用列表对JSON对象进行比较会返回对象而不是数组

Question

I'm trying to compare two C# objects by converting them to JSON and then making a diff. It works fine for all primitives but I don't understand why when I change items in a list that had items the comparison is retuning an object instead of an array.

I'm going to list 3 cases, the first 2 go by as expected:

Case 1 - previous list was empty and one item was added later

var company = new Company(15)
{
    Name = "Sega"
};
var previousCat = new Category(1)
{
    Name = "Cat X",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = company
    },
    Companies = new List<Company>()
};
var currentCat = new Category(1)
{
    Name = "Cat XYZ",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = company
    },
    Companies = new List<Company> { company }
};

Result as expected*

// New Value:

[
  {
    "Name": "Sega",
    "Categories": null,
    "Id": 15
  }
]

// Old value:

[]

Case 2 - previous list had one item that was later removed

var company = new Company(15)
{
    Name = "Sega"
};
var previousCat = new Category(1)
{
    Name = "Cat X",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = company
    },
    Companies = new List<Company>
    {
        company
    }
};
var currentCat = new Category(1)
{
    Name = "Cat XYZ",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = company
    },
    Companies = new List<Company>()
};

Result as expected*

// New value:

[]

// Old Value:

[
  {
    "Name": "Sega",
    "Categories": null,
    "Id": 15
  }
]

Case 3 - both lists have items

var sega = new Company(15)
{
    Name = "Sega"
};
var sony = new Company(30)
{
    Name = "Sony"
};
var nintendo = new Company(45)
{
    Name = "Nintendo"
};
var microsoft = new Company(60)
{
    Name = "Microsoft"
};
var previousCat = new Category(1)
{
    Name = "Cat X",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = sega
    },
    Companies = new List<Company>
    {
        sega,
        nintendo
    }
};
var currentCat = new Category(1)
{
    Name = "Cat XYZ",
    Department = new Department(100)
    {
        Name = "Department 100",
        Company = sega
    },
    Companies = new List<Company>
    {
        nintendo,
        sony,
        microsoft
    }
};

Result NOT as expected*

// New value:

{
  "0": {
    "Name": "Nintendo",
    "Id": 45
  },
  "1": {
    "Name": "Sony",
    "Id": 30
  },
  "2": {
    "Name": "Microsoft",
    "Categories": null,
    "Id": 60
  },
  "@@ Count": 3
}

// Old value:

{
  "0": {
    "Name": "Sega",
    "Id": 15
  },
  "1": {
    "Name": "Nintendo",
    "Id": 45
  },
  "@@ Count": 2
}

As you can see the third result returns an object, not an array. Why is that?

I'm using this class:

https://github.com/khalidsalomao/SimpleHelpers.Net/blob/master/SimpleHelpers/ObjectDiffPatch.cs

This way:

var diff = ObjectDiffPatch.GenerateDiff(Previous,Current);

Answer 1

That's probably because of the way the code you linked ( ObjectDiffPatch ) builds up the array diff object. This is the relevant part, as I recreated it in LINQPad :

I added this as an image because that tooltip is important here. But let's start at the top:

If one of the arrays is empty, it properly keeps the original structure: grabs the two arrays (one of which is empty), and adds them under the field name "Companies".

If, however, neither are empty, then it starts comparing their contents, piece by piece. And when a difference is found, the code adds it to the diff object using AddNewValuesToken , which expects a field name as its third parameter, but here we don't have a field name, just an array index .

Now, the code "solves" this by converting the array index to string , and treating it as a field name. No wonder that the resulting JObject will treat it that way too – this is why you see an object in the output, where what used to be array indices, become fields.