使play-json对于Option [T]类型的空字符串读取为None [英] make play-json read the empty string as None for a type of Option[T]
问题描述
我正在尝试使用play-json从GitHub API解析json，并在Pull Requests上遇到merge_commit_sha字段的问题(顺便说一句，我知道此字段已弃用，但不想讨论在这个解析问题中！).不幸的是，在某些情况下，merge_commit_sha字段作为空字符串返回:
I'm attempting to parse json from the GitHub API with play-json, and encountering a problem with the merge_commit_sha field on Pull Requests (incidentally, I know this field is deprecated, but don't want to discuss that in this parsing problem!). Unfortunately merge_commit_sha field comes back as the empty string in some cases:
"merge_commit_sha": ""
这是我有一个
I have an implicit Format[ObjectId], which does not tolerate the empty string, because that's not a valid value for a Git hash id. I'm also using a play-json macro-generated Read[PullRequest], which I'd like to keep on using, in preference to individually declaring reads for every single field on pull requests.
正如我已经声明该字段为Option一样，我希望将"merge_commit_sha": ""读取为值None，但这不是当前发生的情况-存在字符串，因此Format[ObjectId]被调用，并返回JsFailure.
As I've declared the field to be an Option, I'd like "merge_commit_sha": "" to be read as the value None, but this is not what currently happens - a string is present, so the Format[ObjectId] is invoked, and returns a JsFailure.
我尝试过的一件事是声明具有所需行为的隐式Format[Option[ObjectId]]，但似乎并没有被宏生成的Read[PullRequest]所使用.
One thing I tried was declaring an implicit Format[Option[ObjectId]] with the required behaviour, but it didn't seem to get used by the macro-generated Read[PullRequest].
推荐答案
您可以定义自定义使用Json.format[MyType]使用Scala宏. 您也许可以加入其中.尽管为这个case class'扩展'宏似乎是错误的.
Using Json.format[MyType] uses a Scala macro. You may be able to hook into that. Although, 'extending' a macro for this one case class just seems wrong.
自定义读取和写入可能有点样板式"并且很无聊，但是它们有其优势.
Custom Reads and Writes might be a little 'boilerplate-like' and boring, but they have their upsides.
例如，如果您的json上有一堆新字段，则在将其验证或转换为case class时不会得到JsError.您只需从JSON中获取所需的内容并创建对象.它还可以将您的内部模型与您所消费的内容区分开来，在某些情况下，这是首选.
For example if your json has a bunch of new fields on it, you wont get a JsError when validating or transforming it to a case class. You only take what you need from the JSON and create objects. It also allows for a separation between your internal model and what you're consuming, which in some cases is preferred.
我希望这会有所帮助，
Rhys
编辑
Rhys
EDIT
使用其他一些JSON库之后，我可能已经找到了您想要的东西. 我知道这个问题是在播放JSON之后专门问的.
After using some other JSON libs I may have found what you are looking for. I know the question was asking specifically after Play JSON.
如果您能够摆脱Play JSON，请查看 spray-json-shapeless 特别是JsNullBehaviour和JsNullNotNone
If you're able to move away from Play JSON, Look at spray-json-shapeless specifically JsNullBehaviour and JsNullNotNone REF.
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