Loading filtered policy overwrites previous policies

[seniorquico]

The current PolicyFilter class only supports a single query. If I try to load multiple PolicyFilters, subsequent calls to LoadFilteredPolicy overwrite any previously loaded policies. It's not clear how to load both filtered g and p policies or different sets of p policies from my custom adapter. Is Casbin.NET missing the equivalent to LoadIncrementalFilteredPolicy, or am I thinking about this the wrong way?

https://casbin.org/docs/policy-subset-loading/

[hsluoyz]

@seniorquico can you make a PR?

[seniorquico]

I think I may need some additional guidance on the way to approach this change. In the Go library, I can see the difference between LoadFilteredPolicy and LoadIncrementalFilteredPolicy is simply that the former clears the model's policies and the latter doesn't.

https://github.com/casbin/casbin/blob/1ef00acc917aac9da6b5fdef187fa32e97e8a0bc/enforcer.go#L458-L468

It doesn't appear the extension methods in the C# library are implemented similarly.

Casbin.NET/Casbin/Extensions/Enforcer/EnforcerExtension.cs

Lines 246 to 260 in 999b3f4

	public static async Task<bool> LoadFilteredPolicyAsync(this IEnforcer enforcer, IPolicyFilter filter)
	{
	bool result = await enforcer.Model.LoadFilteredPolicyAsync(filter);
	if (result is false)
	{
	return false;
	}
	if (enforcer.AutoBuildRoleLinks)
	{
	enforcer.BuildRoleLinks();
	}
	return true;
	}

Casbin.NET/Casbin/Extensions/Model/ModelExtension.cs

Lines 126 to 156 in 999b3f4

	public static async Task<bool> LoadFilteredPolicyAsync(this IModel model, IPolicyFilter filter)
	{
	if (model.AdapterHolder.Adapter is null)
	{
	return false;
	}
	if (model.AdapterHolder.FilteredAdapter is null)
	{
	return false;
	}
	DefaultPolicyStore policyStore = new();
	foreach (KeyValuePair<string, PolicyAssertion> pair in model.Sections.GetPolicyAssertions())
	{
	policyStore.AddNode(PermConstants.Section.PolicySection, pair.Key, pair.Value);
	}
	if (model.Sections.ContainsSection(PermConstants.Section.RoleSection))
	{
	foreach (KeyValuePair<string, RoleAssertion> pair in model.Sections.GetRoleAssertions())
	{
	policyStore.AddNode(PermConstants.Section.RoleSection, pair.Key, pair.Value);
	}
	}
	await model.AdapterHolder.FilteredAdapter.LoadFilteredPolicyAsync(policyStore,
	filter);
	model.PolicyStoreHolder.PolicyStore = policyStore;
	return true;
	}

How would you suggest approaching this change?