How to insert data into sitecore forms programmatically through c# code with custom MVC form ?

To insert the form’s data into sitecore forms you need to perform following steps
-First we need to create a form in sitecore experience forms editor , lets call it "NewForm" where I have created two fields just to keep it simple.
-Then you can create following methods in the controller to post the form

 public ActionResult NewForm()
        {
            return View();
        }
        [HttpPost]
        public ActionResult NewForm(PersonModel pm)
        {
            bool status = false;
            string message = String.Empty;
            try
            {
                //sitecore fields ids
                string NameFieldId = "{B8369FDC-6E08-4054-A89A-FF00D77B1E98}";
                string EmailFieldId = "{B7C86CE0-4FC5-47FE-9C9E-9B3D064C6204}";
                //sitecore form's id
                Guid formId = new Guid("{80E70780-95F7-46A5-8C69-09E89AB5FEF2}");
                //List of field ID, Value pair that needs to be passed onto Experience Forms database. 
                var formFieldList = new List<FormFieldDataModel>();
                //Get the submitted form field data in the format that is needed by Experience Forms model 
                var formNameData = GetNewFormFieldData(NameFieldId, pm.Name);
                formFieldList.Add(formNameData);
                var formEmailData = GetNewFormFieldData(EmailFieldId, pm.Email);
                formFieldList.Add(formEmailData);
                _FormsRepository.SaveNewFormData(formId, formFieldList);

                status = true;
                message = "success";
            }
            catch (Exception ex)
            {
                status = false;
                message = ex.Message;
            }
            ViewBag.status = status;
            ViewBag.message = message;
            
            return Redirect(Request.UrlReferrer.ToString()+"?status=success");
        } 
private FormFieldDataModel GetNewFormFieldData(string fieldId, string fieldValue)
        {
            if (fieldId == null)
                return new FormFieldDataModel();
            var fieldItem = ItemHelper.GetItem(new Sitecore.Data.ID(fieldId));
            if (fieldItem == null) return new FormFieldDataModel();
            var formData = new FormFieldDataModel
            {
                FormFieldName = fieldItem.Name,
                FormFieldGuid = fieldItem.ID.ToGuid(),
                FormFieldValue = fieldValue,
            };
            return formData;
        }

-ItemHelper Class that is being used in above code

using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.Links;
using Sitecore.Web;
using System;
using System.Collections.Generic;
using System.Linq;
public static class ItemHelper
{
    public static Database GetCurrentDatabase()
    {
        if (Sitecore.Context.Database != null)
        {
            return Sitecore.Context.Database;
        }
        return Sitecore.Configuration.Factory.GetDatabase("master");
    }   
    public static Item GetItem(Sitecore.Data.ID id)
    {
        return GetCurrentDatabase().GetItem(id);
    }
}

-Then we can create following two Models

public class FormFieldDataModel
        {
            public string FormFieldValue { get; set; }
            public Guid FormFieldGuid { get; set; }
            public string FormFieldName { get; set; }
        }
        public class PersonModel
        {
            public string Name { get; set; }
            
            public string Email { get; set; }
        }

-Now we can create following repository method to save the form to the database

 [Service(typeof(INewFormRepo))]
        public class NewFormRepo : INewFormRepo
        {
            private IFormDataProvider _dataProvider;
            public NewFormRepo(IFormDataProvider dataProvider)
            {
                _dataProvider = dataProvider;
            }
            public void SaveNewFormData(Guid formId, List<FormFieldDataModel> formFieldDataList)
            {
                Guid sessionId = Guid.NewGuid();
                FormEntry formEntry = new FormEntry()
                {
                    Created = DateTime.Now,
                    FormItemId = formId,
                    FormEntryId = sessionId,
                    Fields = new List<FieldData>()
                };
                foreach (var item in formFieldDataList)
                {
                    AddNewFormFieldData(item, formEntry);
                }
                _dataProvider.CreateEntry(formEntry);
            }

            protected void AddNewFormFieldData(FormFieldDataModel postedField, FormEntry formEntry)
            {
                string str = "System.String";
                string fieldValue = postedField.FormFieldValue;
                FieldData fieldData = new FieldData()
                {
                    FieldDataId = Guid.NewGuid(),
                    FieldItemId = postedField.FormFieldGuid,
                    FormEntryId = formEntry.FormEntryId,
                    FieldName = postedField.FormFieldName,
                    Value = fieldValue,
                    ValueType = str
                };
                formEntry.Fields.Add(fieldData);
            }
        }
        public interface INewFormRepo
        {
            void SaveNewFormData(Guid formId, List<FormFieldDataModel> formFieldDataList);
        }

-Now we can simply call the controller method from our mvc view as shown.

@using (Html.BeginForm("NewForm", "Forms", FormMethod.Post))
                    {
                        <table cellpadding="0" cellspacing="0">
                            <tr>
                                <th colspan="2" align="center">Person Details</th>
                            </tr>
                            <tr>
                                <td>Name: </td>
                                <td>
                                    @Html.TextBoxFor(m => m.Name)
                                </td>
                            </tr>
                            <tr>
                                <td>Email: </td>
                                <td>
                                    @Html.TextBoxFor(m => m.Email)
                                </td>
                            </tr>
                            <tr>
                                <td></td>
                                <td><input type="submit" value="Submit" /></td>
                            </tr>

                        </table>
                    }
                    <p>@ViewBag.status @ViewBag.message</p>