如何在将linq to-json查询从c＃转换为vb.net之后解决无效的castection

Question

我正在尝试使用此C＃答案中的代码转换为将嵌套的JSON转换为CSV ，但我的项目是vb.net。我尝试了很少的在线转换器，但没有成功。C＃版本效果很好，但VB.NET版本抛出了InvalidCastException。有什么问题？

我的JSON：

  {
  "Response": [
    [
      {
        "id": 136662306,
        "symbol": "aaa",
        "status": "ACTIVE",
        "base": "731.07686321",
        "amount": "6.95345994",
        "timestamp": "1524781083.0",
        "swap": "0.0",
        "pl": "5127.4352653395923394"
      },
      {
        "id": 137733525,
        "symbol": "bbb",
        "status": "ACTIVE",
        "base": "636.75093128",
        "amount": "1.1",
        "timestamp": "1531902193.0",
        "swap": "0.0",
        "pl": "687.800226608"
      }
    ]
  ]
}

我的C＃版本

JObject obj = JObject.Parse(json);
// Collect column titles: all property names whose values are of type JValue, distinct, in order of encountering them.
var values = obj.DescendantsAndSelf()
    .OfType<JProperty>()
    .Where(p => p.Value is JValue)
    .GroupBy(p => p.Name)
    .ToList();
var columns = values.Select(g => g.Key).ToArray();
// Filter JObjects that have child objects that have values.
var parentsWithChildren = values.SelectMany(g => g).SelectMany(v => v.AncestorsAndSelf().OfType<JObject>().Skip(1)).ToHashSet();
// Collect all data rows: for every object, go through the column titles and get the value of that property in the closest ancestor or self that has a value of that name.
var rows = obj
    .DescendantsAndSelf()
    .OfType<JObject>()
    .Where(o => o.PropertyValues().OfType<JValue>().Any())
    .Where(o => o == obj || !parentsWithChildren.Contains(o)) // Show a row for the root object + objects that have no children.
    .Select(o => columns.Select(c => o.AncestorsAndSelf()
        .OfType<JObject>()
        .Select(parent => parent[c])
        .Where(v => v is JValue)
        .Select(v => (string)v)
        .FirstOrDefault())
        .Reverse() // Trim trailing nulls
        .SkipWhile(s => s == null)
        .Reverse());
// Convert to CSV
var csvRows = new[] { columns }.Concat(rows).Select(r => string.Join(",", r));
var csv = string.Join("n", csvRows);

我的vb.net版本给出以下例外：

system.invalidcastException：'无法施放类型的对象'WhereselectEnumoserator`2

Dim obj As JObject = Nothing
obj = JObject.Parse(json)
Dim values = obj.DescendantsAndSelf().
                 OfType(Of JProperty)().
                 Where(Function(p) TypeOf p.Value Is JValue).
                 GroupBy(Function(p) p.Name).ToList()
Dim columns = values.[Select](Function(g) g.Key).ToArray()
Dim parentsWithChildren = values.SelectMany(Function(g) g).
                                            SelectMany(Function(v) v.AncestorsAndSelf().
                                            OfType(Of JObject)().Skip(1)).ToHashSet()
Dim rows = obj.DescendantsAndSelf().
               OfType(Of JObject)().
               Where(Function(o) o.PropertyValues().
               OfType(Of JValue)().Any()).
               Where(Function(o) o = obj OrElse Not parentsWithChildren.Contains(o)).
               [Select](Function(o) columns.[Select](Function(c) o.AncestorsAndSelf().
                    OfType(Of JObject)().
                    [Select](Function(parent) parent(c)).
                    Where(Function(v) TypeOf v Is JValue).
                    [Select](Function(v) CStr(v)).
                    FirstOrDefault()).
                    Reverse().
                    SkipWhile(Function(s) s Is Nothing).
                    Reverse())
Dim csvRows = {columns}.Concat(rows).[Select](Function(r) String.Join(",", r))   ' HERE IS WHERE THE EXCEPTION OCCURS
Dim csv = String.Join(vbLf, csvRows)

例外

{"Unable to cast object of type 'WhereSelectEnumerableIterator`2[Newtonsoft.Json.Linq.JObject,System.Collections.Generic.IEnumerable`1[System.String]]' to type 'System.Collections.Generic.IEnumerable`1[System.String[]]'."}

Answer 1

为了使{columns}.Concat(rows)工作，您似乎需要向AsEnumerable()添加一个明确调用，以确保正确推断Enumerable.Concat(IEnumerable<TSource>, IEnumerable<TSource>)的TSource类型：

Dim csvRows = { columns.AsEnumerable() }.Concat(rows) _
                .Select(Function(r) String.Join(",", r))

修复了这里的小提琴＃1。

a DirectCast({columns}, IEnumerable(Of IEnumerable(Of String)))似乎也起作用，如Ahmed Abdelhameed的评论中所述：

Dim csvRows = DirectCast({columns}, IEnumerable(Of IEnumerable(Of String))).Concat(rows) _
                .Select(Function(r) String.Join(",", r))

修复了这里的小提琴＃2。

在不利用推断的情况下明确调用Enumerable.Concat(Of IEnumerable(Of String))，也有效：

Dim csvRows = Enumerable.Concat(Of IEnumerable(Of String))({columns}, rows) _
                .Select(Function(r) String.Join(",", r))

修复了这里的小提琴＃3。

因此，您的整个代码应该看起来像：

Dim obj As JObject = JObject.Parse(json)
Dim values = obj.DescendantsAndSelf().OfType(Of JProperty)().Where(Function(p) TypeOf p.Value Is JValue).GroupBy(Function(p) p.Name).ToList()
Dim columns = values.[Select](Function(g) g.Key).ToArray()
Dim parentsWithChildren = values.SelectMany(Function(g) g).SelectMany(Function(v) v.AncestorsAndSelf().OfType(Of JObject)().Skip(1)).ToHashSet()
Dim rows = obj.DescendantsAndSelf() _
                    .OfType(Of JObject)() _
                    .Where(Function(o) o.PropertyValues().OfType(Of JValue)().Any()) _
                    .Where(Function(o) o.Equals(obj) OrElse Not parentsWithChildren.Contains(o)) _
                    .Select(Function(o) columns.Select(Function(c) _
                                                    o.AncestorsAndSelf() _
                                                    .OfType(Of JObject)() _
                                                    .Select(Function(parent) parent(c)) _
                                                    .OfType(Of JValue)() _
                                                    .Select(Function(v) CStr(v)) _
                                                    .FirstOrDefault()) _
                                                .Reverse() _
                                                .SkipWhile(Function(s) s Is Nothing) _
                                                .Reverse())
Dim csvRows =  { columns.AsEnumerable() }.Concat(rows) _
                .Select(Function(r) String.Join(",", r)) 
Dim csv = String.Join(vbLf, csvRows)