fix query database under wiki page

Src/Notion.Client/Models/Database/IDatabaseParent.cs

@@ -7,6 +7,7 @@ namespace Notion.Client
     [JsonSubtypes.KnownSubTypeAttribute(typeof(PageParent), ParentType.PageId)]
     [JsonSubtypes.KnownSubTypeAttribute(typeof(WorkspaceParent), ParentType.Workspace)]
     [JsonSubtypes.KnownSubTypeAttribute(typeof(BlockParent), ParentType.BlockId)]
+    [JsonSubtypes.KnownSubTypeAttribute(typeof(DatabaseParent), ParentType.DatabaseId)]
     public interface IDatabaseParent : IParent
     {
     }

Src/Notion.Client/Models/Parents/DatabaseParent.cs

@@ -2,7 +2,7 @@
 
 namespace Notion.Client
 {
-    public class DatabaseParent : IPageParent, IBlockParent
+    public class DatabaseParent : IPageParent, IBlockParent, IDatabaseParent
     {
         /// <summary>
         ///     The ID of the database that this page belongs to.

Test/Notion.UnitTests/DatabasesClientTests.cs

@@ -518,4 +518,28 @@ public async Task RetrieveAsync_throws_argument_null_exception_if_database_id_is
         var exception = await Assert.ThrowsAsync<ArgumentNullException>(Act);
         Assert.Equal("databaseId", exception.ParamName);
     }
+
+    [Fact]
+    public async Task RetrieveWikiParentDatabaseAsync()
+    {
+        var databaseId = "7g82e3a3-2c13-07e8-h7d9-d36cab1fd6f9";
+        var path = ApiEndpoints.DatabasesApiUrls.Retrieve(databaseId);
+        var jsonData = await File.ReadAllTextAsync("data/databases/WikiParentDatabaseRetrieveResponse.json");
+
+        Server.Given(CreateGetRequestBuilder(path))
+            .RespondWith(
+                Response.Create()
+                    .WithStatusCode(200)
+                    .WithBody(jsonData)
+            );
+
+        var database = await _client.RetrieveAsync(databaseId);
+
+        // Verify that when the parent is a database (such as a Wiki page), parent.type becomes database_id
+        database.Parent.Type.Should().Be(ParentType.DatabaseId);
+        database.Parent.Should().BeOfType<DatabaseParent>();
+        ((DatabaseParent)database.Parent).DatabaseId.Should().Be("6a82a3a3-9c10-802c-9c8a-de6564be71fm");
+        database.Title.Should().ContainSingle();
+        database.Title[0].PlainText.Should().Be("Database within Wiki page");
+    }
 }

Test/Notion.UnitTests/Notion.UnitTests.csproj

@@ -52,6 +52,9 @@
     <None Update="data\databases\UpdateDatabaseResponse.json">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="data\databases\WikiParentDatabaseRetrieveResponse.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="data\pages\TrashPageResponse.json">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>

Test/Notion.UnitTests/data/databases/WikiParentDatabaseRetrieveResponse.json

@@ -0,0 +1,69 @@
+{
+    "object": "database",
+    "id": "7g82e3a3-2c13-07e8-h7d9-d36cab1fd6f9",
+    "cover": null,
+    "icon": null,
+    "created_time": "2025-11-11T09:29:00.000Z",
+    "created_by": {
+        "object": "user",
+        "id": "641217ad-5167-4955-a206-f512e67214k7"
+    },
+    "last_edited_by": {
+        "object": "user",
+        "id": "641217ad-5167-4955-a206-f512e67214k7"
+    },
+    "last_edited_time": "2025-11-20T02:27:00.000Z",
+    "title": [
+        {
+            "type": "text",
+            "text": {
+                "content": "Database within Wiki page",
+                "link": null
+            },
+            "annotations": {
+                "bold": false,
+                "italic": false,
+                "strikethrough": false,
+                "underline": false,
+                "code": false,
+                "color": "default"
+            },
+            "plain_text": "Database within Wiki page",
+            "href": null
+        }
+    ],
+    "description": [],
+    "is_inline": true,
+    "properties": {
+        "Text": {
+            "id": "N%5EPy",
+            "name": "Text",
+            "description": null,
+            "type": "rich_text",
+            "rich_text": {}
+        },
+        "Date": {
+            "id": "%5EE_%5C",
+            "name": "Date",
+            "description": null,
+            "type": "date",
+            "date": {}
+        },
+        "Name": {
+            "id": "title",
+            "name": "Name",
+            "description": null,
+            "type": "title",
+            "title": {}
+        }
+    },
+    "parent": {
+        "type": "database_id",
+        "database_id": "6a82a3a3-9c10-802c-9c8a-de6564be71fm"
+    },
+    "url": "https://www.notion.so/4f6ff1bac6d9d1a8e0831c93a3e28a2",
+    "public_url": null,
+    "archived": false,
+    "in_trash": false,
+    "request_id": "f1e6eg7c-8c27-4fc3-fab6-da6f311d1zh9"
+}