# defineEntityId
This composable is used in useEntity to define the entityId based on the given entity.
/customers/123-456/contacts/567-890
When you give customers the next slug is used: 123-456. When you give entity contacts the entityId is 567-890.
/customers/123-456/contacts/new/customers/123-456/contacts
Based on these two routes the entityId is undefined.
TIP
The entityId is automatically updated when the route changes, because of the reactive bindings in Vue.