InvalidOperationException is thrown while patching elements in array

[anaruzhnii]

Environment

• Nuget Package: JsonPatch.Net
• Nuget Version: 2.0.4
• OS: Windows 11 Pro
• .Net Target: .NET 5, 6, 7

Describe the bug
InvalidOperationException is thrown when I try to patch JSON object from a JSON array.
Exception message: The node already has a parent.
See call stack below.

To Reproduce

• Parse JSON array
• Pick one object and try to patch it
• Get an error

Code to reproduce the problem

using System;
using System.Linq;
using System.Text.Json;
using System.Text.Json.Nodes;
using Json.More;
using Json.Patch;
using Json.Pointer;

const string mask = "*****";
var maskJson = JsonValue.Create(mask);

var pathsToPatch = new[] { "/first_name", "/last_name" };

var patchOperations = pathsToPatch.Select(path => PatchOperation.Replace(JsonPointer.Parse(path), maskJson));
var patchConfig = new JsonPatch(patchOperations);

const string singleObjectJson = "{" +
    "\"_id\":\"640729d45434f90313d25c78\"," +
    "\"guid\":\"f2e2767c-03e0-4862-addc-7d46c55efb33\"," +
    "\"first_name\":\"Kathrine\"," +
    "\"last_name\":\"Pate\"" +
    "}";

var singleObject = JsonDocument.Parse(singleObjectJson).RootElement;
var patchedSingleObject = patchConfig.Apply(singleObject.AsNode()).Result;
Console.WriteLine(JsonSerializer.Serialize(patchedSingleObject));

const string arrayObjectJson = "[" +
    "{" +
    "\"_id\":\"640729d45434f90313d25c78\"," +
    "\"guid\":\"f2e2767c-03e0-4862-addc-7d46c55efb33\"," +
    "\"first_name\":\"Kathrine\"," +
    "\"last_name\":\"Pate\"" +
    "}," +
    "{\"_id\":\"640729d45b5824ffcabc30a5\"," +
    "\"guid\":\"73193eda-074b-4f31-9f09-507a008ccb75\"," +
    "\"first_name\":\"Rivers\"," +
    "\"last_name\":\"Smith\"" +
    "}" +
    "]";

var arrayObject = JsonDocument.Parse(arrayObjectJson).RootElement;

// Way 1: patch whole array
var patchedArray = patchConfig.Apply(arrayObject.AsNode()).Result;  // <- does nothing

var jsonArray = arrayObject.AsNode().AsArray();

// Way 2: just patch every element
foreach (var element in jsonArray)
{
    var patchedNode = patchConfig.Apply(element).Result;            // <-  throws an error
}

// Way 3: remove from initial array and then patch
for (int currentIndex = jsonArray.Count - 1; currentIndex >= 0; currentIndex--)
{
    var nodeToPatch = jsonArray[currentIndex];
    jsonArray.RemoveAt(currentIndex);

    var patchedNode = patchConfig.Apply(nodeToPatch).Result;        // <-  throws an error
}

Expected behavior
JSON object is patched successfully.

Additional context

• Patching of a single object works fine
• Patching of array as a whole does nothing (see Way 1 in code above)
• It looks like removing the object from JSON array resets its parent (see Way 3), but it doesn't work either.

Call stack

   System.InvalidOperationException: The node already has a parent.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_NodeAlreadyHasParent()
   at System.Text.Json.Nodes.JsonNode.AssignParent(JsonNode parent)
   at System.Text.Json.Nodes.JsonObject.<>c__DisplayClass9_0.<SetItem>b__0()
   at System.Text.Json.JsonPropertyDictionary`1.SetValue(String propertyName, T value, Action assignParent)
   at System.Text.Json.Nodes.JsonObject.SetItem(String propertyName, JsonNode value)
   at System.Text.Json.Nodes.JsonNode.set_Item(String propertyName, JsonNode value)
   at Json.Patch.ReplaceOperationHandler.Process(PatchContext context, PatchOperation operation)
   at Json.Patch.PatchOperation.Handle(PatchContext context)
   at Json.Patch.JsonPatch.Apply(JsonNode source)
   at Program.<Main>$(String[] args) in C:\upteam\Experiments\JsonPatchNetBug\Program.cs:line 48

[gregsdennis]

Thanks for reporting this. Yeah, it seems I have several places across the libs where I just assign a pre-existing node instead of copying it.

This should be a simple fix.

[gregsdennis]

So the first case, where it does nothing, is correct. It should do nothing because the locations indicated by the patch don't exist.

The patch is

[
  {"op":"replace","path":"/first_name","value":"*****"},
  {"op":"replace","path":"/last_name","value":"*****"}
]

The data is

[
  {"_id":"640729d45434f90313d25c78","guid":"f2e2767c-03e0-4862-addc-7d46c55efb33","first_name":"Kathrine","last_name":"Pate"},
  {"_id":"640729d45b5824ffcabc30a5","guid":"73193eda-074b-4f31-9f09-507a008ccb75","first_name":"Rivers","last_name":"Smith"}
]

/first_name and /last_name aren't valid locations within the data, so it does nothing. You should be able to confirm this on other JSON Patch sites.

As far as I'm aware, there's not a way to apply a single patch to all elements in an array at once like this. Mainly this is due to JSON Patch using JsonPointer which can only indicate a single location within a JSON structure. You'd need to indicate multiple locations.

[gregsdennis]

Lastly, just a suggestion.

Instead of

var singleObject = JsonDocument.Parse(singleObjectJson).RootElement;
var patchedSingleObject = patchConfig.Apply(singleObject.AsNode()).Result;

Just use JsonNode.Parse():

var singleObject = JsonNode.Parse(singleObjectJson);
var patchedSingleObject = patchConfig.Apply(singleObject).Result;