Java Stream：如何通过集合映射子实体？

Question

我有以下实体和 DTO：

public class Customer {

    private Long id;

    private String name;

    @OneToMany(mappedBy = "customer", cascade = CascadeType.ALL)
    private Set<Account> accounts = new HashSet<>();

    // getter, setter, constructors
}

我正在尝试通过映射 customer.getAccounts().getBalance() 和 customer.getAccounts().getTransactions() 将此实体列表映射到以下 DTO，如下所示：

@Data
public class CustomerResponse {

    private Long id;

    private String name;

    private BigDecimal balance;

    private List<TransactionResponse> transactions;

    public CustomerResponse(Customer customer, Set<Account> accounts) {
        this.id = customer.getId();
        this.name = customer.getName();

        // ???
        this.balance = accounts...
        this.transactions = customer.getAccounts()...
    }
}

但是我无法映射，我不知道我是否可以在下面的服务方法中映射它们：

public List<CustomerResponse> findAll() {
    final List<CustomerResponse> customers = customerRepository.findAll().stream()
            .map(customer -> new CustomerResponse(customer, customer.getAccounts())).toList();
    
    return customers;
}

那么，我怎样才能为每个客户正确映射 balance 和 transactions？

这里是其他实体（为简洁起见省略了@Id和一些其他注释）：

public class Account {

    private Long id;

    private BigDecimal balance;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "customer_id", referencedColumnName = "id")
    private Customer customer;

    @OneToMany(mappedBy = "account", cascade = CascadeType.ALL)
    private Set<Transaction> transactions = new HashSet<>();

    // code omitted
}

public class Transaction {

    private Long id;

    private LocalDateTime date;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "account_id", referencedColumnName = "id")
    private Account account;
}