Java Spring Data JPA Distinct - 从单列返回结果
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Spring Data JPA Distinct - Return results from a single column
提问by Rasmus Sj?rslev
I have some data that contains a STATEfield (String/Text) that defines what state a given request is currently in (e.g. pending, approved denied etc.) and to get all the unique values from that column I can run the following TSQL query
我有一些数据包含一个STATE字段（字符串/文本），该字段定义了给定请求当前处于什么状态（例如，待处理、已批准被拒绝等）并从该列中获取所有唯一值，我可以运行以下 TSQL 查询
SELECT DISTINCT STATE FROM CALLOUT_REQUEST
SELECT DISTINCT STATE FROM CALLOUT_REQUEST
where CALLOUT_REQUESTis my table name and STATEbeing the field which returns something like:
CALLOUT_REQUEST我的表名在哪里，是STATE返回如下内容的字段：
STATE
状态
- approved
- denied
- pending
- ...
- 得到正式认可的
- 拒绝
- 待办的
- ...
However I don't understand how I would turn that into a query in my repository as it seems I need a "by" statement or some other filter mechanism which i can get the STATEbased on?
但是我不明白如何将其转换为我的存储库中的查询，因为似乎我需要一个“by”语句或其他一些过滤机制，我可以获得STATE基于？
What I am looking to return - as shown in the raw TSQL query above - is some kind of List or Array object which contains all the unique/distinct values in all of the STATEfields.
我希望返回的 - 如上面的原始 TSQL 查询所示 - 是某种 List 或 Array 对象，其中包含所有STATE字段中的所有唯一/不同值。
So in pseudo code i think i am looking for something like this:
所以在伪代码中，我想我正在寻找这样的东西：
String[] states = repository.findDisinctState();
String[] states = repository.findDisinctState();
where findDistinctState()would then return an array of sorts.
findDistinctState()然后where会返回一个数组。
Hope that makes sense - I am very new to Java and Spring in general so I think I am missing some conceptual knowledge to utilise the above.
希望这是有道理的 - 总的来说，我对 Java 和 Spring 非常陌生，所以我认为我缺少一些概念性知识来利用上述内容。
UPDATE:
更新：
The 'state' concept is closed so i could implement that as an enum - only problem is i dont know how to do that :) Ill look into how i can do that as i think it fits perfectly with what i am trying to achieve.
“状态”概念已关闭，因此我可以将其实现为枚举 - 唯一的问题是我不知道如何做到这一点:) 我会研究如何做到这一点，因为我认为它完全符合我想要实现的目标。
The List i get from the query provided is intended to be used to get a count of all the occurrences. I had this code before to get a total count for each of the 'states':
我从提供的查询中获得的列表旨在用于获取所有出现次数的计数。我之前有这个代码来获得每个“状态”的总数：
Map stats = new HashMap();
String[] states = {"approved", "denied", "pending", "deactivated"};
for (int i = 0; i < states.length; i++) {
stats.put(states[i], repository.countByState(states[i]));
}
Am i correct in understanding that the states Arraythat i have in the above code snippet could be turned into an enum and then i dont even need the custom @Queryanymore?
我是否正确理解Array我在上述代码片段中的状态可以变成枚举，然后我什至@Query不再需要自定义？
采纳答案by Luís Soares
If that stateconcept is closed and you know it's a possible set of values, it should be an enum.
如果该state概念是封闭的并且您知道它是一组可能的值，则它应该是一个枚举。
After that you can create queriesthat you invoke like:
repository.findByState(State.APPROVED)
If you can't create an enum, you need a separate method to get the distinct values, which can't be provided by JPA, because you need an list of strings and not a list of CalloutRequests.
Then you need to specify a query manually like:
如果无法创建枚举，则需要一个单独的方法来获取不同的值，而 JPA 无法提供这些值，因为您需要的是字符串列表而不是CalloutRequests列表。然后你需要手动指定一个查询，如：
@Query("SELECT DISTINCT State FROM CALLOUT_REQUEST")
List<String> findDistinctStates();
回答by meskobalazs
You can use a JPQL query for this, with the @org.springframework.data.jpa.repository.Queryannotation:
您可以为此使用 JPQL 查询，并带有@org.springframework.data.jpa.repository.Query注释：
@Query("select distinct state from CalloutRequest")
List<String> findDistinctStates();
