Spring JPA 投影可以有集合吗?

问题描述

我有一个 Customer 实体，我只想从中选择几个字段及其关联的 CustomerAddresses.我已经定义了一个 Spring Data JPA 投影接口如下:

I have a Customer entity from which I only want to select a few fields and their associated CustomerAddresses. I've defined a Spring Data JPA projection interface as follows:

public interface CustomerWithAddresses {
    Integer getId();
    String getFirstName();
    String getLastName();
    String getBrandCode();
    String getCustomerNumber();
    Set<CustomerAddress> getCustomerAddresses();
}

但是从我的 Repository 方法:

But from my Repository method:

CustomerWithAddresses findCustomerWithAddressesById(@Param("id") Integer id);

对于具有多个 CustomerAddress 的客户，我不断收到 NonUniqueResultException.投影是否必须具有扁平结构，即它们不像真正的实体那样支持集合?

I keep getting NonUniqueResultException for Customers with multiple CustomerAddresses. Do projections have to have a flat structure, i.e. they don't support Collections the same way true Entities do?

推荐答案

you have SetgetCustomerAddresses(); 它是 X 对多的关系.当 spring 数据确实为 CustomerWithAddresses 选择时，它确实加入了结果集中的 N 条记录(N - 为 CustomerWithAddresses 的 CustomerAddress 数量，id = id).您可以检查是否将 CustomerWithAddresses 更改为 List of CustomerWithAddresses .

you have Set<CustomerAddress> getCustomerAddresses(); it's X-to-Many relation. When spring data do select for CustomerWithAddresses it does join , in result set N-records (N - amount of CustomerAddress for CustomerWithAddresses with id = id). You can check if it you change CustomerWithAddresses to List of CustomerWithAddresses .

List<CustomerWithAddresses> findCustomerWithAddressesById(@Param("id") Integer id);

当您使用实体 sping 数据 gropu 将结果乘以一个元素时，将其按 id 排列为 id，这是唯一标识符.

when you use entity sping data gropu multiply result into one element , gouped it by id as id it's unique identifier.

你可以这样做:

1) 添加到 CustomerWithAddresses 接口中

1) add into CustomerWithAddresses interface

@Value("#{target.id}")
Integer getId();

并使用您的查询

2) 使用@Query

2) use @Query

@Query("select adr from CustomerWithAddressesEntity adr where adr.id=:id")
CustomerWithAddresses findCustomerWithAddressesById(@Param("id") Integer id);

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