diff --git a/Casbin.UnitTests/PersistTests/AdapterTest.cs b/Casbin.UnitTests/PersistTests/AdapterTest.cs
index 784691f..87cb030 100644
--- a/Casbin.UnitTests/PersistTests/AdapterTest.cs
+++ b/Casbin.UnitTests/PersistTests/AdapterTest.cs
@@ -1,5 +1,7 @@
 using System.IO;
 using System.Threading.Tasks;
+using Casbin.Model;
+using Casbin.Persist;
 using Casbin.Persist.Adapter.File;
 using Casbin.Persist.Adapter.Stream;
 using Casbin.Persist.Adapter.Text;
@@ -49,13 +51,54 @@ public async Task TestFileAdapterAsync()
         Assert.True(await e.EnforceAsync("bob", "data2", "write"));
     }
 
+    [Fact]
+    public void TestFilteredFileAdapter()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(e.Enforce("alice", "data1", "read"));
+
+        FileAdapter a = new("Examples/basic_policy.csv");
+        e.SetAdapter(a);
+        e.LoadFilteredPolicy(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(e.Enforce("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(e.Enforce("alice", "data1", "write"));
+        Assert.False(e.Enforce("alice", "data2", "read"));
+        Assert.False(e.Enforce("alice", "data2", "write"));
+        Assert.False(e.Enforce("bob", "data1", "read"));
+        Assert.False(e.Enforce("bob", "data1", "write"));
+        Assert.False(e.Enforce("bob", "data2", "read"));
+        Assert.True(e.Enforce("bob", "data2", "write"));
+    }
+
+    [Fact]
+    public async Task TestFilteredFileAdapterAsync()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(await e.EnforceAsync("alice", "data1", "read"));
+
+        FileAdapter a = new("Examples/basic_policy.csv");
+        e.SetAdapter(a);
+        await e.LoadFilteredPolicyAsync(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(await e.EnforceAsync("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(await e.EnforceAsync("alice", "data1", "write"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "read"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "read"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data2", "read"));
+        Assert.True(await e.EnforceAsync("bob", "data2", "write"));
+    }
+
     [Fact]
     public void TestStreamAdapter()
     {
         Enforcer e = new("Examples/basic_model.conf");
         Assert.False(e.Enforce("alice", "data1", "read"));
 
-        StreamAdapter a = new(File.OpenRead("Examples/basic_policy.csv"));
+        using FileStream stream = File.OpenRead("Examples/basic_policy.csv");
+        StreamAdapter a = new(stream);
         e.SetAdapter(a);
         e.LoadPolicy();
 
@@ -75,7 +118,8 @@ public async Task TestStreamAdapterAsync()
         Enforcer e = new("Examples/basic_model.conf");
         Assert.False(await e.EnforceAsync("alice", "data1", "read"));
 
-        StreamAdapter a = new(File.OpenRead("Examples/basic_policy.csv"));
+        using FileStream stream = File.OpenRead("Examples/basic_policy.csv");
+        StreamAdapter a = new(stream);
         e.SetAdapter(a);
         await e.LoadPolicyAsync();
 
@@ -89,6 +133,48 @@ public async Task TestStreamAdapterAsync()
         Assert.True(await e.EnforceAsync("bob", "data2", "write"));
     }
 
+    [Fact]
+    public void TestFilteredStreamAdapter()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(e.Enforce("alice", "data1", "read"));
+
+        using FileStream stream = File.OpenRead("Examples/basic_policy.csv");
+        StreamAdapter a = new(stream);
+        e.SetAdapter(a);
+        e.LoadFilteredPolicy(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(e.Enforce("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(e.Enforce("alice", "data1", "write"));
+        Assert.False(e.Enforce("alice", "data2", "read"));
+        Assert.False(e.Enforce("alice", "data2", "write"));
+        Assert.False(e.Enforce("bob", "data1", "read"));
+        Assert.False(e.Enforce("bob", "data1", "write"));
+        Assert.False(e.Enforce("bob", "data2", "read"));
+        Assert.True(e.Enforce("bob", "data2", "write"));
+    }
+
+    [Fact]
+    public async Task TestFilteredStreamAdapterAsync()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(await e.EnforceAsync("alice", "data1", "read"));
+
+        using FileStream stream = File.OpenRead("Examples/basic_policy.csv");
+        StreamAdapter a = new(stream);
+        e.SetAdapter(a);
+        await e.LoadFilteredPolicyAsync(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(await e.EnforceAsync("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(await e.EnforceAsync("alice", "data1", "write"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "read"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "read"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data2", "read"));
+        Assert.True(await e.EnforceAsync("bob", "data2", "write"));
+    }
+
     [Fact]
     public void TestTextAdapter()
     {
@@ -132,4 +218,48 @@ public async Task TestTextAdapterAsync()
         Assert.False(await e.EnforceAsync("bob", "data2", "read"));
         Assert.True(await e.EnforceAsync("bob", "data2", "write"));
     }
+
+    [Fact]
+    public void TestFilteredTextAdapter()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(e.Enforce("alice", "data1", "read"));
+
+        TextAdapter a = new(File.ReadAllText("Examples/basic_policy.csv"));
+        e.SetAdapter(a);
+        e.LoadFilteredPolicy(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(e.Enforce("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(e.Enforce("alice", "data1", "write"));
+        Assert.False(e.Enforce("alice", "data2", "read"));
+        Assert.False(e.Enforce("alice", "data2", "write"));
+        Assert.False(e.Enforce("bob", "data1", "read"));
+        Assert.False(e.Enforce("bob", "data1", "write"));
+        Assert.False(e.Enforce("bob", "data2", "read"));
+        Assert.True(e.Enforce("bob", "data2", "write"));
+    }
+
+    [Fact]
+    public async Task TestFilteredTextAdapterAsync()
+    {
+        Enforcer e = new("Examples/basic_model.conf");
+        Assert.False(await e.EnforceAsync("alice", "data1", "read"));
+
+#if NET452 || NET461 || NET462
+        TextAdapter a = new(File.ReadAllText("Examples/basic_policy.csv"));
+#else
+        TextAdapter a = new(await File.ReadAllTextAsync("Examples/basic_policy.csv"));
+#endif
+        e.SetAdapter(a);
+        await e.LoadFilteredPolicyAsync(new PolicyFilter(PermConstants.DefaultPolicyType, 0, Policy.ValuesFrom(["bob"])));
+
+        Assert.False(await e.EnforceAsync("alice", "data1", "read")); // because "alice" is not in the filtered policy
+        Assert.False(await e.EnforceAsync("alice", "data1", "write"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "read"));
+        Assert.False(await e.EnforceAsync("alice", "data2", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "read"));
+        Assert.False(await e.EnforceAsync("bob", "data1", "write"));
+        Assert.False(await e.EnforceAsync("bob", "data2", "read"));
+        Assert.True(await e.EnforceAsync("bob", "data2", "write"));
+    }
 }
diff --git a/Casbin/Persist/PolicyFilter.cs b/Casbin/Persist/PolicyFilter.cs
index 9dad1dd..8a51917 100644
--- a/Casbin/Persist/PolicyFilter.cs
+++ b/Casbin/Persist/PolicyFilter.cs
@@ -4,7 +4,7 @@
 
 namespace Casbin.Persist;
 
-public class PolicyFilter
+public class PolicyFilter : IPolicyFilter
 {
     public static readonly PolicyFilter Empty = new();
     private readonly int _fieldIndex;