Add LoadPolicy API for database adapters

[Copilot]

EctoAdapter auto-saves policies to the database but provided no built-in way to load them back on startup, forcing manual database queries and policy reconstruction.

Changes

Added overloaded functions to load from configured adapter:

• EnforcerServer.load_policies/1 - loads policies without requiring file path
• EnforcerServer.load_mapping_policies/1 - loads role mappings without requiring file path

These leverage existing Enforcer.load_policies!/1 and Enforcer.load_mapping_policies!/1, exposing adapter-based loading at the server level.

Backward compatible:

• File-based variants (load_policies/2, load_mapping_policies/2) unchanged
• Existing code unaffected

Usage

Before:

# Manual workaround required
rules = Repo.all(Acx.Persist.EctoAdapter.CasbinRule)
Enum.each(rules, fn rule ->
  case rule.ptype do
    "p" -> EnforcerServer.add_policy(name, {:p, build_attrs([...])})
    "g" -> EnforcerServer.add_mapping_policy(name, {:g, ...})
  end
end)

After:

adapter = EctoAdapter.new(Repo)
EnforcerServer.set_persist_adapter("my_enforcer", adapter)
EnforcerServer.load_policies("my_enforcer")
EnforcerServer.load_mapping_policies("my_enforcer")

Implements LoadPolicy API pattern per maintainer feedback.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>EctoAdapter: No Built-in Way to Load Policies from Database on Startup</issue_title>
<issue_description>## Summary
The EctoAdapter automatically saves policies to the database but provides no clean way to load them back into the enforcer's memory on application startup. This creates an asymmetric API and forces developers to implement manual workarounds.

Current Behavior

What Works (Auto-Save)

# Configure adapter
adapter = EctoAdapter.new(Repo)
EnforcerServer.set_persist_adapter("my_enforcer", adapter)

# Add policy - automatically saved to DB
EnforcerServer.add_policy("my_enforcer", {:p, ["admin", "data", "write", "org:abc"]})
# ✅ Policy is now in both memory AND database

What Doesn't Work (No Auto-Load)

# Application restart...

# Re-configure adapter
adapter = EctoAdapter.new(Repo)
EnforcerServer.set_persist_adapter("my_enforcer", adapter)

# ❌ Policies from database are NOT loaded into memory
EnforcerServer.allow?("my_enforcer", ["admin", "data", "write", "org:abc"])
# => false (policies exist in DB but not in memory)

Expected API

There should be a clean, built-in way to load policies from the database:
# Option 1: Automatic on adapter setup
adapter = EctoAdapter.new(Repo)
EnforcerServer.set_persist_adapter("my_enforcer", adapter, load: true)

# Option 2: Explicit load function
EnforcerServer.load_policies_from_adapter("my_enforcer")

# Option 3: Enhanced load_policies that works with adapters
EnforcerServer.load_policies("my_enforcer", :from_adapter)

Current Workaround (Manual Implementation)

Developers must implement their own loading logic by querying the database directly and manually adding each policy:

defp load_policies_from_db do
  # Manually query the database
  rules = Repo.all(Acx.Persist.EctoAdapter.CasbinRule)

  # Manually add each rule to the enforcer's memory
  Enum.each(rules, fn rule ->
    case rule.ptype do
      "p" ->
        attrs = build_attrs([rule.v0, rule.v1, rule.v2, rule.v3, rule.v4, rule.v5, rule.v6])
        EnforcerServer.add_policy(@enforcer_name, {:p, attrs})


      "g" ->
        attrs = build_attrs([rule.v0, rule.v1, rule.v2])
        case length(attrs) do
          3 ->
            [child, parent, domain] = attrs
            EnforcerServer.add_mapping_policy(@enforcer_name, {:g, child, parent, domain})
          2 ->
            [child, parent] = attrs
            EnforcerServer.add_mapping_policy(@enforcer_name, {:g, child, parent})
        end
    end
  end)
end

defp build_attrs(values) do
  Enum.reject(values, &is_nil/1)
end

Why This is Problematic

1. The set_persist_adapter/2 function suggests persistence is fully configured, but it only handles saves, not loads.
2. New users expect load_policies/2 to work with adapters, but it only accepts file paths:

# This signature is misleading:
EnforcerServer.load_policies(name, file)
# "file" parameter suggests it ONLY loads from files

3. Comparison with PersistAdapter.load_policies/1

The library DOES have a function that retrieves policies from the adapter:
{:ok, {policies, grouping_policies}} = Acx.Persist.PersistAdapter.load_policies(adapter)

But: There's no function to feed these policies back into the enforcer's memory. Developers must manually loop through and add each one.

Proposed Solutions

Option 1: Add load_policies_from_adapter/1
EnforcerServer.load_policies_from_adapter("my_enforcer")

Option 2: Enhance set_persist_adapter/3 with options
EnforcerServer.set_persist_adapter("my_enforcer", adapter, auto_load: true)

Option 3: Make load_policies/2 adapter-aware
Accept atom :adapter as second parameter
EnforcerServer.load_policies("my_enforcer", :adapter)

Option 4: Add Enforcer.load_policies_from_adapter/2
enforcer = Enforcer.init(model_path)
enforcer = Enforcer.load_policies_from_adapter(enforcer, adapter)</issue_description>

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

@hsluoyz Casbin adapters use LoadPolicy API to load policy from DB

Why not use LoadPolicy? If LoadPolicy is not supported, need to support it

Refer to Golang's adapters:

• https://github.com/casbin/gorm-adapter
• https://github.com/casbin/ent-adapter
• https://github.com/casbin/xorm-adapter
• https://github.com/casbin/redis-adapter</comment_new>

• Fixes EctoAdapter: No Built-in Way to Load Policies from Database on Startup #30

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[sushilbansal]

@nomeguy please merge this issue as well :)