.NET Core 3.1 - Ajax OnGet and return objects using NEW System.Text.Json - asp.net-core-3.0

Question

I stumbled across this issue today for the first time when trying to return an array of objects from a LINQ query that contains a foreign key field. The move by Microsoft away Newtonsoft JSON Library for .NET Core 3+ has left me not knowing how to perform the equivalent method show below:
Example below used to work in Core 2.2 but now throws an error 'System.Text.Json.JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32.'
public async Task<IActionResult> OnGetSelectAllReportTemplatesAsync()
{
// Get the currently logged in user.
var currentlyLoggedInUser = await _userManager.GetUserAsync(User);
// Note - ApplicationUserId is a foreign key field in the DB Table...
var reportTemplates = _context.ReportTemplate
.Where(s => s.Private == true & s.ApplicationUserId == currentlyLoggedInUser.Id)
.OrderBy(s => s.Name).ToListAsync();
return new JsonResult(reportTemplates);
}
Ajax Call below:
$.ajax({
type: "GET",
url: "/Reports/ListView?handler=SelectAllReportTemplates",
contentType: "json",
dataType: "json",
success: function (data) {
data.forEach(function (element) {
$("#editReportTemplateSelect").append('<option value="' + element.id + '">' + element.name + '</option>');
reportTemplatesArray.push({ id: '' + element.id + '', name: '' + element.name + '', description: '' + element.description + '', timePeriod: '' + element.timePeriod + '', startDate: '' + element.startDate + '', startTimeHours: '' + element.startTimeHours + '', startTimeMinutes: '' + element.startTimeMinutes + '', endDate: '' + element.endDate + '', endTimeHours: '' + element.endTimeHours + '', endTimeMinutes: '' + element.endTimeMinutes + '', logLevel: '' + element.logLevel + '', eventCategory: '' + element.eventCategory + '', eventType: '' + element.eventType + '', eventSource: '' + element.eventSource + '', userAccount: '' + element.userAccount + '', private: '' + element.private + '', });
});
$("#reportTemplateNameInput").val(''); // Clear the department name input field.
$('#reportTemplateDescriptionTextarea').val(''); // Clear the department description textarea.
},
error: function () {
$("#editreportTemplateSelectMessageBar").html("Error while making Ajax call!");
setTimeout(function () { $("#editreportTemplateSelectMessageBar").html(''); }, 5000);
}
});
I tried marking the foreign key field in the model class with attribute '[JsonIgnore]' as i actually don't need to read nested properties from other tables, all i need is the ApplicationUserId string value itself. The only reason I have the tables using a relationship is for cascade delete.
I cant find any code examples which explains how to use the newer system?

Answer 1

OK, so I got my wires crossed a little here, after installing the former JSON functionality (Microsoft.AspNetCore.Mvc.NewtonsoftJson patch) as a NuGet back into the project, i was still getting an object cycle error.
My solution was to set the foreign key field in the model class with the attribute [JsonIgnore], I then updated the OnGet method as below. The method now uses a more simplified LINQ query which passed without errors, I then do the filtering from the selection manually afterwords, creating a list that could then be returned back to the Ajax GET function.
Model Class:
public class ReportTemplate
{
public int Id { get; set; } // Primary Key
other parameter object here...
[Required]
[JsonIgnore]
public string ApplicationUserId { get; set; }
[JsonIgnore]
public ApplicationUser ApplicationUser { get; set; }
}
Razor Page Model:
public async Task<IActionResult> OnGetSelectAllReportTemplates()
{
// Get the currently logged in user.
var currentlyLoggedInUser = await _userManager.GetUserAsync(User);
// Create a List
List<ReportTemplate> reportTemplates = new List<ReportTemplate>();
// Run a simple get all LINQ query
var reports = _context.ReportTemplate.OrderBy(s => s.Name);
// Do the filtering, manually from the query collection
foreach (var report in reports)
{
if (report.Private == false)
{
reportTemplates.Add(report);
}
if (report.Private == true & report.ApplicationUserId == currentlyLoggedInUser.Id)
{
reportTemplates.Add(report);
}
}
return new JsonResult(reportTemplates);
}