protected function _getField() {
        //We can access to a field of the current Entity or a linked Entity (foreign key)
        //If the field name contain a "." it's the second case
        $fields = [];
        $fieldsData = $this->_entity->fields();

        //We have to analyze a classic field without linked Entity
        if (!preg_match('#\.#isU', $this->_field)) {
            if (isset($fieldsData[$this->_field])) {
                $fields = [$fieldsData[$this->_field]->value];
            }
            else {
                throw new MissingEntityException('The field "' . $this->_field . '" in the Entity "' . $this->_entity->name() . '" does\'nt exist');
            }
        }
        else {
            //Here it's sure that we have a linked Entity. But we don't compute "One to One and One to Many" in the same way than the 2 other
            //because in the two first the field value is an Entity object and in the two other, the field value is a Collection
            //To know which type of linked Entity it's, we just split the name on the "." and we take the index 0 of the generated array

            $entityName = explode('.', $this->_field);

            if (array_key_exists($entityName[0], $fieldsData) && $fieldsData[$entityName[0]]->foreign != null) {
                /** @var int $foreignType : the type of the foreign key */
                $foreignType = $fieldsData[$entityName[0]]->foreign->type();
                /** @var mixed $fieldValue : the value of the sub-field from the Entity (post.article.content->value) */
                $fieldValue = $fieldsData[$entityName[0]]->value->fields()[$entityName[1]];

                if ($foreignType == ForeignKey::ONE_TO_MANY || $foreignType == ForeignKey::MANY_TO_ONE) {
                    $fields = $this->_getForeignKeyFieldValue($fieldValue);
                }
                else { //We must get all the sub entities as an array an then loop through this array to get the field values
                    foreach ($fieldValue->data() as $fieldValueCollection) {
                        $fields = array_merge($fields, $this->_getForeignKeyFieldValue($fieldValueCollection));
                    }
                }
            }
            else {
                throw new MissingEntityException('The field "' . $this->_field . '" in the Entity "' . $this->_entity->name() . '" does\'nt exist');
            }
        }

        return $fields;
    }