[*.cs]
dotnet_diagnostic.LC052.severity = error

LC052: Model data uses a value that changes on every run

In Plain Terms

You write “today’s date” on a form that is supposed to be a master copy. Every time someone checks the copy against the original, they differ, so everyone thinks the form was changed.

Goal

Detect DateTime.Now, DateTime.UtcNow, DateTime.Today, DateTimeOffset.Now, DateTimeOffset.UtcNow, Guid.NewGuid(), and Guid.CreateVersion7() inside HasData(...) seed data and HasDefaultValue(...).

The Problem

Seed data and column defaults are part of the EF Core model. The migration snapshot stores their values. When a value comes from the clock or a new GUID, every run builds a different model than the last migration recorded:

// Violation: a new timestamp and key on every run.
modelBuilder.Entity<Blog>().HasData(new Blog { Id = 1, Key = Guid.NewGuid(), CreatedAt = DateTime.UtcNow });

// Violation: the column default is frozen at whenever the model was built.
modelBuilder.Entity<Blog>().Property(b => b.CreatedAt).HasDefaultValue(DateTime.UtcNow);

• dotnet ef migrations add produces a new migration that updates the seed rows each time, even with no real change.
• Since EF Core 9, Migrate() and dotnet ef database update throw PendingModelChangesWarning because the model never matches the snapshot. The EF Core 9 breaking changes name these calls as the usual cause.
• A HasDefaultValue(DateTime.UtcNow) default is not “now” at insert time. It is the time the migration was generated.

The Fix

Seed fixed literals, and let the database supply “now” for column defaults:

modelBuilder.Entity<Blog>().HasData(new Blog
{
    Id = 1,
    Key = new Guid("8c1d2f6e-7a55-4c43-9a2a-1f8b3e6d9c01"),
    CreatedAt = new DateTime(2024, 1, 1, 0, 0, 0, DateTimeKind.Utc)
});

modelBuilder.Entity<Blog>().Property(b => b.CreatedAt).HasDefaultValueSql("GETUTCDATE()"); // SQL Server

For data that really must be generated at runtime, use UseSeeding / UseAsyncSeeding (EF Core 9+) instead of HasData.

Analyzer Logic

ID: LC052

Category: Reliability

Severity: Warning

1. Find calls to EF Core’s HasData (entity and owned-type builders) and HasDefaultValue.
2. Look through every argument, including object initializers, anonymous objects, and arrays.
3. Report each clock or new-GUID value found, directly or through up to three locals or static readonly fields whose only value contains one.

When it stays quiet (non-goals)

• Fixed values: new DateTime(...), new Guid("..."), literals, and constants.
• HasDefaultValueSql(...) and HasComputedColumnSql(...), which run in the database.
• Locals that are written again after their declaration, instance fields, and mutable static fields. The rule cannot prove what they hold when the model is built.
• Values returned from helper methods.
• HasData methods that are not EF Core’s.

Why There Is No Code Fix

No automatic fix. A seed value needs a fixed literal that only the author can choose, and a database default needs provider-specific SQL (GETUTCDATE() on SQL Server, now() on PostgreSQL, CURRENT_TIMESTAMP on SQLite).

Test Cases

Violations

modelBuilder.Entity<Blog>().HasData(new Blog { Id = 1, CreatedAt = DateTime.Now });
modelBuilder.Entity<Blog>().HasData(new { Id = 1, Key = Guid.NewGuid() });
modelBuilder.Entity<Blog>().Property(b => b.CreatedAt).HasDefaultValue(DateTime.UtcNow);

Valid

modelBuilder.Entity<Blog>().HasData(new Blog { Id = 1, CreatedAt = new DateTime(2024, 1, 1) });
modelBuilder.Entity<Blog>().Property(b => b.CreatedAt).HasDefaultValueSql("CURRENT_TIMESTAMP");