array, only
      * the attributes specified here will be changed
      * with the setAttributes method.
      *
-     * @var array
+     * @var string[]
      */
-    protected $fillable = [];
+    protected array $fillable = [];
 
     /**
      * The attributes that are not mass assignable. The opposite
      * to the fillable array;.
      *
-     * @var array
+     * @var string[]
      */
-    protected $guarded = [];
+    protected array $guarded = [];
 
     /**
      * Check if model should mutate attributes checking
      * the existence of a specific method on model
      * class. Default is false.
-     *
-     * @var bool
      */
-    public $mutable = false;
+    public bool $mutable = false;
 
     /**
      * Attributes that are cast to another types when fetched from database.
@@ -64,10 +62,8 @@ trait HasLegacyAttributesTrait
      * Get an attribute from the model.
      *
      * @param string $key the attribute to be accessed
-     *
-     * @return mixed
      */
-    public function getAttribute(string $key)
+    public function getAttribute(string $key): mixed
     {
         $inAttributes = array_key_exists($key, $this->attributes);
 
@@ -79,17 +75,19 @@ public function getAttribute(string $key)
 
         if ($inAttributes) {
             return $this->attributes[$key];
-        } elseif ('attributes' == $key) {
+        }
+
+        if ('attributes' == $key) {
             return $this->attributes;
         }
+
+        return null;
     }
 
     /**
      * Get all attributes from the model.
-     *
-     * @return mixed
      */
-    public function getAttributes()
+    public function getAttributes(): array
     {
         return $this->attributes;
     }
@@ -122,7 +120,7 @@ public function fill(array $input, bool $force = false): HasAttributesInterface
      *
      * @param string $key name of the attribute to be unset
      */
-    public function cleanAttribute(string $key)
+    public function cleanAttribute(string $key): void
     {
         unset($this->attributes[$key]);
     }
@@ -133,7 +131,7 @@ public function cleanAttribute(string $key)
      * @param string $key   name of the attribute to be set
      * @param mixed  $value value to be set
      */
-    public function setAttribute(string $key, $value)
+    public function setAttribute(string $key, mixed $value): void
     {
         if ($casterName = $this->casts[$key] ?? null) {
             $caster = CastResolver::resolve($casterName);
@@ -146,7 +144,7 @@ public function setAttribute(string $key, $value)
     /**
      * Get original attributes.
      */
-    public function originalAttributes()
+    public function originalAttributes(): array
     {
         return $this->original;
     }
@@ -158,7 +156,7 @@ public function originalAttributes()
      * Ideally should be called once right after retrieving data from
      * the database.
      */
-    public function syncOriginalAttributes()
+    public function syncOriginalAttributes(): void
     {
         $this->original = $this->attributes;
     }
@@ -166,12 +164,10 @@ public function syncOriginalAttributes()
     /**
      * Verify if model has a mutator method defined.
      *
-     * @param mixed $key    attribute name
+     * @param string $key    attribute name
      * @param mixed $prefix method prefix to be used
-     *
-     * @return bool
      */
-    protected function hasMutatorMethod($key, $prefix)
+    protected function hasMutatorMethod(string $key, mixed $prefix): bool
     {
         $method = $this->buildMutatorMethod($key, $prefix);
 
@@ -181,22 +177,20 @@ protected function hasMutatorMethod($key, $prefix)
     /**
      * Create mutator method pattern.
      *
-     * @param mixed $key    attribute name
+     * @param string $key    attribute name
      * @param mixed $prefix method prefix to be used
      *
      * @return string
      */
-    protected function buildMutatorMethod($key, $prefix)
+    protected function buildMutatorMethod(string $key, mixed $prefix): string
     {
         return $prefix.ucfirst($key).'Attribute';
     }
 
     /**
      * Returns the model instance as an Array.
-     *
-     * @return array
      */
-    public function toArray()
+    public function toArray(): array
     {
         return $this->getAttributes();
     }
@@ -204,11 +198,9 @@ public function toArray()
     /**
      * Dynamically retrieve attributes on the model.
      *
-     * @param mixed $key name of the attribute
-     *
-     * @return mixed
+     * @param string $key name of the attribute
      */
-    public function __get($key)
+    public function __get(string $key): mixed
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'get')) {
             return $this->{$this->buildMutatorMethod($key, 'get')}();
@@ -220,10 +212,10 @@ public function __get($key)
     /**
      * Dynamically set attributes on the model.
      *
-     * @param mixed $key   attribute name
+     * @param string $key   attribute name
      * @param mixed $value value to be set
      */
-    public function __set($key, $value)
+    public function __set(string $key, mixed $value): void
     {
         if ($this->mutable && $this->hasMutatorMethod($key, 'set')) {
             $value = $this->{$this->buildMutatorMethod($key, 'set')}($value);
@@ -236,10 +228,8 @@ public function __set($key, $value)
      * Determine if an attribute exists on the model.
      *
      * @param mixed $key attribute name
-     *
-     * @return bool
      */
-    public function __isset($key)
+    public function __isset(mixed $key):bool
     {
         return !is_null($this->{$key});
     }
@@ -249,7 +239,7 @@ public function __isset($key)
      *
      * @param mixed $key attribute name
      */
-    public function __unset($key)
+    public function __unset(string $key):void
     {
         unset($this->attributes[$key]);
     }
@@ -265,7 +255,7 @@ public function hasDocumentAttribute(string $key): bool
         return $this->hasAttribute($key);
     }
 
-    public function getDocumentAttribute(string $key)
+    public function getDocumentAttribute(string $key): mixed
     {
         return $this->getAttribute($key);
     }
@@ -284,12 +274,12 @@ public function cleanDocumentAttribute(string $key): void
         }
     }
 
-    public function setDocumentAttribute(string $key, $value): void
+    public function setDocumentAttribute(string $key, mixed $value): void
     {
         $this->setAttribute($key, $value);
     }
 
-    public function syncOriginalDocumentAttributes()
+    public function syncOriginalDocumentAttributes(): void
     {
         $this->syncOriginalAttributes();
     }
diff --git a/src/Model/Relations/AbstractRelation.php b/src/Model/Relations/AbstractRelation.php
index a6379990..e45e249d 100644
--- a/src/Model/Relations/AbstractRelation.php
+++ b/src/Model/Relations/AbstractRelation.php
@@ -6,58 +6,31 @@
 
 abstract class AbstractRelation implements RelationInterface
 {
-    /**
-     * @var ModelInterface
-     */
-    protected $parent;
-
-    /**
-     * @var string
-     */
-    protected $model;
-
-    /**
-     * @var string
-     */
-    protected $field;
-
-    /**
-     * @var bool
-     */
-    protected $pristine = false;
+    protected bool $pristine = false;
 
     /**
      * Cached results.
-     *
-     * @var mixed
      */
-    protected $results;
+    protected mixed $results;
 
-    /**
-     * @var string
-     */
-    protected $key = '_id';
+    protected string $key = '_id';
 
-    public function __construct(ModelInterface $parent, string $model, string $field)
-    {
-        $this->parent = $parent;
-        $this->model = $model;
-        $this->field = $field;
+    public function __construct(
+        protected ModelInterface $parent,
+        protected string $model,
+        protected string $field
+    ){
     }
 
     /**
      * Retrieve Relation Results.
-     *
-     * @return mixed
      */
-    abstract public function get();
+    abstract public function get(): mixed;
 
     /**
      * Retrieve cached Relation Results.
-     *
-     * @return mixed
      */
-    public function &getResults()
+    public function &getResults(): mixed
     {
         if (!$this->pristine()) {
             $this->results = $this->get();
@@ -77,10 +50,8 @@ protected function pristine(): bool
      * a new key will be generated and set on the model (while still returning it).
      *
      * @param ModelInterface $model the object that the key will be retrieved from
-     *
-     * @return ObjectId|mixed
      */
-    protected function getKey(ModelInterface $model)
+    protected function getKey(ModelInterface $model): mixed
     {
         if (!$model->{$this->key}) {
             $model->{$this->key} = new ObjectId();
diff --git a/src/Model/Relations/EmbedsMany.php b/src/Model/Relations/EmbedsMany.php
index fdfe015a..b083d011 100644
--- a/src/Model/Relations/EmbedsMany.php
+++ b/src/Model/Relations/EmbedsMany.php
@@ -34,8 +34,6 @@ public function addMany(array $entities): void
 
     /**
      * Replace embedded documents.
-     *
-     * @param array $entities
      */
     public function replace(array $entities): void
     {
@@ -69,10 +67,7 @@ public function removeAll(): void
         $this->pristine = false;
     }
 
-    /**
-     * @return EmbeddedCursor
-     */
-    public function get()
+    public function get(): EmbeddedCursor
     {
         $items = $this->parent->{$this->field} ?? [];
 
diff --git a/src/Model/Relations/EmbedsOne.php b/src/Model/Relations/EmbedsOne.php
index 1a18d864..ce6831f7 100644
--- a/src/Model/Relations/EmbedsOne.php
+++ b/src/Model/Relations/EmbedsOne.php
@@ -17,10 +17,7 @@ public function remove(): void
         $this->pristine = false;
     }
 
-    /**
-     * @return ModelInterface|null
-     */
-    public function get()
+    public function get(): ?ModelInterface
     {
         return $this->parent->{$this->field};
     }
diff --git a/src/Model/Relations/ReferencesMany.php b/src/Model/Relations/ReferencesMany.php
index 12247b02..7919980c 100644
--- a/src/Model/Relations/ReferencesMany.php
+++ b/src/Model/Relations/ReferencesMany.php
@@ -3,15 +3,13 @@
 
 use MongoDB\BSON\ObjectId;
 use Mongolid\Container\Container;
+use Mongolid\Cursor\CursorInterface;
 use Mongolid\Model\ModelInterface;
 use Mongolid\Util\ObjectIdUtils;
 
 class ReferencesMany extends AbstractRelation
 {
-    /**
-     * @var ModelInterface
-     */
-    protected $modelInstance;
+    protected ModelInterface $modelInstance;
 
     public function __construct(ModelInterface $parent, string $model, string $field, string $key)
     {
@@ -29,10 +27,8 @@ public function attach(ModelInterface $model): void
         $referencedKey = $this->getKey($model);
         $fieldValue = (array) $this->parent->{$this->field};
 
-        foreach ($fieldValue as $key) {
-            if ($key == $referencedKey) {
-                return;
-            }
+        if (in_array($referencedKey, $fieldValue)) {
+            return;
         }
 
         $fieldValue[] = $referencedKey;
@@ -89,7 +85,7 @@ public function detachAll(): void
         $this->pristine = false;
     }
 
-    public function get()
+    public function get(): CursorInterface
     {
         $referencedKeys = (array) $this->parent->{$this->field};
 
diff --git a/src/Model/Relations/ReferencesOne.php b/src/Model/Relations/ReferencesOne.php
index 2fb017ee..f689d889 100644
--- a/src/Model/Relations/ReferencesOne.php
+++ b/src/Model/Relations/ReferencesOne.php
@@ -8,10 +8,7 @@
 
 class ReferencesOne extends AbstractRelation
 {
-    /**
-     * @var ModelInterface
-     */
-    protected $modelInstance;
+    protected ModelInterface $modelInstance;
 
     public function __construct(ModelInterface $parent, string $model, string $field, string $key)
     {
@@ -32,7 +29,7 @@ public function detach(): void
         $this->pristine = false;
     }
 
-    public function get()
+    public function get(): ?ModelInterface
     {
         if (!$referencedKey = $this->parent->{$this->field}) {
             return null;
diff --git a/src/Model/Relations/RelationInterface.php b/src/Model/Relations/RelationInterface.php
index 425e3ea9..789b1621 100644
--- a/src/Model/Relations/RelationInterface.php
+++ b/src/Model/Relations/RelationInterface.php
@@ -5,8 +5,6 @@ interface RelationInterface
 {
     /**
      * Get the results of the relation.
-     *
-     * @return mixed
      */
-    public function getResults();
+    public function getResults(): mixed;
 }
diff --git a/tests/Stubs/EmbeddedUser.php b/tests/Stubs/EmbeddedUser.php
index 0d82cef4..e6fb6d56 100644
--- a/tests/Stubs/EmbeddedUser.php
+++ b/tests/Stubs/EmbeddedUser.php
@@ -5,15 +5,9 @@
 
 class EmbeddedUser extends AbstractModel
 {
-    /**
-     * @var string
-     */
-    protected $collection = 'users';
-
-    /**
-     * @var bool
-     */
-    protected $timestamps = true;
+    protected ?string $collection = 'users';
+
+    protected bool $timestamps = true;
 
     public function parent()
     {
diff --git a/tests/Stubs/Legacy/LegacyRecordUser.php b/tests/Stubs/Legacy/LegacyRecordUser.php
index 3265e86c..e36792a1 100644
--- a/tests/Stubs/Legacy/LegacyRecordUser.php
+++ b/tests/Stubs/Legacy/LegacyRecordUser.php
@@ -1,6 +1,7 @@
 <?php
 namespace Mongolid\Tests\Stubs\Legacy;
 
+use Mongolid\Cursor\CursorInterface;
 use Mongolid\LegacyRecord;
 
 class LegacyRecordUser extends LegacyRecord
@@ -10,10 +11,7 @@ class LegacyRecordUser extends LegacyRecord
      */
     protected $collection = 'users';
 
-    /**
-     * @var bool
-     */
-    public $mutable = true;
+    public bool $mutable = true;
 
     /**
      * @var bool
@@ -25,24 +23,21 @@ class LegacyRecordUser extends LegacyRecord
      */
     public $dynamic = false;
 
-    /**
-     * @var string[]
-     */
-    protected $fillable = [
+    protected array $fillable = [
         'name',
     ];
 
-    public function siblings()
+    public function siblings(): CursorInterface
     {
         return $this->embedsMany(LegacyRecordUser::class, 'siblings');
     }
 
-    public function grandsons()
+    public function grandsons(): array
     {
         return $this->referencesMany(LegacyRecordUser::class, 'grandsons');
     }
 
-    public function setSecretAttribute($value)
+    public function setSecretAttribute($value): string
     {
         return 'password_override';
     }
diff --git a/tests/Stubs/Legacy/Product.php b/tests/Stubs/Legacy/Product.php
index 71ab93fe..b26129bb 100644
--- a/tests/Stubs/Legacy/Product.php
+++ b/tests/Stubs/Legacy/Product.php
@@ -1,6 +1,8 @@
 <?php
 namespace Mongolid\Tests\Stubs\Legacy;
 
+use Illuminate\Contracts\Container\BindingResolutionException;
+use Mongolid\Cursor\CursorInterface;
 use Mongolid\LegacyRecord;
 use Mongolid\Tests\Stubs\Price;
 
@@ -22,12 +24,15 @@ class Product extends LegacyRecord
         ],
     ];
 
-    public function price()
+    /**
+     * @throws BindingResolutionException
+     */
+    public function price(): mixed
     {
         return $this->referencesOne(Price::class, '_id');
     }
 
-    public function skus()
+    public function skus(): CursorInterface
     {
         return $this->embedsMany(Sku::class, 'skus');
     }
diff --git a/tests/Stubs/Legacy/Sku.php b/tests/Stubs/Legacy/Sku.php
index a680181c..f7b9825c 100644
--- a/tests/Stubs/Legacy/Sku.php
+++ b/tests/Stubs/Legacy/Sku.php
@@ -1,11 +1,15 @@
 <?php
 namespace Mongolid\Tests\Stubs\Legacy;
 
+use Illuminate\Contracts\Container\BindingResolutionException;
 use Mongolid\LegacyRecord;
 
 class Sku extends LegacyRecord
 {
-    public function shop()
+    /**
+     * @throws BindingResolutionException
+     */
+    public function shop(): mixed
     {
         return $this->referencesOne(Shop::class, 'shop_id');
     }
diff --git a/tests/Stubs/PolymorphedReferencedUser.php b/tests/Stubs/PolymorphedReferencedUser.php
index d6a0c8a0..e3871493 100644
--- a/tests/Stubs/PolymorphedReferencedUser.php
+++ b/tests/Stubs/PolymorphedReferencedUser.php
@@ -3,10 +3,7 @@
 
 class PolymorphedReferencedUser extends ReferencedUser
 {
-    /**
-     * {@inheritdoc}
-     */
-    protected $fillable = [
+    protected array $fillable = [
         'type',
         'new_field',
     ];
diff --git a/tests/Stubs/Price.php b/tests/Stubs/Price.php
index e079222a..c44aec57 100644
--- a/tests/Stubs/Price.php
+++ b/tests/Stubs/Price.php
@@ -5,8 +5,5 @@
 
 class Price extends AbstractModel
 {
-    /**
-     * @var string
-     */
-    protected $collection = 'prices';
+    protected ?string $collection = 'prices';
 }
diff --git a/tests/Stubs/Product.php b/tests/Stubs/Product.php
index f905b581..96b5b8c8 100644
--- a/tests/Stubs/Product.php
+++ b/tests/Stubs/Product.php
@@ -5,8 +5,5 @@
 
 class Product extends AbstractModel
 {
-    /**
-     * @var string
-     */
-    protected $collection = 'products';
+    protected ?string $collection = 'products';
 }
diff --git a/tests/Stubs/ReferencedUser.php b/tests/Stubs/ReferencedUser.php
index 71cc5a04..ad693a7f 100644
--- a/tests/Stubs/ReferencedUser.php
+++ b/tests/Stubs/ReferencedUser.php
@@ -3,49 +3,42 @@
 
 use Mongolid\Model\AbstractModel;
 use Mongolid\Model\PolymorphableModelInterface;
+use Mongolid\Model\Relations\ReferencesMany;
+use Mongolid\Model\Relations\ReferencesOne;
 
 class ReferencedUser extends AbstractModel implements PolymorphableModelInterface
 {
-    /**
-     * @var string
-     */
-    protected $collection = 'users';
+    protected ?string $collection = 'users';
 
-    /**
-     * @var bool
-     */
-    protected $timestamps = false;
+    protected bool $timestamps = false;
 
-    /**
-     * {@inheritdoc}
-     */
-    protected $fillable = [
+    protected array $fillable = [
         'type',
         'exclusive',
         'other_exclusive',
     ];
 
-    public function parent()
+    public function parent(): ReferencesOne
     {
         return $this->referencesOne(ReferencedUser::class);
     }
 
-    public function siblings()
+    public function siblings(): ReferencesMany
     {
         return $this->referencesMany(ReferencedUser::class);
     }
 
-    public function son()
+    public function son(): ReferencesOne
     {
         return $this->referencesOne(ReferencedUser::class, 'arbitrary_field', 'code');
     }
 
-    public function grandsons()
+    public function grandsons(): ReferencesMany
     {
         return $this->referencesMany(ReferencedUser::class, null, 'code');
     }
 
-    public function invalid()
+    public function invalid(): string
     {
         return 'I am not a relation!';
     }
diff --git a/tests/Stubs/ReplaceCollectionModel.php b/tests/Stubs/ReplaceCollectionModel.php
index c40ecf2a..9245b3d0 100644
--- a/tests/Stubs/ReplaceCollectionModel.php
+++ b/tests/Stubs/ReplaceCollectionModel.php
@@ -6,20 +6,11 @@
 
 class ReplaceCollectionModel extends AbstractModel
 {
-    /**
-     * {@inheritdoc}
-     */
-    protected $timestamps = false;
+    protected bool $timestamps = false;
 
-    /**
-     * {@inheritdoc}
-     */
-    protected $collection = 'models';
+    protected ?string $collection = 'models';
 
-    /**
-     * @var Collection
-     */
-    protected $rawCollection;
+    protected Collection $rawCollection;
 
     public function setCollection(Collection $collection): void
     {
diff --git a/tests/Unit/Model/AbstractModelTest.php b/tests/Unit/Model/AbstractModelTest.php
index 4eb4b280..a6e2a71f 100644
--- a/tests/Unit/Model/AbstractModelTest.php
+++ b/tests/Unit/Model/AbstractModelTest.php
@@ -29,12 +29,9 @@ protected function setUp(): void
         parent::setUp();
         $this->model = new class() extends AbstractModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            protected $collection = 'mongolid';
+            protected ?string $collection = 'mongolid';
 
-            public function unsetCollection()
+            public function unsetCollection(): void
             {
                 unset($this->collection);
             }
@@ -482,10 +479,7 @@ public function testShouldCheckIfMutatedAttributeIsSet(): void
         // Set
         $model = new class() extends AbstractModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            public $mutable = true;
+            public bool $mutable = true;
 
             public function getNameDocumentAttribute(): string
             {
@@ -524,10 +518,7 @@ public function testShouldGetAttributeFromMutator(): void
         // Set
         $model = new class() extends AbstractModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            public $mutable = true;
+            public bool $mutable = true;
 
             public function getShortNameDocumentAttribute(): string
             {
@@ -571,10 +562,7 @@ public function testShouldSetAttributeFromMutator(): void
         // Set
         $model = new class() extends AbstractModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            protected $mutable = true;
+            protected bool $mutable = true;
 
             public function setShortNameDocumentAttribute($value): string
             {
diff --git a/tests/Unit/Model/HasAttributesTraitTest.php b/tests/Unit/Model/HasAttributesTraitTest.php
index 87955de4..29faa979 100644
--- a/tests/Unit/Model/HasAttributesTraitTest.php
+++ b/tests/Unit/Model/HasAttributesTraitTest.php
@@ -368,12 +368,9 @@ public function testShouldCheckIfMutatedAttributeIsSet(): void
         // Set
         $model = new class() extends AbstractModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            public $mutable = true;
+            public bool $mutable = true;
 
-            public function getNameDocumentAttribute()
+            public function getNameDocumentAttribute(): string
             {
                 return 'John';
             }
diff --git a/tests/Unit/Model/HasLegacyRelationTraitTest.php b/tests/Unit/Model/HasLegacyRelationTraitTest.php
index c02c5725..0ccd73ef 100644
--- a/tests/Unit/Model/HasLegacyRelationTraitTest.php
+++ b/tests/Unit/Model/HasLegacyRelationTraitTest.php
@@ -19,7 +19,6 @@ public function testReferenceOneShouldNotHitCache($fieldValue, array $expectedQu
         // Set
         $model = new Product();
         $model->_id = $fieldValue;
-        $expected = new Price();
         $priceModel = $this->instance(Price::class, m::mock(Price::class)->makePartial());
         $cacheComponent = $this->instance(
             CacheComponentInterface::class,
@@ -33,13 +32,13 @@ public function testReferenceOneShouldNotHitCache($fieldValue, array $expectedQu
 
         $priceModel->expects('first')
             ->with($expectedQuery, [], true)
-            ->andReturn($expected);
+            ->andReturnSelf();
 
         // Actions
         $result = $model->price();
 
         // Assertions
-        $this->assertSame($expected, $result);
+        $this->assertSame($priceModel, $result);
     }
 
     /**
diff --git a/tests/Unit/Query/BuilderTest.php b/tests/Unit/Query/BuilderTest.php
index 413e995a..031dd55a 100644
--- a/tests/Unit/Query/BuilderTest.php
+++ b/tests/Unit/Query/BuilderTest.php
@@ -245,18 +245,12 @@ public function testShouldUpdateUnsettingFields(): void
 
         $model = new class() extends ReplaceCollectionModel
         {
-            /**
-             * {@inheritdoc}
-             */
-            public $fillable = [
+            public array $fillable = [
                 'name',
                 'unchanged',
             ];
 
-            /**
-             * {@inheritdoc}
-             */
-            protected $dynamic = false;
+            protected bool $dynamic = false;
         };
         $collection = m::mock(Collection::class);
         $operationResult = m::mock();