成功反序列化 JSON 后无法访问属性

Question

在反序列化某些JSON并尝试访问root.items后，我收到以下错误：

 root.items.Count |> should equal 2

System.NullReferenceException： 'Object reference 未设置为 对象的实例。

root.items@为空。

JSON 如下所示：

{
    "items": [
        {
            "snippet": {
                "title": "Nikeza: F# Backwards Pipe Operator",
                "tags": [
                    "Elm",
                    "F#",
                    "Giraffe",
                    "Functional Programming",
                    "Software Development"
                ]
            }
        },
        {
            "snippet": {
                "title": "Giraffe: VS Code bug that doesn't show up in VS 20017 (3)",
                "tags": [
                    "Hangouts On Air",
                ]
            }
        },
        {
            "snippet": {
                "title": "Software Craftsmanship Conference - London",
                "tags": [
                    "Programming",
                    "Software Development",
                ]
            }
        }
    ]
}

这是我的代码：

[<CLIMutable>]
type Snippet =    { title: string; tags: Collections.Generic.List<String> }
[<CLIMutable>]
type Item =       { snippet : Snippet }
[<CLIMutable>]
type Response =   { items : Collections.Generic.List<Item> }
[<Test>]
let ``Apply tags to videos`` () =
    let  delimitedIds = ["id1";"id2";"id3"] |> String.concat ","
    let  url = String.Format(requestTagsUrl, apiKey, delimitedIds)
    let response = httpClient.GetAsync(url) |> Async.AwaitTask |> Async.RunSynchronously
    if response.IsSuccessStatusCode
        then let root = response.Content.ReadAsAsync<Response>() |> Async.AwaitTask |> Async.RunSynchronously
             root.items.Count |> should equal 2
        else Assert.Fail()

Answer 1

我刚刚为它写了一个测试，我可以确认它的反序列化部分是正确的。检查请求是否正确返回响应。

open System
open Expecto
let json = 
    """
    {
        "items": [
            {
                "snippet": {
                    "title": "Nikeza: F# Backwards Pipe Operator",
                    "tags": [
                        "Elm",
                        "F#",
                        "Giraffe",
                        "Functional Programming",
                        "Software Development"
                    ]
                }
            },
            {
                "snippet": {
                    "title": "Giraffe: VS Code bug that doesn't show up in VS 20017 (3)",
                    "tags": [
                        "Hangouts On Air",
                    ]
                }
            },
            {
                "snippet": {
                    "title": "Software Craftsmanship Conference - London",
                    "tags": [
                        "Programming",
                        "Software Development",
                    ]
                }
            }
        ]
    }
    """
[<CLIMutable>]
type Snippet =    { title: string; tags: Collections.Generic.List<String> }
[<CLIMutable>]
type Item =       { snippet : Snippet }
[<CLIMutable>]
type Response =   { items : Collections.Generic.List<Item> }
[<Tests>]
let tests =
    testList "Test" [
        test "Testing deserialization" {
            let result : Response = Json.deserialize json
            Expect.equal result.items.Count 3 "Should have 3 items"
        }
    ]                

Answer 2

以下内容对我有用：

总之，我不得不使用以下方法检索实际的 json 字符串：

json = response.Content.ReadAsStringAsync() |> Async.AwaitTask |> Async.RunSynchronously

之后，我使用了JsonConvert.DeserializeObject：

JsonConvert.DeserializeObject<Response>(json)

附录：

if response.IsSuccessStatusCode
    then let json = response.Content.ReadAsStringAsync() |> Async.AwaitTask |> Async.RunSynchronously
         let result = JsonConvert.DeserializeObject<Response>(json);