Why is there a conflict between my tables in my database?

Question

I get a conflict between my two tables. This is the message.

SqlException: The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Commenents_Tickets_Ticket_Id". The conflict occurred in database "NewTracker", table "dbo.Tickets", column 'Ticket_Id'.

The problem is when I try to submit a message through my view, to store it on my Comment table. I have three tables that are composed, Project has a one to many with Ticket, Then Ticket has a one to many relationship with Comments. From what I can see on my models, does everything seem to match the relationships? So I can not really understand why this error occurs?

Project Model

 public class Project
    {
        [Key]
        public int Project_Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Required]
        public string Description { get; set; }
        public DateTime Created { get; set; }

        List<Ticket> Tickets { get; set; }
    }

Ticket Model

public class Ticket
    {
        [Key]
        public int Ticket_Id { get; set; }
        [Required]
        public string TicketName { get; set; }
        [Required]
        public string TicketDescription { get; set; }

        public DateTime TicketCreated { get; set; }

        public string TicketPriority { get; set; }

        public string TicketType { get; set; }

        public string TicketStatus { get; set; }
       
        List<Comments> Comments { get; set; }


        [ForeignKey("Project")]
        public int Project_Id { get; set; }
        public Project Project { get; set; }


    }

Comments Model

   public class Comments
    {
        [Key]
        public int Comment_Id { get; set; }
        [Required]
        public string Message { get; set; }

        public DateTime Created { get; set; }

        [ForeignKey("Ticket")]
        public int Ticket_Id { get; set; }
        public Ticket Ticket { get; set; }
    }

Here are my TicketController

The ticket controller handle the CRUD operations to Ticket. It also handle Creation for comments as you can see on the bottom of the page. The exception points at the SaveChanges() in Comments at the bottom

{
    [Authorize]
    public class TicketController : Controller
    {
        private readonly ApplicationDbContext _db;

        public TicketController(ApplicationDbContext db)
        {
            _db = db;
        }



        public IActionResult Index()
        {

            IEnumerable<Ticket> objList = _db.Tickets;

            foreach (var obj in objList)
            {
                obj.Project = _db.Projects.FirstOrDefault(u => u.Project_Id == obj.Project_Id);
            }

            return View(objList);

        }

   

        public IActionResult Info(int id)
        {
            CommentVM t = new CommentVM();
            t.Ticket = _db.Tickets.FirstOrDefault(t => t.Ticket_Id == id);
            t.Comments = _db.Commenents.Where(f => f.Ticket_Id == id);
            return View(t);
        }


      



        // Create

        public IActionResult Create(int? id)
        {

            TicketVM obj = new TicketVM();
            obj.ProjectList = _db.Projects.Select(i => new SelectListItem
            {
                Text = i.Name,
                Value = i.Project_Id.ToString()

            });
            if (id == null)
            {
                return View(obj);
            }



            // Status List
            #region
            List<SelectListItem> statusList = new List<SelectListItem>();
            statusList.Add(new SelectListItem()
            {

                Value = "Open",
                Text = "Open"
            });

            statusList.Add(new SelectListItem()
            {

                Value = "Closed",
                Text = "Closed"
            });



            #endregion
            // Status List End

            if (obj == null)
            {
                return NotFound();
            }

            obj.Ticket = _db.Tickets.FirstOrDefault(u => u.Ticket_Id == id);
            obj.StatusList = statusList;


            return View(obj);

        }


        // POST Create/Update
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(TicketVM obj)
        {

           if (obj.Ticket.Ticket_Id == 0)
            {
                _db.Tickets.Add(obj.Ticket);
            }
            else
            {
                _db.Tickets.Update(obj.Ticket);
            }


            
            _db.SaveChanges();
            return RedirectToAction(nameof(Index));

        }



        // Delete

        public IActionResult Delete(int? id)
        {
            var dbObj = _db.Tickets.FirstOrDefault(u => u.Ticket_Id == id);
            _db.Tickets.Remove(dbObj);
            _db.SaveChanges();
            return RedirectToAction("Index");
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Comments(CommentVM obj)
        {
            if (ModelState.IsValid)
            {
                _db.Commenents.Add(obj.Comment);
                _db.SaveChanges();
                return RedirectToAction(nameof(Index));
            }

            return View();
        }


    }
}

Here are my Scripts for the database

CREATE DATABASE [NewTracker]
 CONTAINMENT = NONE
 ON  PRIMARY 
( NAME = N'NewTracker', FILENAME = N'C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\DATA\NewTracker.mdf' , SIZE = 8192KB , MAXSIZE = UNLIMITED, FILEGROWTH = 65536KB )
 LOG ON 
( NAME = N'NewTracker_log', FILENAME = N'C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\DATA\NewTracker_log.ldf' , SIZE = 8192KB , MAXSIZE = 2048GB , FILEGROWTH = 65536KB )
 WITH CATALOG_COLLATION = DATABASE_DEFAULT
GO
ALTER DATABASE [NewTracker] SET COMPATIBILITY_LEVEL = 150
GO
IF (1 = FULLTEXTSERVICEPROPERTY('IsFullTextInstalled'))
begin
EXEC [NewTracker].[dbo].[sp_fulltext_database] @action = 'enable'
end
GO
ALTER DATABASE [NewTracker] SET ANSI_NULL_DEFAULT OFF 
GO
ALTER DATABASE [NewTracker] SET ANSI_NULLS OFF 
GO
ALTER DATABASE [NewTracker] SET ANSI_PADDING OFF 
GO
ALTER DATABASE [NewTracker] SET ANSI_WARNINGS OFF 
GO
ALTER DATABASE [NewTracker] SET ARITHABORT OFF 
GO
ALTER DATABASE [NewTracker] SET AUTO_CLOSE OFF 
GO
ALTER DATABASE [NewTracker] SET AUTO_SHRINK OFF 
GO
ALTER DATABASE [NewTracker] SET AUTO_UPDATE_STATISTICS ON 
GO
ALTER DATABASE [NewTracker] SET CURSOR_CLOSE_ON_COMMIT OFF 
GO
ALTER DATABASE [NewTracker] SET CURSOR_DEFAULT  GLOBAL 
GO
ALTER DATABASE [NewTracker] SET CONCAT_NULL_YIELDS_NULL OFF 
GO
ALTER DATABASE [NewTracker] SET NUMERIC_ROUNDABORT OFF 
GO
ALTER DATABASE [NewTracker] SET QUOTED_IDENTIFIER OFF 
GO
ALTER DATABASE [NewTracker] SET RECURSIVE_TRIGGERS OFF 
GO
ALTER DATABASE [NewTracker] SET  ENABLE_BROKER 
GO
ALTER DATABASE [NewTracker] SET AUTO_UPDATE_STATISTICS_ASYNC OFF 
GO
ALTER DATABASE [NewTracker] SET DATE_CORRELATION_OPTIMIZATION OFF 
GO
ALTER DATABASE [NewTracker] SET TRUSTWORTHY OFF 
GO
ALTER DATABASE [NewTracker] SET ALLOW_SNAPSHOT_ISOLATION OFF 
GO
ALTER DATABASE [NewTracker] SET PARAMETERIZATION SIMPLE 
GO
ALTER DATABASE [NewTracker] SET READ_COMMITTED_SNAPSHOT ON 
GO
ALTER DATABASE [NewTracker] SET HONOR_BROKER_PRIORITY OFF 
GO
ALTER DATABASE [NewTracker] SET RECOVERY FULL 
GO
ALTER DATABASE [NewTracker] SET  MULTI_USER 
GO
ALTER DATABASE [NewTracker] SET PAGE_VERIFY CHECKSUM  
GO
ALTER DATABASE [NewTracker] SET DB_CHAINING OFF 
GO
ALTER DATABASE [NewTracker] SET FILESTREAM( NON_TRANSACTED_ACCESS = OFF ) 
GO
ALTER DATABASE [NewTracker] SET TARGET_RECOVERY_TIME = 60 SECONDS 
GO
ALTER DATABASE [NewTracker] SET DELAYED_DURABILITY = DISABLED 
GO
ALTER DATABASE [NewTracker] SET ACCELERATED_DATABASE_RECOVERY = OFF  
GO
EXEC sys.sp_db_vardecimal_storage_format N'NewTracker', N'ON'
GO
ALTER DATABASE [NewTracker] SET QUERY_STORE = OFF
GO
USE [NewTracker]
GO
/****** Object:  Table [dbo].[__EFMigrationsHistory]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[__EFMigrationsHistory](
    [MigrationId] [nvarchar](150) NOT NULL,
    [ProductVersion] [nvarchar](32) NOT NULL,
 CONSTRAINT [PK___EFMigrationsHistory] PRIMARY KEY CLUSTERED 
(
    [MigrationId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetRoleClaims]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetRoleClaims](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [RoleId] [nvarchar](450) NOT NULL,
    [ClaimType] [nvarchar](max) NULL,
    [ClaimValue] [nvarchar](max) NULL,
 CONSTRAINT [PK_AspNetRoleClaims] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetRoles]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetRoles](
    [Id] [nvarchar](450) NOT NULL,
    [Name] [nvarchar](256) NULL,
    [NormalizedName] [nvarchar](256) NULL,
    [ConcurrencyStamp] [nvarchar](max) NULL,
 CONSTRAINT [PK_AspNetRoles] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetUserClaims]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetUserClaims](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [UserId] [nvarchar](450) NOT NULL,
    [ClaimType] [nvarchar](max) NULL,
    [ClaimValue] [nvarchar](max) NULL,
 CONSTRAINT [PK_AspNetUserClaims] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetUserLogins]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetUserLogins](
    [LoginProvider] [nvarchar](450) NOT NULL,
    [ProviderKey] [nvarchar](450) NOT NULL,
    [ProviderDisplayName] [nvarchar](max) NULL,
    [UserId] [nvarchar](450) NOT NULL,
 CONSTRAINT [PK_AspNetUserLogins] PRIMARY KEY CLUSTERED 
(
    [LoginProvider] ASC,
    [ProviderKey] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetUserRoles]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetUserRoles](
    [UserId] [nvarchar](450) NOT NULL,
    [RoleId] [nvarchar](450) NOT NULL,
 CONSTRAINT [PK_AspNetUserRoles] PRIMARY KEY CLUSTERED 
(
    [UserId] ASC,
    [RoleId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetUsers]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetUsers](
    [Id] [nvarchar](450) NOT NULL,
    [Discriminator] [nvarchar](max) NOT NULL,
    [Name] [nvarchar](max) NULL,
    [UserName] [nvarchar](256) NULL,
    [NormalizedUserName] [nvarchar](256) NULL,
    [Email] [nvarchar](256) NULL,
    [NormalizedEmail] [nvarchar](256) NULL,
    [EmailConfirmed] [bit] NOT NULL,
    [PasswordHash] [nvarchar](max) NULL,
    [SecurityStamp] [nvarchar](max) NULL,
    [ConcurrencyStamp] [nvarchar](max) NULL,
    [PhoneNumber] [nvarchar](max) NULL,
    [PhoneNumberConfirmed] [bit] NOT NULL,
    [TwoFactorEnabled] [bit] NOT NULL,
    [LockoutEnd] [datetimeoffset](7) NULL,
    [LockoutEnabled] [bit] NOT NULL,
    [AccessFailedCount] [int] NOT NULL,
 CONSTRAINT [PK_AspNetUsers] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[AspNetUserTokens]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[AspNetUserTokens](
    [UserId] [nvarchar](450) NOT NULL,
    [LoginProvider] [nvarchar](450) NOT NULL,
    [Name] [nvarchar](450) NOT NULL,
    [Value] [nvarchar](max) NULL,
 CONSTRAINT [PK_AspNetUserTokens] PRIMARY KEY CLUSTERED 
(
    [UserId] ASC,
    [LoginProvider] ASC,
    [Name] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[Commenents]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Commenents](
    [Comment_Id] [int] IDENTITY(1,1) NOT NULL,
    [Message] [nvarchar](max) NOT NULL,
    [Created] [datetime2](7) NOT NULL,
    [Ticket_Id] [int] NOT NULL,
 CONSTRAINT [PK_Commenents] PRIMARY KEY CLUSTERED 
(
    [Comment_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[Projects]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Projects](
    [Project_Id] [int] IDENTITY(1,1) NOT NULL,
    [Name] [nvarchar](max) NOT NULL,
    [Description] [nvarchar](max) NOT NULL,
    [Created] [datetime2](7) NOT NULL,
 CONSTRAINT [PK_Projects] PRIMARY KEY CLUSTERED 
(
    [Project_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
/****** Object:  Table [dbo].[Tickets]    Script Date: 2021-06-08 18:47:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Tickets](
    [Ticket_Id] [int] IDENTITY(1,1) NOT NULL,
    [TicketName] [nvarchar](max) NOT NULL,
    [TicketDescription] [nvarchar](max) NOT NULL,
    [TicketCreated] [datetime2](7) NOT NULL,
    [TicketPriority] [nvarchar](max) NULL,
    [TicketType] [nvarchar](max) NULL,
    [Project_Id] [int] NOT NULL,
    [TicketStatus] [nvarchar](max) NULL,
 CONSTRAINT [PK_Tickets] PRIMARY KEY CLUSTERED 
(
    [Ticket_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [IX_AspNetRoleClaims_RoleId]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_AspNetRoleClaims_RoleId] ON [dbo].[AspNetRoleClaims]
(
    [RoleId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [RoleNameIndex]    Script Date: 2021-06-08 18:47:05 ******/
CREATE UNIQUE NONCLUSTERED INDEX [RoleNameIndex] ON [dbo].[AspNetRoles]
(
    [NormalizedName] ASC
)
WHERE ([NormalizedName] IS NOT NULL)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [IX_AspNetUserClaims_UserId]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_AspNetUserClaims_UserId] ON [dbo].[AspNetUserClaims]
(
    [UserId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [IX_AspNetUserLogins_UserId]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_AspNetUserLogins_UserId] ON [dbo].[AspNetUserLogins]
(
    [UserId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [IX_AspNetUserRoles_RoleId]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_AspNetUserRoles_RoleId] ON [dbo].[AspNetUserRoles]
(
    [RoleId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [EmailIndex]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [EmailIndex] ON [dbo].[AspNetUsers]
(
    [NormalizedEmail] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [UserNameIndex]    Script Date: 2021-06-08 18:47:05 ******/
CREATE UNIQUE NONCLUSTERED INDEX [UserNameIndex] ON [dbo].[AspNetUsers]
(
    [NormalizedUserName] ASC
)
WHERE ([NormalizedUserName] IS NOT NULL)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
/****** Object:  Index [IX_Commenents_Ticket_Id]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_Commenents_Ticket_Id] ON [dbo].[Commenents]
(
    [Ticket_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
/****** Object:  Index [IX_Tickets_Project_Id]    Script Date: 2021-06-08 18:47:05 ******/
CREATE NONCLUSTERED INDEX [IX_Tickets_Project_Id] ON [dbo].[Tickets]
(
    [Project_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
GO
ALTER TABLE [dbo].[Tickets] ADD  DEFAULT ((0)) FOR [Project_Id]
GO
ALTER TABLE [dbo].[AspNetRoleClaims]  WITH CHECK ADD  CONSTRAINT [FK_AspNetRoleClaims_AspNetRoles_RoleId] FOREIGN KEY([RoleId])
REFERENCES [dbo].[AspNetRoles] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetRoleClaims] CHECK CONSTRAINT [FK_AspNetRoleClaims_AspNetRoles_RoleId]
GO
ALTER TABLE [dbo].[AspNetUserClaims]  WITH CHECK ADD  CONSTRAINT [FK_AspNetUserClaims_AspNetUsers_UserId] FOREIGN KEY([UserId])
REFERENCES [dbo].[AspNetUsers] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetUserClaims] CHECK CONSTRAINT [FK_AspNetUserClaims_AspNetUsers_UserId]
GO
ALTER TABLE [dbo].[AspNetUserLogins]  WITH CHECK ADD  CONSTRAINT [FK_AspNetUserLogins_AspNetUsers_UserId] FOREIGN KEY([UserId])
REFERENCES [dbo].[AspNetUsers] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetUserLogins] CHECK CONSTRAINT [FK_AspNetUserLogins_AspNetUsers_UserId]
GO
ALTER TABLE [dbo].[AspNetUserRoles]  WITH CHECK ADD  CONSTRAINT [FK_AspNetUserRoles_AspNetRoles_RoleId] FOREIGN KEY([RoleId])
REFERENCES [dbo].[AspNetRoles] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetUserRoles] CHECK CONSTRAINT [FK_AspNetUserRoles_AspNetRoles_RoleId]
GO
ALTER TABLE [dbo].[AspNetUserRoles]  WITH CHECK ADD  CONSTRAINT [FK_AspNetUserRoles_AspNetUsers_UserId] FOREIGN KEY([UserId])
REFERENCES [dbo].[AspNetUsers] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetUserRoles] CHECK CONSTRAINT [FK_AspNetUserRoles_AspNetUsers_UserId]
GO
ALTER TABLE [dbo].[AspNetUserTokens]  WITH CHECK ADD  CONSTRAINT [FK_AspNetUserTokens_AspNetUsers_UserId] FOREIGN KEY([UserId])
REFERENCES [dbo].[AspNetUsers] ([Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[AspNetUserTokens] CHECK CONSTRAINT [FK_AspNetUserTokens_AspNetUsers_UserId]
GO
ALTER TABLE [dbo].[Commenents]  WITH CHECK ADD  CONSTRAINT [FK_Commenents_Tickets_Ticket_Id] FOREIGN KEY([Ticket_Id])
REFERENCES [dbo].[Tickets] ([Ticket_Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[Commenents] CHECK CONSTRAINT [FK_Commenents_Tickets_Ticket_Id]
GO
ALTER TABLE [dbo].[Tickets]  WITH CHECK ADD  CONSTRAINT [FK_Tickets_Projects_Project_Id] FOREIGN KEY([Project_Id])
REFERENCES [dbo].[Projects] ([Project_Id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[Tickets] CHECK CONSTRAINT [FK_Tickets_Projects_Project_Id]
GO
USE [master]
GO
ALTER DATABASE [NewTracker] SET  READ_WRITE 
GO

Answer 1

This error means the constraint is violated, which means you are making a comment, and either leaving Ticket_Id null, or you're adding ticket id value that doesn't exist in the tickets table

Ticket is the parent table, in order a comment on a ticket, the ticket has to exist first.