SqlServer.InMemory

SqlServer.InMemory is not a full SQL Server emulator. It is a testing-oriented EF Core provider/adapter that uses SQLite in-memory as the execution engine and adds SQL Server-inspired compatibility behavior.

The project is a proof of concept for automated tests that want a relational in-memory database with an API close to SQL Server-oriented EF Core setup:

var options = new DbContextOptionsBuilder<AppDbContext>()
    .UseSqlServerInMemory("TestDb")
    .Options;

await using var context = new AppDbContext(options);
await context.Database.EnsureCreatedAsync();

What it is

• A small EF Core adapter for tests.
• A SQLite in-memory backend hidden behind UseSqlServerInMemory.
• A place for SQL Server-inspired compatibility features.
• A foundation for a future partial T-SQL translator.

What it is not

• It is not SQL Server.
• It does not implement TDS, SqlConnection, stored procedures, views, triggers, a query planner, or a full T-SQL parser.
• It does not use Docker, Testcontainers, or a real SQL Server instance.

Projects

src/SqlServer.InMemory          Core options, abstractions, and exceptions.
src/SqlServer.InMemory.Sqlite   SQLite in-memory connection lifecycle and helpers.
src/SqlServer.InMemory.EFCore   EF Core extension, schema normalization, and exception translation.
src/SqlServer.InMemory.TSql     Future T-SQL translator contracts and basic translator POC.
tests/SqlServer.InMemory.Tests  xUnit test coverage for the POC behavior.

Usage

using Microsoft.EntityFrameworkCore;
using SqlServer.InMemory.EFCore;

var options = new DbContextOptionsBuilder<AppDbContext>()
    .UseSqlServerInMemory("TestDb", sqlOptions =>
    {
        sqlOptions.EnforceForeignKeys = true;
        sqlOptions.UseCaseInsensitiveCollation = true;
        sqlOptions.SchemaMode = SqlServerInMemorySchemaMode.PrefixSchemaName;
    })
    .Options;

await using var context = new AppDbContext(options);
await context.Database.EnsureCreatedAsync();

Implemented in this POC

• UseSqlServerInMemory for typed and untyped DbContextOptionsBuilder.
• SQLite in-memory connection opened immediately and kept alive by EF Core options.
• PRAGMA foreign_keys = ON by default.
• SQLSERVER_CI_AS SQLite collation registration.
• Schema normalization:
  • PrefixSchemaName: auth.Users becomes auth_Users.
  • IgnoreSchema: auth.Users becomes Users.
• Basic exception translation for SQLite foreign key and unique constraint errors.
• Automatic raw SQL translation through an EF Core command interceptor.
• Compatibility wrapper that accepts SQL Server DbParameter instances, including Microsoft.Data.SqlClient.SqlParameter, when the SQLite command is created.
• Translation for common test-oriented T-SQL constructs: dbo., N'...', GETDATE(), DATEADD, ISNULL, COUNT_BIG, TOP, OFFSET/FETCH, SET IDENTITY_INSERT, guarded seed inserts, IF OBJECT_ID guards, and OUTPUT INSERTED for simple inserts.
• Core custom exception types.
• Reset helper abstraction and SQLite implementation.
• T-SQL translator abstraction, no-op translator, and basic identifier/TOP translator.

Known limitations

• SQLite type behavior is not SQL Server type behavior.
• Case-insensitive collation is registered, but columns are not automatically rewritten to use it in every model scenario.
• Exception translation is intentionally narrow and based on SQLite error codes.
• Raw SQL translation is automatic, but it uses a regex-based translator intended for tests and known patterns.
• The basic translator is not a full T-SQL parser.
• Complex T-SQL such as MERGE, OUTER APPLY, stored procedures, temporary tables, table variables, dynamic SQL, and arbitrary procedural IF/ELSE blocks are still unsupported unless rewritten into supported patterns.

Roadmap

v0.1 — SQLite backend

• EF Core extension.
• SQLite in-memory.
• FK.
• Unique index.
• Not null.
• Schema normalization.
• Basic exception translation.

v0.2 — SQL Server-like behavior

• Better type mapping.
• Decimal handling.
• Datetime handling.
• Rowversion simulation.
• More SQL Server-like error messages.
• Better collation support.

v0.3 — T-SQL subset translator

• Identifiers.
• Schemas.
• TOP.
• Simple SELECT.
• Simple INSERT.
• Simple UPDATE.
• Simple DELETE.
• Simple CREATE TABLE.
• Simple CREATE INDEX.

v0.4 — Raw SQL integration

• Translator diagnostics.
• Warnings for unsupported T-SQL.
• Configurable translator replacement.
• Optional explicit raw SQL helper APIs if needed.

Running tests

dotnet test SqlServer.InMemory.sln