Power Bi查询到Web服务 - 错误：Expression.Error：我们无法将值转换为Record类型

Question

我有一个生成JSON的Web服务。我们对它进行jQuery REST调用并将数据绑定到Tables。

该服务是C＃WEBAPI，代码如下：

  data = serializer.Serialize(rows);
  return Request.CreateResponse(HttpStatusCode.OK, lstFilteredData, Configuration.Formatters.JsonFormatter);

它生成这样的JSON：

"[{\"School\":\"UM \",\"Students\":\"500\"},{\"School\":\"FIU \",\"Students\":\"700\"},{\"School\":\"UF \",\"Students\":\"600\"},{\"School\":\"GT \",\"Students\":\"300\"}]"

我们有jQuery REST成功使用这样的服务：

 $.ajax({
        url: 'https://myservices')),
        type: 'GET',
        dataType: 'json',
        cache: false,
        crossDomain: true,
        //async: false,
        success: function (data){  onQuerySucceededWeb(data,true,param);}
    }); 

我想使用Power Bi报告该数据。我的PowerBi查询脚本是：    让

Source = Json.Document(Web.Contents("https://mywebservices")),
  #"Converted to Table" = Record.ToTable(Source),
    #"Expanded Value" = Table.ExpandListColumn(#"Converted to Table", "Value"),
    #"Expanded Value1" = Table.ExpandRecordColumn(#"Expanded Value", "Value", {"School", "Students"}, {"Value.School", "Value.Students"})

in 
  #"Expanded Value1"

我收到此错误：

**Expression.Error: We cannot convert the value "[{"School":"UM      ..." to type Record.**
Details:
    Value=[{"School":"UM        ","Students":"500"},{"School":"FIU       ","Students":"700"},{"School":"UF        ","Students":"600"},{"School":"GT        ","Students":"300"}]
    Type=Type

Answer 1

Json.Document返回一个文本值，因为返回的JSON是一个字符串。如果删除引号，Json.Document应将其解析为对象列表。这应该有效：

let
    Source = Web.Contents("https://mywebservices")
    Custom1 = Text.Range(Source, 1, Text.Length(Source) - 2),
    Custom2 = Json.Document(Custom1),
    #"Converted to Table" = Table.FromList(Custom2, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Expanded Column1" = Table.ExpandRecordColumn(#"Converted to Table", "Column1", {"School", "Students"}, {"School", "Students"})
in
    #"Expanded Column1"`

如果网站返回空字符串，则会失败。

Answer 2

您的服务器上可能已损坏，因为您的JSON是对象的JSON字符串。如果服务器没有对JSON文本进行字符串化，那么你的M查询就会有效，即按字面意思生成这些字节：

[{"School":"UM ","Students":"500"},{"School":"FIU ","Students":"700"},{"School":"UF ","Students":"600"},{"School":"GT ","Students":"300"}]

如果您只想让M再次使用，可以对JSON进行双重解码：

= Json.Document(Json.Document(Web.Contents("https://mywebservices")))