> For the complete documentation index, see [llms.txt](https://ankang.gitbook.io/commons/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ankang.gitbook.io/commons/commons-beans/gong-neng/di-gui-chu-li.md).

# 递归处理

对象拷贝作用于JPA中的实体时，可能会出现两个实体循环依赖的问题，导致序列化失败。原则上不建议在DTO层面定义循环依赖的关系，如果因为特殊原因无法避免，框架会自动将循环依赖的字段设置为`null`。

```java
class Foo {
    String name = "foo";
    @OneToMany
    List<Bar> bars;
}
class Bar {
    String name = "bar";
    @ManyToOne
    Foo foo;
}
class FooDto {
    String name;
    List<Bar> bars;
}

Foo foo = fooRepository.findById(1L);
FooDto fooDto = BeanUtils.copyProperties(foo, FooDto.class);

System.out.println(foo); // StackOverflowError
System.out.println(fooDto); 
/**
 * {
 *     "name": "foo",
 *     "bars": [
 *         {
 *             "name": "bar",
 *             "foo": null
 *         },
 *         ...
 *     ]
 * }
 */

```