Add example for adding basic content type filters

src/docs/reference/core/Apis.GraphQL.Abstractions/README.md

@@ -74,12 +74,19 @@ public class Startup : StartupBase
 
 Thats it, your part will now be exposed in GraphQL... just go to the query explorer and take a look. Magic.
 
-### Define a query filter type
+## Filtration
+
+### Define a custom query filter type
 
 So now you have lots of data coming back, the next thing you want to do is to be able to filter said data.
 
 We follow a similar process from step #1, so at this point I will make the assumption you have implemented step #1.
 
+Use this approach if you;
+
+* want to add new filter on Content Type queries
+* need to use custom logic for filtration. For example fetching data from service, comparing complex objects.
+
 What we are going to cover here is;
 
 1. Implement an Input type.
@@ -128,6 +135,7 @@ When an input part is registered, it adds in that part as the parent query, in t
 ```
 
 Next we want to implement a filter. The filter takes the input from the class we just built and the above example, and performs the actual filter against the object passed to it.
+Note that GraphQLFilter also provides PostQueryAsync and can be used also in other usecases as checking permissions etc.
 
 ```csharp
 public class AutoroutePartGraphQLFilter : GraphQLFilter<ContentItem>
@@ -176,6 +184,138 @@ Shown in the example above, we have an autoroutePart argument, this is registere
 
 Done.
 
+### Using default Content Type query filters
+
+In the previous section, we demonstrated how to create filters for complex requirements, allowing you to create custom filtration methods. However, in case you need to add filter on Content Type queries, there is also a simpler solution for many usecases.
+
+Use this approach if you;
+
+* want to add new filter on Content Type queries
+* will have database index with data for your filters
+* you can use simple comparison (equals, contains, in, ...) against index values. For example ```AutoroutePartIndex.path = filterValue```.
+
+We will cover:
+
+1. Implementing a `WhereInputObjectGraphType`.
+2. Implementing `IIndexAliasProvider`.
+3. Registering it in the `Startup` class.
+
+#### Implementing WhereInputObjectGraphType
+
+The `WhereInputObjectGraphType` enhances the `InputObjectGraphType` by introducing methods to define filters such as equality, array filters, etc. This is essential since it's the expected type for the `ContentItemsFieldType` responsible for the filtering logic.
+
+Here is an example implementation:
+
+```csharp
+// Assuming we've added the necessary using directives.
+public class AutorouteInputObjectType : WhereInputObjectGraphType<AutoroutePart>
+{
+    // Binds the filter fields to the GraphQL type representing AutoroutePart
+    public AutorouteInputObjectType()
+    {
+        Name = "AutoroutePartInput";
+
+        // Utilize the method for adding scalar fields from the base class.
+        AddScalarFilterFields<StringGraphType>("path", S["Filter by the path of the content item"]);
+    }
+}
+```
+
+This method will add scalar filters to all ContentItem queries, including custom Content Types.
+
+1. equals, not equals
+2. contains, not contains
+3. starts with, ends with, not starts with, not ends with
+4. in, not in
+
+These filters are checked against an index that is bound to the given ```ContentPart```.
+
+#### Implementing IIndexAliasProvider
+
+To bind ```ContentPart``` to an Index, you have to implement ```IIndexAliasProvider```. Ensure that field names in your filter object are the same as fields in the index. It is needed for filter automatching.
+
+
+```csharp
+public class AutoroutePartIndexAliasProvider : IIndexAliasProvider
+{
+    private static readonly IndexAlias[] _aliases =
+    [
+        new IndexAlias
+        {
+            Alias = "autoroutePart", // alias of graphql ContentPart. You may also use nameof(AutoroutPart).ToFieldName()
+            Index = nameof(AutoroutePartIndex), // name of index bound to part - keep in mind, that fields need to correspond. E.g. 'path' has same name in index and part.
+            IndexType = typeof(AutoroutePartIndex)
+        }
+    ];
+
+    public IEnumerable<IndexAlias> GetAliases()
+    {
+        return _aliases;
+    }
+}
+```
+
+#### Updating the Startup Class
+
+Update Startup class like below.
+
+```csharp
+[RequireFeatures("OrchardCore.Apis.GraphQL")]
+public class Startup : StartupBase
+{
+    // Assuming we've added the necessary using directives.
+    public override void ConfigureServices(IServiceCollection services)
+    {
+        // Code to register the AutoroutePart and AutorouteQueryObjectType is assumed to be present.
+        // Register WhereInputObjectGraphType
+        services.AddInputObjectGraphType<AutoroutePart, AutorouteInputObjectType>();
+
+        // Register IIndexAliasProvider
+        services.AddTransient<IIndexAliasProvider, AutoroutePartIndexAliasProvider>();
+        services.AddWhereInputIndexPropertyProvider<AutoroutePartIndex>();
+    }
+}
+```
+With these configurations, you can navigate to your GraphQL interface, and you should see the new filters available for use in all Content type queries.
+
+#### Example Query Filters
+
+Below are resulting query filters applied to an autoroutePart:
+
+
+```json
+{
+  person(where: {path: {path_contains: "", path: "", path_ends_with: "", path_in: "", path_not: "", path_not_contains: "", path_not_ends_with: "", path_not_in: "", path_not_starts_with: "", path_starts_with: ""}}) {
+    name
+  }
+}
+```
+
+Alternatively, if you register the part with ```collapse = true```, fields will not be nested inside object:
+
+```json
+{
+  person(where: {path_contains: "", path: "", path_ends_with: "", path_in: "", path_not: "", path_not_contains: "", path_not_ends_with: "", path_not_in: "", path_not_starts_with: "", path_starts_with: ""}) {
+    name
+  }
+}
+```
+
+For a more detailed understanding, refer to the implementation of [WhereInputObjectGraphType](https://github.com/OrchardCMS/OrchardCore/blob/main/src/OrchardCore/OrchardCore.Apis.GraphQL.Abstractions/Queries/WhereInputObjectGraphType.cs) and [ContentItemFieldsType](https://github.com/OrchardCMS/OrchardCore/blob/main/src/OrchardCore/OrchardCore.ContentManagement.GraphQL/Queries/ContentItemsFieldType.cs). Also might check the existing index for [`AutoroutePart`](https://github.com/OrchardCMS/OrchardCore/blob/main/src/OrchardCore/OrchardCore.Autoroute.Core/Indexes/AutoroutePartIndex.cs).
+
+### Using arguments for query filtration
+
+There is also possibility to utilize query arguments and use them for filtering query results inside ```Resolve``` method. For more information visit [GraphQL documentation](https://graphql-dotnet.github.io/docs/getting-started/arguments/).
+
+Use this approach if you;
+
+* want to add new filter on any type of query, content part or field
+* will use custom logic for filtration
+
+OrchardCore implementation of filtering query by argument can be seen [in ContentItemQuery](https://github.com/OrchardCMS/OrchardCore/blob/main/src/OrchardCore/OrchardCore.ContentManagement.GraphQL/Queries/ContentItemQuery.cs) or ```MediaAssetQuery```.
+
+OrchardCore implementation of applying argument on field can be seen in ```MediaFieldQueryObjectType```.
+
 ## Querying related content items
 
 One of the features of Content Items, is that they can be related to other Content Items.