一个思考这个问题的方法是看看构建CommentMultiTreeDatabaseModel
所需的数据。它需要一个CommentDatabaseModel
和一个CommentMultiTreeDatabaseModel
列表。因此我们需要编写以下两个函数:
let parseComment (input : JSON) : CommentDatabaseModel =
...
let parseTree (input : JSON) : CommentMultiTreeDatabaseModel =
...
但是等等,parseTree
函数就是我们现在要编写的!因此,我们不需要编写新函数,只需使用rec
关键字标记当前函数,并在需要时调用自身。
下面是一个简单的示例,展示了如何实现。需要注意的关键点是parseTree
通过递归调用自身来构建数据。我用简单的DU表示了JSON输入数据。类似于Chiron这样的库可以生成类似于此的内容。
请注意,此代码一次性解析所有JSON。此外,它不是尾递归,因此您需要小心树结构的深度。
[<RequireQualifiedAccess>]
type JSON =
| String of string
| Object of (string * JSON) list
| Array of JSON list
type public CommentDatabaseModel = {
commentId : string
userId : string
message : string
}
type public CommentMultiTreeDatabaseModel =
| CommentDatabaseModelNode of CommentDatabaseModel * list<CommentMultiTreeDatabaseModel>
let parseComment = function
| JSON.Object [ "commentId", JSON.String commentId; "userId", JSON.String userId; "message", JSON.String message ] ->
{
commentId = commentId
userId = userId
message = message
}
| _ -> failwith "Bad data"
let rec parseTree (input : JSON) : CommentMultiTreeDatabaseModel =
match input with
| JSON.Object [ "commentModel", commentModel; "forest", JSON.Array forest ] ->
CommentDatabaseModelNode (parseComment commentModel, List.map parseTree forest)
| _ -> failwith "Bad data"
let parse (input : JSON) : CommentMultiTreeDatabaseModel =
match input with
| JSON.Object [ "commentTree", commentTree ] ->
parseTree commentTree
| _ -> failwith "Bad data"
let comment text =
JSON.Object [
"commentId", JSON.String ""
"userId", JSON.String ""
"message", JSON.String text
]
let sampleData =
JSON.Object [
"commentTree", JSON.Object [
"commentModel", comment "one"
"forest", JSON.Array [
JSON.Object [
"commentModel", comment "two"
"forest", JSON.Array []
]
JSON.Object [
"commentModel", comment "three"
"forest", JSON.Array []
]
]
]
]
parse sampleData