Stores.MaxLengthForKeys is not consistent with what is announced

[Ponant]

services.AddDefaultIdentity<IdentityUser>(x=>x.Stores.MaxLengthForKeys=100)
will not generate a Max Length of 100 for UserId; it remains at 450. This is not consitent with the intellisense text
" If set to a positive number, the default OnModelCreating will use this value as the max length for any properties used as keys, i.e. UserId, LoginProvider, ProviderKey."

[blowdart]

Could you tell me which version of identity you're seeing this in?

[Ponant]

On both
2.1.600-preview-009497
2.2.200-preview-009804

the preview is because I am on on the lastest VS 2019 preview

[Ponant]

It is actually worse than that because for the 2.1 version setting 100 as a max will set not only 450 for UserId but will also ignore the 100 for the providers, which remain at 128.
The culprit is most likely here
https://github.com/aspnet/AspNetCore/blob/bfec2c14be1e65f7dd361a43950d4c848ad0cd35/src/Identity/UI/src/IdentityServiceCollectionUIExtensions.cs#L58-L59

[Ponant]

And trying to play with the migrations, e.g. delete the migration folder or simply adding another migration will mix up things you will get 100 for providers but still 450 for USerId. The template I used is the Razor Pages with Auth selected for the sdk's above.

[Ponant]

@blowdart , the inconstency might be due to the following:
services.AddDefaultIdentity<IdentityUser>(x=>x.Stores.MaxLengthForKeys=100)
acts in AddIdentityCore but x.Stores.MaxLengthForKeys=100 is only taken into account in IdentityUserContext https://github.com/aspnet/AspNetCore/blob/bfec2c14be1e65f7dd361a43950d4c848ad0cd35/src/Identity/EntityFrameworkCore/src/IdentityUserContext.cs#L120

This means UserId is not affected by the MaxLengthForKeys in IdentityUserContext (IdentityDbContext inherits from it)
https://github.com/aspnet/AspNetCore/blob/bfec2c14be1e65f7dd361a43950d4c848ad0cd35/src/Identity/EntityFrameworkCore/src/IdentityUserContext.cs#L167 , so this means it is the intellisense info which is wrong.

(Edit: removed a wrong argument)

[blowdart]

We'll consider this next time we break the schema, rather than create a break just for this.

[IndigoHealth]

This SO answer recommends using Stores.MaxLengthForKeys as a workaround for an annoying problem where the migration scaffolder changes the lengths of a bunch of keys (AspNetUserTokens.Name, AspNetUserTokens.LoginProvider, AspNetUserLogins.ProviderKey, AspNetUserLogins.LoginProvider) from 450 to 128 and back again. This github issue documents that problem.