Improve DX for dynamically adding relationships

This improves the developer experience for dynamically adding relationships to an external model when extending the model. Previously the developer would have to set the relation property directly themselves by merging their additions with the existing definitions and usually they wouldn't include any error checking logic.

src/Database/Concerns/HasRelationships.php

@@ -134,7 +134,6 @@ trait HasRelationships
         'hasManyThrough'
     ];
 
-
     //
     // Relations
     //
@@ -785,4 +784,164 @@ protected function setRelationValue($relationName, $value)
     {
         $this->$relationName()->setSimpleValue($value);
     }
+
+     /**
+     * Dynamically add the provided relationship configuration to the local properties
+     *
+     * @throws InvalidArgumentException if the $type is invalid or if the $name is already in use
+     */
+    protected function addRelation(string $type, string $name, array $config): void
+    {
+        if (!in_array($type, static::$relationTypes)) {
+            throw new InvalidArgumentException(
+                sprintf('Cannot add the "%s" relation to %s, %s is not a valid relationship type.',
+                    $name,
+                    get_class($this),
+                    $type
+                )
+            );
+        }
+
+        if ($this->hasRelation($name) || isset($this->{$name})) {
+            throw new InvalidArgumentException(
+                sprintf('Cannot add the "%s" relation to %s, it conflicts with an existing relation, attribute, or property.',
+                    $name,
+                    get_class($this),
+                    $name
+                )
+            );
+        }
+
+        $this->{$type} = array_merge($this->{$type}, [$name => $config]);
+    }
+
+    /**
+     * Dynamically add a HasOne relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addHasOneRelation(string $name, array $config): void
+    {
+        $this->addRelation('hasOne', $name, $config);
+    }
+
+    /**
+     * Dynamically add a HasMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addHasManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('hasMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add a BelongsTo relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addBelongsToRelation(string $name, array $config): void
+    {
+        $this->addRelation('belongsTo', $name, $config);
+    }
+
+    /**
+     * Dynamically add a BelongsToMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addBelongsToManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('belongsToMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add a MorphTo relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addMorphToRelation(string $name, array $config): void
+    {
+        $this->addRelation('morphTo', $name, $config);
+    }
+
+    /**
+     * Dynamically add a MorphOne relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addMorphOneRelation(string $name, array $config): void
+    {
+        $this->addRelation('morphOne', $name, $config);
+    }
+
+    /**
+     * Dynamically add a MorphMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addMorphManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('morphMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add a MorphToMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addMorphToManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('morphToMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add a MorphedByMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addMorphedByManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('morphedByMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add an AttachOne relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addAttachOneRelation(string $name, array $config): void
+    {
+        $this->addRelation('attachOne', $name, $config);
+    }
+
+    /**
+     * Dynamically add an AttachMany relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addAttachManyRelation(string $name, array $config): void
+    {
+        $this->addRelation('attachMany', $name, $config);
+    }
+
+    /**
+     * Dynamically add a(n) HasOneThrough relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addHasOneThroughRelation(string $name, array $config): void
+    {
+        $this->addRelation('HasOneThrough', $name, $config);
+    }
+
+    /**
+     * Dynamically add a(n) HasManyThrough relationship
+     *
+     * @throws InvalidArgumentException if the provided relationship is already defined
+     */
+    public function addHasManyThroughRelation(string $name, array $config): void
+    {
+        $this->addRelation('HasManyThrough', $name, $config);
+    }
 }