How I can get entitymanager from crudrepository

I use Spring Boot and want to improve perfomance. I must download file with 50000 field in database. Use hibernate. I found solution in Batch inserts. But I don't know how get entitymanager from crudrepository

public interface MyRepository extends CrudRepository<OTA, Long>

application.yaml
                jdbc.batch_size: 50
                order_inserts: true
                order_updates: true
                cache.use_second_level_cache: true

I creatred MyStorageService and want to save my file:

@Service @Repository @Transactional public class MyStorageService {
    private MyRepository myRepository;

    private void insertAll(final List<MyFile> file) {
        myRepository.save(file.getListLine());
    } 

private void insert(final List<OTA> ota) {
    Session session = (Session) entityManager.getDelegate();

    Transaction tx = session.beginTransaction();

    for (int i = 0; i < ota.size(); i++) {
        session.save(ota.get(i));
        if (i % 50 == 0) {
            session.flush();
            session.clear();
        }
    }

    tx.commit();
    session.close();
}

}

If use in MyStorageService

@PersistenceContext
EntityManager entityManager;

I get

ERROR [http-nio-18842-exec-1] JpaTransactionManager: Commit exception overridden by rollback exception java.lang.IllegalStateException: Transaction not active at org.hibernate.jpa.internal.TransactionImpl.getRollbackOnly(TransactionImpl.java:131) at org.springframework.orm.jpa.JpaTransactionManager$JpaTransactionObject.isRollbackOnly(JpaTransactionManager.java:665)

ERROR [http-nio-18842-exec-1] JpaTransactionManager: Commit exception overridden by rollback exception java.lang.IllegalStateException: Transaction not active at org.hibernate.jpa.internal.TransactionImpl.getRollbackOnly(TransactionImpl.java:131) at org.springframework.orm.jpa.JpaTransactionManager$JpaTransactionObject.isRollbackOnly(JpaTransactionManager.java:665)

If

@Autowired
EntityManager entityManager;

I get

ERROR [http-nio-18842-exec-5] JpaTransactionManager: Commit exception overridden by rollback exception java.lang.IllegalStateException: Transaction not active at org.hibernate.jpa.internal.TransactionImpl.getRollbackOnly(TransactionImpl.java:131) at org.springframework.orm.jpa.JpaTransactionManager$JpaTransactionObject.isRollbackOnly(JpaTransactionManager.java:665)

java.lang.IllegalStateException: EntityManager is closed at org.hibernate.jpa.internal.EntityManagerImpl.checkOpen(EntityManagerImpl.java:97) at org.hibernate.jpa.internal.EntityManagerImpl.checkOpen(EntityManagerImpl.java:88) at org.hibernate.jpa.spi.AbstractEntityManagerImpl.clear(AbstractEntityManagerImpl.java:1382) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:347) at com.sun.proxy.$Proxy91.clear(Unknown Source) at org.springframework.orm.jpa.JpaTransactionManager.doRollback(JpaTransactionManager.java:554)

I use base method savefrom crud repository, but want to improve perfomance and use insert. Tell me please how get entitymanager from crudrepository.
Thanks