WFFM - Sequential Number Custom Field

SequentialNumber.cs

using System.ComponentModel;
using System.ComponentModel.Design;
using Sitecore.Configuration;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.Form.Core.Attributes;
using Sitecore.Form.Web.UI.Controls;
using Sitecore.SecurityModel;

namespace WesleyLomax.WFFM
{
    [Designer("System.Windows.Forms.Design.ParentControlDesigner, System.Design", typeof(IDesigner))]
    public class SequentialNumber : SingleLineText
    {
        private bool _isHidden = true;
        private string _sequentialNumberId;
        private int _numberPadding;

        [VisualCategory("Sequence")]
        [VisualFieldType(typeof(Fields.SequentialNumberField))]
        [VisualProperty("Sequence:", 100)]
        public string SequentialNumberId
        {
            get { return _sequentialNumberId; }
            set { _sequentialNumberId = value; }
        }

        [VisualCategory("Sequence")]
        [VisualProperty("Length:", 200), DefaultValue("6")]
        public int NumberPadding
        {
            get { return _numberPadding; }
            set { _numberPadding = value; }
        }

        [VisualCategory("Sequence")]
        [VisualFieldType(typeof(Sitecore.Form.Core.Visual.BooleanField))]
        [VisualProperty("Hidden:", 300), DefaultValue("Yes")]
        public string IsHidden
        {
            get { return _isHidden ? "Yes" : "No"; }
            set { _isHidden = value == "Yes"; }
        }
    }
}

SequentialNumberField.cs

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.Form.Core.Configuration;
using Sitecore.Form.Core.Visual;

namespace WesleyLomax.WFFM.Fields
{
    public class SequentialNumberField : ValidationField
    {
        private static readonly ID SequentialFormNumbers = new ID("{C7FB3754-A0B1-469C-9591-7CE3DC075272}");

        public SequentialNumberField() : base(HtmlTextWriterTag.Select.ToString())
        {
        }

        public override bool IsCacheable => false;

        private static Item SequentialFormNumbersRoot => StaticSettings.ContextDatabase.GetItem(SequentialFormNumbers);

        protected override void OnPreRender(object sender, EventArgs ev)
        {
            Controls.Clear();
            base.OnPreRender(sender, ev);
            Controls.Add(new Literal
            {
                Text = string.Format("<option {0} value='{1}'>{1}</option>", DefaultValue == EmptyValue ? "selected='selected'" : string.Empty, EmptyValue)
            });
            foreach (Item child in SequentialFormNumbersRoot.Children)
                Controls.Add(new Literal
                {
                    Text =
                        string.Format("<option {0} value='{1}'>{2}</option>",
                            DefaultValue == child.Fields[FieldIDs.MetaDataListItemValue].Value ? "selected='selected'" : string.Empty,
                            child.ID.ToShortID(),
                            child.DisplayName)
                });
        }
    }
}

SequentialNumberFieldModel.cs

using System;
using Sitecore.Configuration;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.Forms.Mvc.Models.Fields;
using Sitecore.SecurityModel;

namespace WesleyLomax.WFFM.MVCModels
{
    public class SequentialNumberField : SingleLineTextField
    {
        public SequentialNumberField(Item item) : base(item)
        {
            Initialize();
        }
        public override object Value { get; set; }

        private void Initialize()
        {
            string isHidden = Sitecore.Forms.Mvc.Extensions.DictionaryExtensions.GetValue(ParametersDictionary, "isHidden");

            if (!string.IsNullOrWhiteSpace(isHidden) && isHidden.ToUpper() == "YES")
            {
                if (!string.IsNullOrWhiteSpace(CssClass))
                {
                    CssClass += " hidden";
                }
                else
                {
                    CssClass = "hidden";
                }
            }
            else
            {
                if (!string.IsNullOrWhiteSpace(CssClass))
                {
                    CssClass += " disabled";
                }
                else
                {
                    CssClass = "disabled";
                }
            }

            string sequentialNumberId = Sitecore.Forms.Mvc.Extensions.DictionaryExtensions.GetValue(ParametersDictionary, "sequentialNumberId");

            if (!string.IsNullOrWhiteSpace(sequentialNumberId) && ShortID.IsShortID(sequentialNumberId))
            {
                ID id = ShortID.DecodeID(sequentialNumberId);

                if (!id.IsNull)
                {
                    Database master = Factory.GetDatabase("master");

                    if (master != null)
                    {
                        Item sequenceItem = master.GetItem(id);

                        string number = sequenceItem.Fields[Sitecore.Form.Core.Configuration.FieldIDs.MetaDataListItemValue].Value;
                        int padding = Convert.ToInt32(Sitecore.Forms.Mvc.Extensions.DictionaryExtensions.GetValue(ParametersDictionary, "numberPadding"));

                        int currentNumber;

                        if (int.TryParse(number, out currentNumber))
                        {
                            currentNumber++;

                            string sequence = currentNumber.ToString().PadLeft(padding, '0');

                            Value = sequence;
                            

                            using (new SecurityDisabler())
                            {
                                sequenceItem.Editing.BeginEdit();
                                sequenceItem.Fields[Sitecore.Form.Core.Configuration.FieldIDs.MetaDataListItemValue].Value = sequence;
                                sequenceItem.Editing.EndEdit();
                            }
                        }
                    }
                }
            }
        }
    }
}