External IDs
This section is only relevant if your users want to assign custom ids to their properties.
When publishing real estate listings online, brokers often use a custom id that is displayed besides the property. Interested customers can then refer to the property by giving this id to the broker. Within EstateSync this id is called externalId.
The externalId is different from the id that EstateSync generates for each property. It is also different from the id that targets might generate (e.g. the Scout-ID of ImmoScout24).
If you don't pass an externalId when creating a property EstateSync will generate a random id. This id cannot be changed after property creation because it is used to identify properties on most target platforms.
Providing a custom externalId
You can pass a custom externalId when creating the property. Because this id is used to identify properties on the target platform, it needs to be unique within the listings of a target.
So let's say you want to create a new listing of a property on a target. EstateSync will validate that there is no other property with the same externalId that also has a listing with your target. The check will also include properties that had a listing with your target in the past. This is to ensure that data on the target platform is not accidentally overwritten.
What matters for your implementation
When allowing your users to provide a custom externalId you should make sure that it is unique within all properties that are going to be published on a specific target.