private function write_definitions_to_cache(array $definitions) {

        // Preserve the selected sharing option when updating the definitions.
        // This is set by the user and should never come from caches.php.
        foreach ($definitions as $key => $definition) {
            unset($definitions[$key]['selectedsharingoption']);
            unset($definitions[$key]['userinputsharingkey']);
            if (isset($this->configdefinitions[$key]) && isset($this->configdefinitions[$key]['selectedsharingoption'])) {
                $definitions[$key]['selectedsharingoption'] = $this->configdefinitions[$key]['selectedsharingoption'];
            }
            if (isset($this->configdefinitions[$key]) && isset($this->configdefinitions[$key]['userinputsharingkey'])) {
                $definitions[$key]['userinputsharingkey'] = $this->configdefinitions[$key]['userinputsharingkey'];
            }
        }

        $this->configdefinitions = $definitions;
        foreach ($this->configdefinitionmappings as $key => $mapping) {
            if (!array_key_exists($mapping['definition'], $definitions)) {
                unset($this->configdefinitionmappings[$key]);
            }
        }
        $this->config_save();
    }