HasData seeding causes Add to fail with PostgresException: 23505 on calling SaveChanges

Npgsql.EntityFrameworkCore.PostgreSQL version: 2.2.0-preview1

HasData seeding causes Add to fail when calling SaveChangesAsync.

Example:

public class Item 
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class ItemConfiguration : IEntityTypeConfiguration<Item>
{
    public void Configure(EntityTypeBuilder<ProductGroup> builder)
    {
        builder.HasData(new Item { Id = 1, Name = "Test" });
    }
}

Now when you want to add new Item, this code won’t work and will cause PostgresException: 23505:

var item = new Item { Name = "Cool item" };
db.Add(item);
await db.SaveChangesAsync(); // PostgresException: 23505

Note that this code will work fine if we won’t use HasData.

What you have to do instead, you have to set Id explicitly to 0:

var item = new Item { Id = 0, Name = "Cool item" }; // default or default(int) doesn't work, it must be 0...

Or it starts to work too after inserting the item manually using some DB manager.

I think https://github.com/npgsql/Npgsql.EntityFrameworkCore.PostgreSQL/issues/367 and https://github.com/npgsql/Npgsql.EntityFrameworkCore.PostgreSQL/issues/573 is related?

[BojidarStanchev]

-1 is more negative, we need more positivity in the world. Now seriously, -1 is not worse technically. But me having to manually write this in the migrations sucks, Especially during development because migrations will get deleted multiple times, then you forget to add 1 line there (or maybe someone else in the team doesn’t yet know about this problem). This will result in a lot of time wasted on debugging.

If you consider how many people wasted a few hours researching why this happens there are probably thousands of work hours lost because of this not working as intended.

[bugproof]

Don’t use HasData: https://github.com/aspnet/EntityFramework.Docs/issues/1055