Clarification for GUID generation behavior in EF Core 5.0 for SQL Server

[felinepc]

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If a developer's goal is to have “sequential” GUID primary keys generated for faster performance, either by EF Core or the SQL Server’s NEWSEQUENTIALID, what is the expected behavior in EF Core 5.0 and what is the best practice?

This documentation says:

(SequentialGuidValueGenerator Class) Generates sequential Guid values optimized for use in Microsoft SQL server clustered keys or indexes, yielding better performance than random values. This is the default generator for SQL Server Guid columns which are set to be generated on add."

Does this mean if we don’t configure anything on a GUID property at all, EF Core 5 will automatically use its optimized sequential GUID generator to generate a non-temporary sequential GUID that will be saved to the DB? Or do we have to specify ValueGeneratedOnAdd?

But then there is this other documentation which says something different:

How the value is generated for added entities will depend on the database provider being used. Database providers may automatically set up value generation for some property types, but others may require you to manually set up how the value is generated.

For example, when using SQL Server, values will be automatically generated for GUID properties (using the SQL Server sequential GUID algorithm)…

This seems to contradict the first link, which said the GUIDs would be generated on client side.

Some clarifications on this behavior and best practice would be appreciated, since we’d often opt to use GUID instead of int for primary keys to avoid giving away business information to end users.

It would also be nice to know the best approach to take when we do want non-sequential, random GUIDs for properties that are security-sensitive.

Thank you!

Include provider and version information

EF Core version: 5.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 5.0
Operating system: Windows 10 Pro
IDE: Visual Studio 2019 16.8.3

[ajcvickers]

@felinepc This statement:

For example, when using SQL Server, values will be automatically generated for GUID properties (using the SQL Server sequential GUID algorithm)

is intended to indicate that SequentialGuidValueGenerator is used. However, I can see that this could be interpreted as you did, so we could make this clearer.

[felinepc]

SequentialGuidValueGenerator

Thanks. Just to clarify, is SequentialGuidValueGenerator now the default GUID generator for EF Core 5.0 entity class GUID key properties by convention? Asking this because EF Core Github seems to contain both GuidValueGenerator and SequentialGuidValueGenerator, but it's unclear which one is used.

[ajcvickers]

SequentialGuidValueGenerator is the default when using the SQL Server provider. This hasn't changed--it's been this way since 1.0.

[roji]

Yeah, the original intention was to say that the SQL Server algorithm would be used (but on the client-side).

Since then, investigation in dotnet/efcore#19124 (which contains lots of other relevant info) has shown that EF Core isn't actually implementing the SQL Server algorithm, though it's still generating optimal sequential GUIDs. We should indeed update.