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

I have a web service that produces JSON. We make jQuery REST calls to it and bind the data to Tables.

The service is C# WEBAPI with code like this:

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

It produces JSON that like this:

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

We have jQuery REST that successfully consumes the service like this:

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

I'm tring to report on that data using Power Bi. My PowerBi Query script is: let

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"

I'm getting this Error:

**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 is returning a text value because the JSON being returned is a string. If you remove the quotes, Json.Document should parse it as a list of objects. This should work:

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"`

This would fail if the web site ever returned an empty string.

Answer 2

Something might have broken on your server, because your JSON is a JSON string of an object. Your M query would have worked if the server hadn't stringified the JSON text, ie produced literally these bytes:

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

If you just want to get your M to work again, you can double-decode the JSON:

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