Why is ASP.NET Identity 2.0 using a GUID/string as user id?

Question

As the title says, I wonder, why ASP.NET Identity 2.0 uses a string with a GUID as primary clustered key for the user table. Does this have any advantages to an integer id?

Answer 1

A Guid as a UserId (thereby primary key) can be your best friend at times.

Something to consider when folks "rant" against a GUID is they may not be considering "occasionally connected" applications whereby you can't hit the database to get your "int" identity field value until your reconnect but need to create multiple records in various tables linked together offline. Having a Guid allows the application create a "user" and therefore the "userId" as the primary key without collisions when you sync when back online.

To avoid performance hits, don't put the Guid in the cluster index. You can always use a different unique field as the cluster id or maybe even use an integer identity field increased by one as a "clusterId" and use that instead.

Another reason is when you are aggregating data from many different sources, if the UserId (primary key) is a Guid you can avoid collisions.