json - Play JSON : reading optional nested properties

Question

我有以下案例类和 JSON 组合器:

case class Commit(
    sha: String,
    username: String,
    message: String
)

object Commit {
    implicit val format = Json.format[Commit]
}

case class Build(
    projectName: String,
    parentNumber: String,
    commits: List[Commit]
)

val buildReads: Reads[Build] =
    for {
        projectName <- (__ \ "buildType" \ "projectName").read[String]
        name <- (__ \ "buildType" \ "name").read[String]
        parentNumber <- ((__ \ "artifact-dependencies" \ "build")(0) \ "number").read[String]
        changes <- (__ \ "changes" \ "change").read[List[Map[String, String]]]
    } yield {
        val commits = for {
            change <- changes
            sha <- change.get("version")
            username <- change.get("username")
            comment <- change.get("comment")
        } yield Commit(sha, username, comment)
        Build(s"$projectName::$name", parentNumber, commits)
    }

我的 Build 的 JSON 读取组合器将处理传入的 JSON，例如:

{
    "buildType": {
        "projectName": "foo",
        "name": "bar"
    },
    "artifact-dependencies": {
        "build": [{
            "number": "1"
        }]
    },
    "changes": {
        "change": [{
            "verison": "1",
            "username": "bob",
            "comment": "foo"
        }]
    }
}

但是，如果缺少artifact-dependencies，它就会崩溃。我希望这是可选的。

我应该使用 readNullable 吗？我曾尝试这样做，但失败了，因为它是一个嵌套属性。

这看起来实用吗，还是我在滥用 JSON 组合器将我的 JSON 解析为案例类？

Answer 1

目前未使用其伴随对象中的 Format[Commit]。我们没有理由不能为此使用简单的组合器并分离逻辑。

case class Commit(sha: String, username: String, message: String)

object Commit {

    implicit val reads: Reads[Commit] = (
        (__ \ "version").read[String] and 
        (__ \ "username").read[String] and 
        (__ \ "comment").read[String]
    )(Commit.apply _)

}

然后，如果 "artifact-dependencies" 可以丢失，我们应该在 Build 中将 parentNumber 设为 Option[String] .

 case class Build(projectName: String, parentNumber: Option[String], commits: List[Commit])

我将合并项目名称的 Reads 拆分为一个单独的，以使 Reads[Build] 看起来更干净一些。

val nameReads: Reads[String] = for {
    projectName <- (__ \ "projectName").read[String]
    name <- (__ \ "name").read[String]
} yield s"$projectName::$name"

然后，当缺少"artifact-dependencies"时，我们可以使用orElse和Reads.pure(None)来填充它当整个分支(或子分支)不存在时使用 None。在这种情况下，这比映射每个步骤要简单。

implicit val buildReads: Reads[Build] = (
    (__ \ "buildType").read[String](nameReads) and
    ((__ \ "artifact-dependencies" \ "build")(0) \ "number").readNullable[String].orElse(Reads.pure(None)) and
    (__ \ "changes" \ "change").read[List[Commit]]
)(Build.apply _)

val js2 = Json.parse("""
{
    "buildType": {
        "projectName": "foo",
        "name": "bar"
    },
    "changes": {
        "change": [{
            "version": "1",
            "username": "bob",
            "comment": "foo"
        }]
    }
}
""")

scala> js2.validate[Build]
res6: play.api.libs.json.JsResult[Build] = JsSuccess(Build(foo::bar,None,List(Commit(1,bob,foo))),)