feat: fix EctoAdapter transaction compatibility with Ecto.Adapters.SQL.Sandbox

[Copilot]

Fix EctoAdapter to work with Ecto.Adapters.SQL.Sandbox in nested transactions

Problem Summary

The EctoAdapter fails when used within Repo.transaction blocks in tests using SQL.Sandbox because:

1. The EnforcerServer runs in a separate GenServer process
2. Database connections are locked to the process that starts the transaction
3. Even with Sandbox.allow/3, the EnforcerServer cannot access a connection locked by another process's transaction

Solution Implemented ✅

Code Changes

• Enhanced EctoAdapter with dynamic repo support
• Added get_dynamic_repo field to EctoAdapter struct
• Implemented get_repo/1 helper for runtime repo determination
• Updated all PersistAdapter protocol implementations to use get_repo/1
• Fixed module references to use fully qualified name Acx.Persist.EctoAdapter.get_repo/1
• Maintained full backward compatibility with existing code
• Added comprehensive inline documentation
• Fixed code formatting issues (removed trailing whitespace)

Documentation Created

• guides/sandbox_testing.md - Complete guide covering problem explanation, solution, examples, and best practices
• test/persist/ecto_sandbox_transaction_test.exs - Example test file showing proper setup patterns
• Updated README.md - Added Testing section with link to guide
• Updated EctoAdapter moduledoc - Clear Sandbox compatibility documentation

How Users Should Use This ✅

The recommended solution follows Ecto's official best practices:

setup do
  :ok = Ecto.Adapters.SQL.Sandbox.checkout(MyApp.Repo)
  # Enable shared mode (KEY FIX!)
  Ecto.Adapters.SQL.Sandbox.mode(MyApp.Repo, {:shared, self()})
  
  # Allow EnforcerServer process
  case Registry.lookup(Acx.EnforcerRegistry, "my_enforcer") do
    [{pid, _}] -> Ecto.Adapters.SQL.Sandbox.allow(MyApp.Repo, self(), pid)
    [] -> :ok
  end
  :ok
end

Fixes #43

Original prompt

---

This section details on the original issue you should resolve

<issue_title>EctoAdapter doesn't work with Ecto.Adapters.SQL.Sandbox in nested transactions</issue_title>
<issue_description>## Problem

The EctoAdapter fails when used within a Repo.transaction block in test environments using Ecto.Adapters.SQL.Sandbox. The EnforcerServer runs in a separate process and cannot access the database connection owned by the test process, even when using Sandbox.allow/3.

This is a specific case of the broader issue described in #31, where the problem manifests when Casbin operations are wrapped in application-level transactions.

Error Message

** (DBConnection.ConnectionError) could not checkout the connection owned by #PID<0.462.0>. 
When using the sandbox, connections are shared, so this may imply another process is using a connection. 
Reason: connection not available and request was dropped from queue after 973ms.

Reproduction Steps

1. Setup
# config/test.exs
config :my_app, MyApp.Repo,
  pool: Ecto.Adapters.SQL.Sandbox

# test/support/casbin_case.ex
defmodule MyApp.CasbinCase do
  use ExUnit.CaseTemplate

  setup do
    :ok = Ecto.Adapters.SQL.Sandbox.checkout(MyApp.Repo)
    
    # This doesn't work because EnforcerServer runs in separate process
    case Registry.lookup(Acx.EnforcerRegistry, "my_enforcer") do
      [{enforcer_pid, _}] ->
        Ecto.Adapters.SQL.Sandbox.allow(MyApp.Repo, self(), enforcer_pid)
      [] ->
        :ok
    end
    
    :ok
  end
end


2. Application Code (with transaction)
defmodule MyApp.Authorization.Roles do
  def create_role(role_name, domain, permissions) do
    # Wrapping in transaction for rollback safety
    Repo.transaction(fn ->
      Enum.each(permissions, fn %{resource: resource, action: action} ->
        case Policy.add(role_name, domain, resource, action) do
          :ok -> :ok
          {:error, reason} -> Repo.rollback(reason)
        end
      end)
      
      {:ok, :created}
    end)
  end
end


3. Test (fails)
defmodule MyApp.RolesTest do
  use MyApp.DataCase
  use MyApp.CasbinCase

  test "create role" do
    permissions = [
      %{resource: "orgs", action: "read"},
      %{resource: "users", action: "read"}
    ]

    # This fails with connection error
    assert {:ok, :created} = Roles.create_role("analyst", "*", permissions)
  end
end

When Repo.transaction is called in the test process, it acquires the sandbox connection. When the transaction then calls Policy.add(), which sends a message to the EnforcerServer (a separate process), that server tries to insert into the database using repo.insert(). Even though we've called Sandbox.allow(Repo, test_pid, enforcer_pid), the enforcer cannot access the connection because:

1. The test process owns the connection in a transaction
2. The transaction has locked the connection
3. The EnforcerServer cannot access a connection locked by another process's transaction</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes EctoAdapter doesn't work with Ecto.Adapters.SQL.Sandbox in nested transactions #43

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[hsluoyz]

@copilot Fix failed CI check:

1s
Run mix format --check-formatted
** (Mix) mix format failed due to --check-formatted.
The following files are not formatted:

  * lib/acx/persist/ecto_adapter.ex
  * test/persist/ecto_sandbox_transaction_test.exs

Error: Process completed with exit code 1.

[Copilot]

@copilot Fix failed CI check:

...

Fixed in commit 552788d. Ran mix format on both files to remove trailing whitespace.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)
• repo.hex.pm
  • Triggering command: /usr/lib/erlang/erts-13.2.2.5/bin/inet_gethost 4 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[hsluoyz]

@copilot fix failed compile error:

Run mix compile --warnings-as-errors
Compiling 5 files (.ex)
warning: EctoAdapter.get_repo/1 is undefined (module EctoAdapter is not available or is yet to be defined)
Invalid call found at 6 locations:
  lib/acx/persist/ecto_adapter.ex:196: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.load_policies/1
  lib/acx/persist/ecto_adapter.ex:230: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.load_filtered_policy/2
  lib/acx/persist/ecto_adapter.ex:299: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.add_policy/2
  lib/acx/persist/ecto_adapter.ex:327: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.remove_policy/2
  lib/acx/persist/ecto_adapter.ex:337: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.remove_filtered_policy/4
  lib/acx/persist/ecto_adapter.ex:363: Acx.Persist.PersistAdapter.Acx.Persist.EctoAdapter.save_policies/2

Compilation failed due to warnings while using the --warnings-as-errors option
Error: Process completed with exit code 1.

[Copilot]

@copilot fix failed compile error:

...

Fixed in commit 7809be8. Changed all EctoAdapter.get_repo(adapter) calls within the protocol implementation to use the fully qualified module name Acx.Persist.EctoAdapter.get_repo(adapter) to resolve the compilation error.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)
• repo.hex.pm
  • Triggering command: /usr/lib/erlang/erts-13.2.2.5/bin/inet_gethost 4 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[github-actions]

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