jQuery submits post json data to webApi

When the page thinks about webApi post json data, it is found that webapi can not directly accept data in the way of json (note: I didn't find a good way to come to post json data); But it can be transmitted in the form of data structure;

As follows:

//js Code  
          var d = {
          Id: "1",
          Name: "name",
          Value: "OldValue", 7         };
        $.ajax({
          type: "post",
          url: url1,
          data: JSON.stringify({
            pConfig: d
          }),
          success:function(d){
          }
        });

public class Diff
  {
    public string Id { set; get; }
    public string Name { set; get; }
    public string Value { set; get; }
  }
 public Diff post([FromBody]Diff pConfig)
    {
      List<DiffConfig> s = pConfig;
      return s;
    }

There is no problem with code like this; The data of a standard structure is obtained.

But if you change to the following code, you will find that there is no data

//js Code  
         var d = [{
           Id: "1",
           Name: "name",
           Value: "Value",
         },{
           Id: "2",
           Name: "name2",
           Value: "Value2",
         }];
         $.ajax({
          type: "post",
          url: url1,
           data: JSON.stringify({
             pConfig: d
          }),
           success:function(d){
         }
        });

public List<Diff> post([FromBody]List<Diff> diff)
     {
       List<Diff> d = diff;
       return d;
     }

Such code will find that the data has not been transmitted, and it will be discovered later that there is a problem with the ajax transmission data type of the original jq; The default value of the transmitted data type contentType is "application/x-www-form-urlencoded". The default value is suitable for most cases. However, it can't adapt to the value of this transmission. If contentType: 'application/json' is set to 1, ok can be achieved; There is no problem in data transmission at all;

$.ajax({
      type: "post",
      dataType: 'json',
      url: url,
      contentType: 'application/json',
      data: JSON.stringify(d),
      success: function (d) {
       
      }
    });