purge_nexus_v3_releases.groovy

import org.sonatype.nexus.repository.storage.StorageFacet;
import org.sonatype.nexus.repository.storage.Query;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;

def fmt = DateTimeFormat.forPattern('yyyy-MM-dd HH:mm:ss');
// Get a repository
def repo = repository.repositoryManager.get('nuget-releases');
// Get a database transaction
def tx = repo.facet(StorageFacet).txSupplier().get();
// Begin the transaction
tx.begin();
// Search assets that havn't been downloaded for more than three months
tx.findAssets(Query.builder().where('last_downloaded <').param(DateTime.now().minusMonths(3).toString(fmt)).build(), [repo]).each { asset ->
	def component = tx.findComponent(asset.componentId());
	// Check if there is newer components of the same name
	def count = tx.countComponents(Query.builder().where('name').eq(component.name()).and('version >').param(component.version()).build(), [repo]);
	if (count > 0) {
		log.info("Delete asset ${asset.name()} as it has not been downloaded since 3 months and has a newer version")
		tx.deleteAsset(asset);
		tx.deleteComponent(component);
	}
}
// End the transaction
tx.commit();

For those wondering, you need to run a Compact blob store task to actually free up the local storage.