ModelState not updating when using JsonPatchDocument.ApplyTo<T>(T, ModelStateDictionary)

[TheWillieWonkaOfCode]

I was playing around with a REST service in ASP.NET Core MVC and found this issue.

Here is my model:

    public class Test
    {
        public int Id { get; set; }

        [Required]
        [StringLength(10, MinimumLength = 1)]
        public string FirstName { get; set; }

        [Required]
        [StringLength(10, MinimumLength = 1)]
        public string LastName { get; set; }

        public Test Copy()
        {
            Test newTest = new Test()
            {
                Id = this.Id,
                FirstName = FirstName,
                LastName = this.LastName
            };

            return newTest;
        }
    }

Here is my POST:

        [HttpPost]
        public IActionResult Create([FromBody] Test item)
        {
            if (item == null) return BadRequest();
            if (!ModelState.IsValid) return BadRequest();

            TestItems.Add(item);

            return CreatedAtRoute("GetTest", new { id = item.Id }, item);
        }

The validation fails correctly based on the attributes on the model.

Here is my PATCH (I have put comments around the issue):

       [HttpPatch("{id}")]
       public IActionResult Patch(string id, [FromBody] JsonPatchDocument<Test> patch)
       {
           int theId;
           if (!int.TryParse(id, out theId)) return BadRequest();
           if (patch == null) return BadRequest();

           Test item = TestItems.GetById(theId);
           if (item == null) return NotFound();

           // This is documented that it's supposed to update the ModelState, but it doesn't appear to do that
           // and the model is always valid even if the updated values are not valid. The ModelState object
           // only contains the id that was passed, it is not validating the parts in the patch instance. V1.1
           // is not GA yet, so it may just be unfinished code.
           patch.ApplyTo(item, ModelState);
           // I shouldn't need to make this call, but the ModelState isn't updated by the ApplyTo call.
           // This correctly updates the ModelState with the errors.
           TryValidateModel(item);
           if (!ModelState.IsValid) return BadRequest();

           TestItems.Update(item);
           return new NoContentResult();
       }

I tried sending a replace for the FirstName to an empty string, and to a string that was too long. In both cases, the ModelState was unchanged after the call to ApplyTo. I added the call to TryValidateModel and that caused the ModelState to then be updated with errors.

[Tratcher]

@rynowak ?

[chriskooken]

I am having this same problem. Any updates on this?

[Eilon]

This issue was moved to aspnet/Mvc#7598

[akalcik]

I think this is still issue which leads to inconsistencies. I opened new feature request on this #7158