英文:
How does map from Page from Spring data works?
问题
正如标题所述，org.springframework.data.domain.Page 中的 map 方法是如何工作的？
根据文档，它建议您将转换器作为 map 参数，然后您会获得一个包含转换内容的新映射。根据这种解释，我编写了以下代码。
Page<T> results = getPagedResults();
return results.map(x -> {
x.setElement("some constant");
return x;
});
然而，上述代码并没有按预期工作。我得到了一个页面，其中包含所有其他值，如计数等，但内容是一个空列表！我实际上不得不以这种方式编写代码。
Page<T> results = getPagedResults();
return new Page<T>() {
@Override
public int getTotalPages() {
return results.getTotalPages();
}
...
@Override
public List<T> getContent() {
List<T> contents = result.getContent();
for (T content : contents) {
content.setElement("some constant");
}
return contents;
}
...
};
第二种选择冗长，似乎做了冗余的工作。我本来期望第一段代码能够实现相同的功能，但实际上并没有。
我是否误解了文档？如果不能像我使用的方式那样使用 Page 的 map 函数，那么在什么情况下会使用它呢？
英文:
As the title says how does the map from org.springframework.data.domain.Page work?
As per the documentation, it suggests that you put a converter as a map parameter, and you get a new map with the converted contents. As per this interpretation, I wrote code to something as follows.
Page<T> results = getPagedResults();
return results.map(x -> {
x.setElement("some constant");
return x;
});
However the above did not work as expected. I got the Page with all the other values intact like count and so on, but the content was an empty list! I actually had to write code this way.
Page<T> results = getPagedResults();
return new Page<T>() {
@Override
public int getTotalPages() {
return results.getTotalPages();
}
...
@Override
public List<T> getContent() {
List<T> contents = result.getContent();
for (T content : contents) {
content.setElement("some constant");
}
return contents;
}
...
};
The second choice is verbose and seems to do redundant work. I would have expected the first piece of code to do the same, but it did not.
Am I reading the documentation wrong? And where would you use the map function of Page if it is not supposed to be used, the way I was using it?
答案1
得分: 0
如何尝试使用如下真实的转换器：
```java
Page<T> results = getPagedResults();
Page<T> convertedResults = results.map(new Converter<T, T>() {
@Override
public T convert(T page) {
Page page2 = new Page();
page2.setElement('某个常量');
//设置其他字段
return page2;
}
});
<details>
<summary>英文:</summary>
How about putting a real converter like below:
Page<T> results = getPagedResults();
Page<T> convertedResults = results.map(new Converter<T, T>() {
@Override
public T convert(T page) {
Page page2 = new Page();
page2.setElement('some constant');
//set other fields
return page2;
}
});
</details>
# 答案2
**得分**: 0
你可以像我们平常使用的方式一样使用 map：
```java
results.map(mapper::convert)
其中 convert 是 mapper 的方法，用于将数据库实体转换为 DTO 或其他任何对象。
英文:
You can use map the same way as we do:
results.map(mapper::convert)
where the convert is the method of mapper to convert database entity to DTO or any another object.
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