Read-only DbContext

For query code, no-tracking reads and accidental-write guards express intent. Arc offers both a base class and registration helpers, but they are not interchangeable security boundaries.

Define a query context

Model declaration fragment; supply the Customer entity:

using Cratis.Arc.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;

public class StoreDbContext(DbContextOptions<StoreDbContext> options) : ReadOnlyDbContext(options)
{
    public DbSet<Customer> Customers => Set<Customer>();
}

Register it through WithEntityFrameworkCore discovery or this explicit service-registration fragment:

services.AddReadOnlyDbContextWithConnectionString<StoreDbContext>("Data Source=store.db");

Import Microsoft.Extensions.DependencyInjection for service registration.

Inheritance versus registration

Mechanism	Behavior
ReadOnlyDbContext inheritance	Includes BaseDbContext conversions; overrides SaveChanges() and SaveChangesAsync(CancellationToken) to throw; enables eager loading for ordinary navigations
AddReadOnlyDbContext<T>	Registers a pooled factory and scoped context; configures NoTracking and a SaveChanges interceptor; accepts any EF DbContext subclass
AddReadOnlyDbContextWithConnectionString<T>	Adds provider detection to read-only registration; requires a BaseDbContext subclass

Inheritance alone does not override the Boolean acceptAllChangesOnSuccess SaveChanges overloads. Registration’s interceptor protects the SaveChanges path but does not prohibit raw SQL, ExecuteUpdate, ExecuteDelete, or writes through another context. Use database credentials with read-only permissions when preventing writes is a requirement.

Automatic eager loading

ReadOnlyDbContext marks navigations returned by EF’s GetNavigations() as auto-included. Choose purpose-built models and inspect generated queries rather than assuming every relationship is cheap. Skip navigations are not included by that loop.

To disable this behavior globally, add this member to your derived context:

protected override bool IsEagerLoadingEnabled => false;

To skip auto-includes for an individual query:

var customers = await context.Customers.IgnoreAutoIncludes().ToListAsync();

To override a particular navigation, configure it after the base call:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.Entity<Customer>().Navigation(customer => customer.Orders).AutoInclude(false);
}

These are context/query fragments using your application’s entities. EF’s own rules for owned navigations still apply.

Assembly registration

Assembly scanning selects exported, nonabstract ReadOnlyDbContext subclasses and excludes [IgnoreAutoRegistration] types. It does not discover every arbitrary DbContext.

services.AddReadModelDbContextsWithConnectionStringFromAssemblies(
    "Data Source=store.db",
    (serviceProvider, options) => options.EnableDetailedErrors(),
    typeof(StoreDbContext).Assembly);

See automatic database hookup for pooling and tenant limitations, then observation for live query results.