ExcelController.cs

using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using StamAcasa.Api.Services.Excel;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace StamAcasa.Api.Controllers {
    [Route("api/[controller]")]
    [ApiController]
    public class ExcelController : ControllerBase {

        IAnswersExcelExporter AnswersExcelExporter { get; }

        class Form {

            public int? formId { get; set; }
            public long? timestamp { get; set; }
            public int? age { get; set; }
            public bool? isSomeTestBoolean { get; set; }
            public DateTime? someDate { get; set; }
            public string name { get; set; }

            public List<Answer> answers { get; set; } = new List<Answer>();

        }

        class Answer {

            public string id { get; set; }
            public string questionText { get; set; }
            public string answer { get; set; }

        }

        public ExcelController(
            IAnswersExcelExporter answersExcelExporter
        ) {
            AnswersExcelExporter = answersExcelExporter;
        }

        [HttpGet]
        public IActionResult Get() {

            var forms = new List<Form>() {
                new Form() {
                    formId = 1,
                    timestamp = 20200327193822,
                    age = 37,
                    isSomeTestBoolean = true,
                    someDate = DateTime.Now,
                    name = "Ted",
                    answers = {
                        new Answer() {
                            id = "101",
                            questionText = "Când ați intrat in contact cu alte persoane ultima data?",
                            answer = "Ieri"
                        },
                        new Answer() {
                            id = "102",
                            questionText = "Ce simptome aveți?",
                            answer = "Tuse seacă, febră"
                        },
                        new Answer() {
                            id = "103",
                            questionText = "Intrebarea numarul 3?",
                            answer = "Da"
                        }
                    }
                },
                new Form() {
                    formId = 2,
                    timestamp = 20200328243524,
                    age = 22,
                    answers = {
                        new Answer() {
                            id = "104",
                            questionText = "Când ați intrat in contact cu alte persoane ultima data?",
                            answer = "Astăzi"
                        }
                    }
                }
            };

            var jObjectsSerialized = JsonConvert.SerializeObject(forms);
            var jArray = JArray.Parse(jObjectsSerialized);

            var fileBinary = AnswersExcelExporter.AnswersToExcel(jArray, AnswersExcelTemplateTypes.MultipleRowsPerForm);

            return File(fileBinary, "application/vnd.ms-excel", "Answers.xlsx");
        }

    }
}