I’m trying to make a project for a holiday application to pass a course in college. Using the latest versions of .net (8) and entity framework, I have already created entities, enums, basic interfaces, etc. In the controller so far there is only the create method for the person class. But I have a problem with data seeding. Below I give code snippets from dbcontext, as well as data seeding classes and a screenshot from the database. I tried doing different variations with seeding, but it always throws an error somewhere. I need urgent help because I can’t see it 🙁

Error message:

Microsoft.EntityFrameworkCore.DbUpdateException: 'An error occurred while saving the entity changes. See the inner exception for details. SqlException: The INSERT statement conflicted with the FOREIGN KEY constraint "FK_People_Teams_Id". The conflict occurred in database "HolidayAppDb", table "dbo.Teams", column 'TeamID'.

Person seeder, the problem occurs when saving first person:

public async Task Seed()
{
    if (await _dbContext.Database.CanConnectAsync())
    {
        if (!_dbContext.HolidayRequests.Any())
        {
            var teamExists = await _dbContext.Teams.AnyAsync();
            if (!teamExists)
            {
                throw new Exception("The team does not exist.");
            }

            var approvedByFirstLeader = _dbContext.People.OrderBy(p => p.Id).First();
            var approvedBySecondLeader = _dbContext.People.OrderByDescending(p => p.Id).First();

            var firstPerson = new Person()
            {
                Id = Guid.NewGuid(),
                FirstName = "Jacek",
                LastName = "Magiera",
                DateOfBirth = new DateTime(1980, 1, 1),
                Position = "Developer",
                StartDate = new DateTime(2020, 1, 1),
                IsFullTime = true,
                ContactDetails = new()
                { City = "Warsaw", Street = "Miodowa", Email = "[email protected]", PhoneNumber = "+48878453875", PostalCode = "42-290" },
                HolidayTimeRemain = 10,
                TeamId = _dbContext.Teams.OrderBy(t => t.TeamID).First().TeamID,
                Team = _dbContext.Teams.OrderBy(t => t.TeamID).First()
            };

            _dbContext.People.Add(firstPerson);
            await _dbContext.SaveChangesAsync();

            firstPerson.HolidayRequests = new List<HolidayRequest>()
                    {
                        new HolidayRequest()
                        {
                            Description = "Winter Vacation",
                            CreatedAt = new DateTime(2022, 1, 1),
                            StartDate = new DateTime(2022, 1, 10),
                            EndDate = new DateTime(2022, 1, 20),
                            Status = HolidayRequestStatusEnum.Completed,
                            Type = HolidayTypeEnum.PaidLeave,
                            IsApproved = true,
                            ApprovedDate = new DateTime(2021, 12, 1),
                            ApprovedBy = approvedByFirstLeader
                        }
                    };

            _dbContext.HolidayRequests.Add(firstPerson.HolidayRequests.First());

            var secondPerson = new Person()
            {
                Id = Guid.NewGuid(),
                FirstName = "Adam",
                LastName = "Nowak",
                DateOfBirth = new DateTime(1985, 1, 1),
                Position = "Developer",
                StartDate = new DateTime(2021, 1, 1),
                IsFullTime = true,
                ContactDetails = new()
                { City = "Krakow", Street = "Zielona", Email = "[email protected]", PhoneNumber = "+48888453875", PostalCode = "30-300" },
                HolidayTimeRemain = 15,
                TeamId = _dbContext.Teams.OrderByDescending(t => t.TeamID).First().TeamID,
                Team = _dbContext.Teams.OrderByDescending(t => t.TeamID).First()
            };

            _dbContext.People.Add(secondPerson);
            await _dbContext.SaveChangesAsync();

            secondPerson.HolidayRequests = new List<HolidayRequest>()
                    {
                        new HolidayRequest()
                        {
                            Description = "Summer Vacation",
                            CreatedAt = new DateTime(2022, 1, 1),
                            StartDate = new DateTime(2022, 7, 10),
                            EndDate = new DateTime(2022, 7, 20),
                            Status = HolidayRequestStatusEnum.Completed,
                            Type = HolidayTypeEnum.PaidLeave,
                            IsApproved = true,
                            ApprovedDate = new DateTime(2021, 12, 1),
                            ApprovedBy = approvedBySecondLeader
                        }
                    };

            _dbContext.HolidayRequests.Add(secondPerson.HolidayRequests.First());
            await _dbContext.SaveChangesAsync();
        }
    }
}

Team seeder:

public async Task Seed()
{
    if (await _dbContext.Database.CanConnectAsync())
    {
        if (!_dbContext.Teams.Any())
        {
            var firstTeam = new Team() { Name = "Team 1", Description = "First team", IsActive = true, Department = "IT" };
            var secondTeam = new Team() { Name = "Team 2", Description = "Second team", IsActive = true, Department = "IT" };

            _dbContext.Teams.Add(firstTeam);
            _dbContext.Teams.Add(secondTeam);
            await _dbContext.SaveChangesAsync();

            firstTeam.TeamLeader = new Person()
            {
                FirstName = "Jan",
                LastName = "Kowalski",
                DateOfBirth = new DateTime(1975, 1, 1),
                Position = "Team Leader",
                StartDate = new DateTime(2019, 1, 1),
                IsFullTime = true,
                ContactDetails = new()
                { City = "Czestochowa", Street = "Miodowa", Email = "[email protected]", PhoneNumber = "+48522456675", PostalCode = "42-200" },
                HolidayTimeRemain = 5,
                TeamId = firstTeam.TeamID
            };

            secondTeam.TeamLeader = new Person()
            {
                FirstName = "Anna",
                LastName = "Kowalska",
                DateOfBirth = new DateTime(1980, 1, 1),
                Position = "Team Leader",
                StartDate = new DateTime(2020, 1, 1),
                IsFullTime = true,
                ContactDetails = new()
                { City = "Warsaw", Street = "Czerwona", Email = "[email protected]", PhoneNumber = "+48555456675", PostalCode = "00-100" },
                HolidayTimeRemain = 14,
                TeamId = secondTeam.TeamID
            };

            _dbContext.Teams.Update(firstTeam);
            _dbContext.Teams.Update(secondTeam);
            await _dbContext.SaveChangesAsync();
        }
    }
}

And the dbcontext class:

public HolidayAppDbContext(DbContextOptions<HolidayAppDbContext> options) : base(options)
{
}

public DbSet<Person> People { get; set; }
public DbSet<HolidayRequest> HolidayRequests { get; set; }
public DbSet<Team> Teams { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    #region Person
    modelBuilder.Entity<Person>(eb =>
    {
        eb.Property(p => p.Id).ValueGeneratedOnAdd();
        eb.Property(p => p.FirstName).IsRequired().HasMaxLength(50);
        eb.Property(p => p.LastName).IsRequired().HasMaxLength(50);
        eb.Property(p => p.HolidayTimeRemain).IsRequired();
        eb.Property(p => p.DateOfBirth).IsRequired();
        eb.Property(p => p.Position).IsRequired().HasMaxLength(50);
        eb.Property(p => p.StartDate).IsRequired();
        eb.Property(p => p.IsFullTime).IsRequired();
        eb.HasOne(p => p.Team).WithMany(t => t.Persons).HasForeignKey(p => p.TeamId).OnDelete(DeleteBehavior.Restrict).IsRequired();
        eb.HasMany(h => h.HolidayRequests).WithOne(p => p.Person).HasForeignKey(p => p.PersonId);
        eb.OwnsOne(c => c.ContactDetails);
    });
    #endregion

    #region HolidayRequest
    modelBuilder.Entity<HolidayRequest>(eb =>
    {
        eb.Property(hr => hr.Description).IsRequired().HasMaxLength(1000);
        eb.Property(hr => hr.StartDate).IsRequired();
        eb.Property(hr => hr.EndDate).IsRequired();
        eb.Property(hr => hr.Status).IsRequired();
        eb.Property(hr => hr.Type).IsRequired();
        eb.Property(hr => hr.IsApproved).IsRequired();
        eb.Property(hr => hr.CreatedAt).IsRequired();
        eb.Property(hr => hr.UpdatedAt).IsRequired();
        eb.HasOne(hr => hr.ApprovedBy).WithMany().HasForeignKey(hr => hr.ApprovedById);
    });
    #endregion

    #region Team
    modelBuilder.Entity<Team>(eb =>
    {
        eb.Property(t => t.Name).IsRequired().HasMaxLength(50);
        eb.Property(t => t.Description).IsRequired().HasMaxLength(1000);
        eb.Property(t => t.IsActive).IsRequired();
        eb.Property(t => t.Department).IsRequired().HasMaxLength(50);
        eb.Property(t => t.CreatedDate).IsRequired();
        eb.Property(t => t.ModifiedDate);
        eb.HasOne(t => t.TeamLeader).WithOne().HasForeignKey<Person>(p => p.Id).IsRequired();
        eb.HasMany(t => t.Persons).WithOne(p => p.Team).HasForeignKey(p => p.TeamId).IsRequired();
    });
    #endregion
}

Person table

Team table

PS: Also why I’m missing the team leader in team table having a reference to this?
Any ideas? Am I missing something?