public function getRelationshipKey($field)
	{
		$model = $this->config->getDataModel();
		$invalidArgument = new \InvalidArgumentException("The '" . $field . "' relationship field you supplied for " .
								$this->config->getOption('name') . " is not a valid relationship method name on the supplied Eloquent model");

		//check if the related method exists on the model
		if (!method_exists($model, $field))
		{
			throw $invalidArgument;
		}

		//now that we know the method exists, we can determine if it's multiple or single
		$related_model = $model->{$field}();

		//check if this is a valid relationship object, and return the appropriate key
		if (is_a($related_model, $this->relationshipBase.'BelongsTo'))
		{
			return 'belongs_to';
		}
		else if (is_a($related_model, $this->relationshipBase.'BelongsToMany'))
		{
			return 'belongs_to_many';
		}
		else if (is_a($related_model, $this->relationshipBase.'HasOne'))
		{
			return 'has_one';
		}
		else if (is_a($related_model, $this->relationshipBase.'HasMany'))
		{
			return 'has_many';
		}
		else
		{
			throw $invalidArgument;
		}
	}