ASP.NET Core 3.1 OData PageResult 序列化

Question

The PageResult response is missing the nextPageLink and count values when being serialized through System.Text.Json (ASP.NET Core 3 default) for the following result:

[ApiController]
[Route("api/[controller]")]
public class ValuesController : ControllerBase
{
  [HttpGet]
  public IActionResult Get()
  {
    var items = new List<string> { "value" };

    var pageResult = new Microsoft.AspNet.OData.PageResult<string>(items, new Uri("http://localhost/foo"), items.Count);

    return Ok(pageResult);
  }
}

However when I use the Newtonsoft.Json formatter , the result is correct:

public void ConfigureServices(IServiceCollection services)
{
  services.AddControllers().AddNewtonsoftJson();
}

Result with System.Text.Json :

[
    "value"
]

Result with Newtonsoft.Json :

{
    "items": [
        "value"
    ],
    "nextPageLink": "http://localhost/foo",
    "count": 1
}

Any idea what the reason is for this behaviour?

Answer 1

On re-reading the question, this doesn't directly answer why the OP's question of why one formatter does and another does not cause the correct output, but may provide some places for the OP to start looking...

I have also seen interesting behaviour when using OData and Asp.Net Core, it's very difficult to decipher from the online documentation what you should do these days, as most of the docs seem to out of date or for earlier versions of OData. For example, you'll see some references to GetInlineCount() in some documtation, but it appears to have been removed from the API.

For your query, I think you have two options Firstly, change your return type to be IQueryable then specify the attribute [EnableQuery(PageSize=10)] .

Alternatively, keeping what what you have, and using the PageResult object:

return new PageResult<object>(listOfObjects as IEnumerable<object>, Request.GetNextPageLink(5), Request.ODataFeature().TotalCount);

You can solve the Request.ODataFeature().TotalCount not returning a value by setting the Request.ODataFeature().TotalCountFunc function as follows...

Request.ODataFeature().TotalCountFunc = () => listOfobjects.Count();

Answer 2

[ApiController]
[Route("api/[controller]")]
public class ValuesController : ODataController
{
  [HttpGet]
  [EnableQuery(PageSize=5)]
  public IActionResult Get()
  {
    var items = new List<string> { "value1","value2","value3","value4","value5"  };
 
    return Ok(items);
  }
}

Extend your controller with ODataController instead of ControllerBase . [EnableQuery] attribute needs to be added to the method. You can define a PageSize if you're doing server side paging.