修改 Spring Data REST 投影后面生成的 SQL 查询-Java问题

Modify SQL query generated behind Spring Data REST projections(修改 Spring Data REST 投影后面生成的 SQL 查询)

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问题描述

如何在 SELECT 中只保留 Spring Data Rest Projections 所需的列?

EDIT : How to Keep only needed columns in SELECT for Spring Data Rest Projections?

Spring Data Rest Projections 非常适合获取生成的链接的列子集，但在后面生成的查询仍然包含所有列.

Spring Data Rest Projections are good for getting a subset of columns for links which are generated, but the Query that gets generated in behind still has all columns in it.

在 SQL 查询也只有 SELECT 中的那些列在 Projection 中的情况下，如何创建 Projections

How can Projections be created where also SQL queries have only those columns in SELECT which are in Projection

推荐答案

我不知道为什么文档中缺少它，但是这个 spring 示例(来自 spring)显示您可以使用投影作为 @ 的返回类型询问.所以你可以这样做:

I don't know why it's missing from the docs, but this spring sample (from spring) shows that you can use projections as the return type for a @Query. So you can do:

public interface ActionId {
    String getId(); 
}

@Query("select a.id as id from Action a where a.type = :type")
public List<ActionId> findByType(@Param("type") String type);

现在不必使用构造函数表达式，您可以更简洁地选择所需的列，然后返回一个对象.我希望可以将投影应用于域对象本身，因此您仍然可以仅返回 id 字段的Action"，但现在看来不可能-

Now instead of having to use constructor expressions, you can more succinctly just select the columns you want, and return an object. I wish that projections could be applied to the domain object itself, so you could still return an "Action" with just the id field, but that doesn't look possible now-

参考:https://github.com/spring-projects/spring-data-examples/blob/master/jpa/example/src/main/java/example/springdata/jpa/projections/CustomerRepository.java

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