How to get id of the inserted entity when using ViewModel?

The root problem: I want to set the id of [Entity A] in foreign key of [Entity B] but id of [Entity A] is not available until inserted in the database (because it is autogenerated by the DBMS).

Using architecture components (Room, ViewModel and LiveData), how can I perform a transaction that saves multiple related entities in the database? The following code currently resides in the ViewModel and works fine. The problem is I want to put this AsyncTask in the repository layer like other simple one-operation queries, but is it OK? Because in that case the repository would be responsible for managing relationships and knowing about entity details.

As I said above, the main problem is that I need id of the inserted entity so I can save it in another entity. If this requirement didn't exist, I would be able to persist each entity one by one in separate AsyncTasks in the repository.

MainViewModel.java:

public void buy(Item item, Store store) {

    new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... voids) {
            long storeId = mRepository.insertStore(store);

            Purchase purchase = new Purchase(storeId); // here uses id of the store
            long purchaseId = mRepository.insertPurchase(purchase);

            item.setPurchaseId(purchaseId); // here uses id of the purchase
            mRepository.updateItem(item);

            return null;
        }
    }.execute();
}

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