Tag Archives: OnModelCreating

Short Walks – System.InvalidOperationException: ‘The seed entity for entity type ‘MyEntity’ cannot be added because another seed entity with the same key value for {‘Id’} has already been added. Consider using ‘DbContextOptionsBuilder.EnableSensitiveDataLogging’ to see the conflicting key values.’

I got this error recently while playing with EF Core 2. There’s very little on Google about it; although it’s not a hugely difficult problem to solve, if I ever get it again, I can just Google it !

The error:

System.InvalidOperationException: ‘The seed entity for entity type ‘MyEntity’ cannot be added because another seed entity with the same key value for {‘Id’} has already been added. Consider using ‘DbContextOptionsBuilder.EnableSensitiveDataLogging’ to see the conflicting key values.’

If effectively cause by a conflict in the primary key; and it gives you the first step towards solving it in the error (in OnModelCreating):

var options =
    new DbContextOptionsBuilder<ApplicationDbContext>()
         .UseSqlServer(configuration.GetConnectionString("DefaultConnection"))
         .EnableSensitiveDataLogging()
         .Options;

Now it says:

System.InvalidOperationException: ‘The seed entity for entity type ‘MyEntity’ cannot be added because another seed entity with the key value ‘Id:1′ has already been added.’

In my particular case, I’d been playing around with adding some seed data, and had left this in (OnModelCreating):

modelBuilder.Entity<MyEntity>().HasData(new Data.MyEntity()
{
    Id = 1,
    Name = "Test",
    CreatedDate = new DateTime(2018, 07, 03),
    UpdatedDate = new DateTime(2018, 07, 03)
});

Short Walks – Data Seeding in Entity Framework Core 2

Entity Framework Core 2.1 has a nice little feature for seed data. Previously, seeding data quite often involved a series of checks and potential for a script to exist that, if run on the wrong data, would repeatedly re-generate the same seed data.

In 2.1, you can simply override the OnModelCreating function of the data context, like so:

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }
 
    public DbSet<ResourceType> ResourceType { get; set; }
 
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
 
        modelBuilder.Entity<ResourceType>().HasData(new Data.ResourceType()
        {
            Id = 1,
            Name = "Web Site"                
        });
    }

And the framework will calculate whether or not this needs to run to put the data into the state that you’ve requested.

References

https://docs.microsoft.com/en-us/ef/core/modeling/data-seeding