S8718 — Client-evaluated default values should use database functions

Using runtime-evaluated expressions (e.g., DateTime.UtcNow, Guid.NewGuid()) as default values for a property causes the value to be hardcoded as a static value in the database schema, rather than computed per row. This affects HasDefaultValue() in Fluent API configurations and defaultValue in migration files.

Why is this an issue?

• The Cause: These C# expressions evaluate once when the model builds or the migration runs, rather than dynamically by the database.
• The Result: Every new record receives that exact same static value — the same timestamp, or the same GUID — instead of a value computed at insertion time.

Starting with EF Core 9, this also throws an InvalidOperationException for the PendingModelChangesWarning warning when applying migrations, because the default value expression evaluates to a new value on each model build, making migrations non-deterministic.

How to fix it

Replace HasDefaultValue() with HasDefaultValueSql() in Fluent API configurations, and replace defaultValue with defaultValueSql in migration files. This instructs EF Core to let the database engine generate the value at insertion time, using the equivalent function for your database provider:

Some provider-specific quirks to be aware of when picking a replacement:

• MySQL’s UUID() returns a version 1 UUID, not version 4; MariaDB additionally provides a dedicated UUID_v4().
• Oracle’s SYS_GUID() returns a raw 16-byte value, not formatted as a standard hyphenated UUID string.
• SQLite has no native UUID generation function of any version; generate the value in application code instead.
• SQLite and Oracle have no time-zone-aware temporal type, so DateTimeOffset values don’t map cleanly to a single database type.

Code examples

Noncompliant code example

public void Configure(EntityTypeBuilder<Student> builder)
{
    builder.HasKey(x => x.StudentId);
    builder.Property(x => x.EnrollmentDate)
        .IsRequired(true)
        .HasDefaultValue(DateTime.Now); // Noncompliant
}

Compliant solution

public void Configure(EntityTypeBuilder<Student> builder)
{
    builder.HasKey(x => x.StudentId);
    builder.Property(x => x.EnrollmentDate)
        .IsRequired(true)
        .HasDefaultValueSql("GETDATE()"); // SQL Server example — see the table above for other providers
}

Noncompliant code example

migrationBuilder.AddColumn<DateTime>(
    name: "EnrollmentDate",
    table: "Students",
    nullable: false,
    defaultValue: DateTime.UtcNow); // Noncompliant

Compliant solution

migrationBuilder.AddColumn<DateTime>(
    name: "EnrollmentDate",
    table: "Students",
    nullable: false,
    defaultValueSql: "GETUTCDATE()"); // SQL Server example — see the table above for other providers

Noncompliant code example

public void Configure(EntityTypeBuilder<Student> builder)
{
    builder.HasKey(x => x.StudentId);
    builder.Property(x => x.TranscriptId)
        .HasDefaultValue(Guid.NewGuid()); // Noncompliant
}

Compliant solution

public void Configure(EntityTypeBuilder<Student> builder)
{
    builder.HasKey(x => x.StudentId);
    builder.Property(x => x.TranscriptId)
        .HasDefaultValueSql("NEWID()"); // SQL Server example — see the table above for other providers
}

Resources

Documentation

• Microsoft Learn - Entity Framework Core - Default Values
• Microsoft Learn - Date/time value generation
• Microsoft Learn - SQL Server GETDATE() Function
• Microsoft Learn - EF Core 9 - Pending model changes