Implementing Ef Core Skill for Claude

Repository Pattern

EF implementations live in src/Infrastructure/EntityFramework/Repositories/. Each class implements the same interface as its Dapper counterpart. The EF repository uses DbContext and LINQ queries instead of stored procedures, but must produce identical behavior.

Why behavior must match stored procedures exactly

Bitwarden self-hosted runs on the customer's choice of database. If CipherRepository.GetManyByUserId() returns results in a different order on PostgreSQL than the stored procedure returns on MSSQL, or filters differently, or handles nulls differently — that's a bug. Users switching databases or comparing behavior across environments will see inconsistencies.

The [DatabaseData] integration test attribute runs the same test against all configured databases. This is the primary safety net for parity.

Cross-database considerations

EF Core's LINQ-to-SQL translation varies by provider. Patterns that work on one database may fail on another:

• PostgreSQL is stricter about types — operations like Min() on booleans or implicit string/int conversions that MySQL allows will throw
• SQLite has limited ALTER TABLE support — some migrations that work elsewhere fail on SQLite
• Case sensitivity depends on database collation, not on C# code — don't assume case-insensitive string comparison

The pragmatic approach: write clean LINQ, run [DatabaseData] tests, and fix provider-specific failures as they surface rather than trying to predict every edge case.

Migration Generation

Workflow

Run pwsh ef_migrate.ps1 <MigrationName> to generate migrations for all EF targets simultaneously. This creates migration files for each provider (PostgreSQL, MySQL, SQLite).

Why the migration name matters

The EF migration class name must exactly match the MSSQL migration name portion (from the YYYY-MM-DD_##_MigrationName.sql filename). This convention keeps migration history aligned across ORMs and makes it easy to trace which EF migration corresponds to which SQL script.

Always review generated migrations

EF's migration generator makes mechanical decisions that aren't always optimal:

• It may drop and recreate indexes instead of renaming them
• It may generate unnecessary column modifications when model annotations change
• It doesn't know about Bitwarden's large table concerns (never add indexes to Cipher, OrganizationUser etc. without careful review)

Review the generated Up() and Down() methods to ensure they align with the stored procedure migration's intent.

Key Decisions That Trip Up AI Assistants

Don't add navigation properties casually

EF navigation properties (e.g., public virtual Organization Organization { get; set; }) affect query generation and lazy loading behavior. Only add them when the stored procedure equivalent also joins those tables. Unnecessary navigation properties cause N+1 queries that don't match the stored procedure's behavior.

DbContext configuration lives in EntityTypeConfiguration classes

Don't configure entities inline in OnModelCreating. Each entity has a configuration class that defines table mapping, relationships, and constraints. This keeps the DbContext clean and each entity's configuration self-contained.

Respect the same GUID generation strategy

Entity IDs are generated in application code via CoreHelpers.GenerateComb(), not by the database. Don't configure ValueGeneratedOnAdd() or database-generated defaults for ID columns in EF configuration.

Critical Rules

These are the most frequently violated conventions. Claude cannot fetch the linked docs at runtime, so these are inlined here:

• One EntityTypeConfiguration<T> class per entity — never configure inline in OnModelCreating
• Migration name must match MSSQL migration name from YYYY-MM-DD_##_MigrationName.sql
• Run pwsh ef_migrate.ps1 <Name> to generate migrations for all providers simultaneously
• Review Up() and Down() methods in every generated migration before committing
• No ValueGeneratedOnAdd() on ID columns — IDs come from CoreHelpers.GenerateComb() in app code

Examples

GUID configuration

// CORRECT — ID generated in application code
public void Configure(EntityTypeBuilder<Cipher> builder)
{
    builder.HasKey(c => c.Id);
    // No ValueGeneratedOnAdd — CoreHelpers.GenerateComb() handles this
}

// WRONG — lets database generate IDs, breaks MSSQL parity
public void Configure(EntityTypeBuilder<Cipher> builder)
{
    builder.HasKey(c => c.Id);
    builder.Property(c => c.Id).ValueGeneratedOnAdd();
}

Navigation properties

// CORRECT — only add when the SP also joins this table
public class Cipher
{
    public Guid Id { get; set; }
    public Guid OrganizationId { get; set; }
    // No navigation property — the SP doesn't JOIN Organization
}

// WRONG — causes N+1 queries that don't match SP behavior
public class Cipher
{
    public Guid Id { get; set; }
    public Guid OrganizationId { get; set; }
    public virtual Organization Organization { get; set; }
}

Further Reading

• Database migrations (EF)
• SQL code style