I had this problem, I needed to inject a Storage to my controller so I can create a custom action and connect to my db using a storage service.

All I needed was configure the services as following:
[cc_yaml]
services:
app.admin.document:
class: AppBundle\Admin\DocumentAdmin
arguments: [~, AppBundle\Entity\Document, ‘app.controller.document’]
tags:
– { name: sonata.admin, manager_type: orm, group: Documentation, label: Documents }

app.controller.document:
class: AppBundle\Controller\DocumentAdminController
calls:
– [ setContainer,[ “@service_container” ] ]
arguments:
– “@security.token_storage”
– “@app.storage.document”

app.repository.document:
class: AppBundle\Repository\DocumentRepository
factory: [“@doctrine.orm.entity_manager”, getRepository]
arguments:
– AppBundle\Entity\Document

app.storage.document:
class: AppBundle\Storage\DocumentStorage
arguments:
– “@app.repository.document”
[/cc_yaml]