diff --git a/README.md b/README.md
index e645d8b..a5e69f6 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ dotnet add package JsonApiDotNetCore.MongoDb
 #nullable enable
 
 [Resource]
-public class Book : MongoIdentifiable
+public class Book : HexStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
@@ -70,9 +70,19 @@ builder.Services.AddJsonApiMongoDb();
 builder.Services.AddScoped(typeof(IResourceReadRepository<,>), typeof(MongoRepository<,>));
 builder.Services.AddScoped(typeof(IResourceWriteRepository<,>), typeof(MongoRepository<,>));
 builder.Services.AddScoped(typeof(IResourceRepository<,>), typeof(MongoRepository<,>));
-
 ```
 
+## Using client-generated IDs
+Resources that inherit from `HexStringMongoIdentifiable` use auto-generated (performant) 12-byte hexadecimal
+[Object IDs](https://docs.mongodb.com/manual/reference/bson-types/#objectid).
+You can assign an ID manually, but it must match the 12-byte hexadecimal pattern.
+
+To assign free-format string IDs manually, make your resources inherit from `FreeStringMongoIdentifiable` instead.
+When creating a resource without assigning an ID, a 12-byte hexadecimal ID will be auto-generated.
+
+Set `options.AllowClientGeneratedIds` to `true` in Program.cs to allow API clients to assign IDs. This can be combined
+with both base classes, but `FreeStringMongoIdentifiable` probably makes the most sense.
+
 ## Limitations
 
 - JSON:API relationships are currently not supported. You can use complex object graphs though, which are stored in a single document.
diff --git a/src/Examples/GettingStarted/Models/Book.cs b/src/Examples/GettingStarted/Models/Book.cs
index b9853d1..49310bd 100644
--- a/src/Examples/GettingStarted/Models/Book.cs
+++ b/src/Examples/GettingStarted/Models/Book.cs
@@ -6,7 +6,7 @@ namespace GettingStarted.Models;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource]
-public sealed class Book : MongoIdentifiable
+public sealed class Book : HexStringMongoIdentifiable
 {
     [Attr]
     public string Title { get; set; } = null!;
diff --git a/src/Examples/JsonApiDotNetCoreMongoDbExample/Models/TodoItem.cs b/src/Examples/JsonApiDotNetCoreMongoDbExample/Models/TodoItem.cs
index e2adddd..7dc654c 100644
--- a/src/Examples/JsonApiDotNetCoreMongoDbExample/Models/TodoItem.cs
+++ b/src/Examples/JsonApiDotNetCoreMongoDbExample/Models/TodoItem.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbExample.Models;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource]
-public sealed class TodoItem : MongoIdentifiable
+public sealed class TodoItem : HexStringMongoIdentifiable
 {
     [Attr]
     public string Description { get; set; } = null!;
diff --git a/src/JsonApiDotNetCore.MongoDb/Queries/Internal/HideRelationshipsSparseFieldSetCache.cs b/src/JsonApiDotNetCore.MongoDb/Queries/Internal/HideRelationshipsSparseFieldSetCache.cs
index 414b5f7..be71664 100644
--- a/src/JsonApiDotNetCore.MongoDb/Queries/Internal/HideRelationshipsSparseFieldSetCache.cs
+++ b/src/JsonApiDotNetCore.MongoDb/Queries/Internal/HideRelationshipsSparseFieldSetCache.cs
@@ -1,5 +1,6 @@
 using System.Collections.Immutable;
 using JsonApiDotNetCore.Configuration;
+using JsonApiDotNetCore.MongoDb.Resources;
 using JsonApiDotNetCore.Queries;
 using JsonApiDotNetCore.Queries.Internal;
 using JsonApiDotNetCore.Resources;
@@ -38,6 +39,11 @@ public IImmutableSet<ResourceFieldAttribute> GetSparseFieldSetForSerializer(Reso
     {
         IImmutableSet<ResourceFieldAttribute> fieldSet = _innerCache.GetSparseFieldSetForSerializer(resourceType);
 
+        return resourceType.ClrType.IsAssignableTo(typeof(IMongoIdentifiable)) ? RemoveRelationships(fieldSet) : fieldSet;
+    }
+
+    private static IImmutableSet<ResourceFieldAttribute> RemoveRelationships(IImmutableSet<ResourceFieldAttribute> fieldSet)
+    {
         ResourceFieldAttribute[] relationships = fieldSet.Where(field => field is RelationshipAttribute).ToArray();
         return fieldSet.Except(relationships);
     }
diff --git a/src/JsonApiDotNetCore.MongoDb/Repositories/MongoRepository.cs b/src/JsonApiDotNetCore.MongoDb/Repositories/MongoRepository.cs
index 07a6030..de3d9e0 100644
--- a/src/JsonApiDotNetCore.MongoDb/Repositories/MongoRepository.cs
+++ b/src/JsonApiDotNetCore.MongoDb/Repositories/MongoRepository.cs
@@ -5,6 +5,7 @@
 using JsonApiDotNetCore.Middleware;
 using JsonApiDotNetCore.MongoDb.Errors;
 using JsonApiDotNetCore.MongoDb.Queries.Internal.QueryableBuilding;
+using JsonApiDotNetCore.MongoDb.Resources;
 using JsonApiDotNetCore.Queries;
 using JsonApiDotNetCore.Queries.Expressions;
 using JsonApiDotNetCore.Queries.Internal.QueryableBuilding;
@@ -52,9 +53,9 @@ public MongoRepository(IMongoDataAccess mongoDataAccess, ITargetedFields targete
         _constraintProviders = constraintProviders;
         _resourceDefinitionAccessor = resourceDefinitionAccessor;
 
-        if (typeof(TId) != typeof(string))
+        if (!typeof(TResource).IsAssignableTo(typeof(IMongoIdentifiable)))
         {
-            throw new InvalidConfigurationException("MongoDB can only be used for resources with an 'Id' property of type 'string'.");
+            throw new InvalidConfigurationException("MongoDB can only be used with resources that implement 'IMongoIdentifiable'.");
         }
     }
 
diff --git a/src/JsonApiDotNetCore.MongoDb/Resources/FreeStringMongoIdentifiable.cs b/src/JsonApiDotNetCore.MongoDb/Resources/FreeStringMongoIdentifiable.cs
new file mode 100644
index 0000000..ca19d2e
--- /dev/null
+++ b/src/JsonApiDotNetCore.MongoDb/Resources/FreeStringMongoIdentifiable.cs
@@ -0,0 +1,27 @@
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Bson.Serialization.IdGenerators;
+
+namespace JsonApiDotNetCore.MongoDb.Resources;
+
+/// <summary>
+/// Basic implementation of a JSON:API resource whose Id is stored as a free-format string in MongoDB. Useful for resources that are created using
+/// client-generated IDs.
+/// </summary>
+public abstract class FreeStringMongoIdentifiable : IMongoIdentifiable
+{
+    /// <inheritdoc />
+    [BsonId(IdGenerator = typeof(StringObjectIdGenerator))]
+    public virtual string? Id { get; set; }
+
+    /// <inheritdoc />
+    [BsonIgnore]
+    public string? StringId
+    {
+        get => Id;
+        set => Id = value;
+    }
+
+    /// <inheritdoc />
+    [BsonIgnore]
+    public string? LocalId { get; set; }
+}
diff --git a/src/JsonApiDotNetCore.MongoDb/Resources/MongoIdentifiable.cs b/src/JsonApiDotNetCore.MongoDb/Resources/HexStringMongoIdentifiable.cs
similarity index 70%
rename from src/JsonApiDotNetCore.MongoDb/Resources/MongoIdentifiable.cs
rename to src/JsonApiDotNetCore.MongoDb/Resources/HexStringMongoIdentifiable.cs
index b8b4104..e4049f9 100644
--- a/src/JsonApiDotNetCore.MongoDb/Resources/MongoIdentifiable.cs
+++ b/src/JsonApiDotNetCore.MongoDb/Resources/HexStringMongoIdentifiable.cs
@@ -1,13 +1,12 @@
-using JsonApiDotNetCore.Resources;
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization.Attributes;
 
 namespace JsonApiDotNetCore.MongoDb.Resources;
 
 /// <summary>
-/// A convenient basic implementation of <see cref="IIdentifiable" /> for use with MongoDB models.
+/// Basic implementation of a JSON:API resource whose Id is stored as a 12-byte hexadecimal ObjectId in MongoDB.
 /// </summary>
-public abstract class MongoIdentifiable : IIdentifiable<string?>
+public abstract class HexStringMongoIdentifiable : IMongoIdentifiable
 {
     /// <inheritdoc />
     [BsonId]
diff --git a/src/JsonApiDotNetCore.MongoDb/Resources/IMongoIdentifiable.cs b/src/JsonApiDotNetCore.MongoDb/Resources/IMongoIdentifiable.cs
new file mode 100644
index 0000000..11dbfa2
--- /dev/null
+++ b/src/JsonApiDotNetCore.MongoDb/Resources/IMongoIdentifiable.cs
@@ -0,0 +1,10 @@
+using JsonApiDotNetCore.Resources;
+
+namespace JsonApiDotNetCore.MongoDb.Resources;
+
+/// <summary>
+/// Marker interface to indicate a resource that is stored in MongoDB.
+/// </summary>
+public interface IMongoIdentifiable : IIdentifiable<string?>
+{
+}
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceWithClientGeneratedIdTests.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceWithClientGeneratedIdTests.cs
index f0671b3..40ebec1 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceWithClientGeneratedIdTests.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceWithClientGeneratedIdTests.cs
@@ -3,7 +3,6 @@
 using JsonApiDotNetCore.Configuration;
 using JsonApiDotNetCore.Serialization.Objects;
 using Microsoft.Extensions.DependencyInjection;
-using MongoDB.Bson;
 using TestBuildingBlocks;
 using Xunit;
 
@@ -28,7 +27,7 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_sid
     {
         // Arrange
         TextLanguage newLanguage = _fakers.TextLanguage.Generate();
-        newLanguage.Id = ObjectId.GenerateNewId().ToString();
+        newLanguage.Id = "free-format-client-generated-id";
 
         var requestBody = new
         {
@@ -82,8 +81,8 @@ await _testContext.RunOnDatabaseAsync(async dbContext =>
     public async Task Can_create_resource_with_client_generated_string_ID_having_no_side_effects()
     {
         // Arrange
-        MusicTrack newTrack = _fakers.MusicTrack.Generate();
-        newTrack.Id = ObjectId.GenerateNewId().ToString();
+        Playlist newPlaylist = _fakers.Playlist.Generate();
+        newPlaylist.Id = "free-format-client-generated-id";
 
         var requestBody = new
         {
@@ -94,13 +93,11 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_no_
                     op = "add",
                     data = new
                     {
-                        type = "musicTracks",
-                        id = newTrack.StringId,
+                        type = "playlists",
+                        id = newPlaylist.StringId,
                         attributes = new
                         {
-                            title = newTrack.Title,
-                            lengthInSeconds = newTrack.LengthInSeconds,
-                            releasedAt = newTrack.ReleasedAt
+                            name = newPlaylist.Name
                         }
                     }
                 }
@@ -119,10 +116,9 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_no_
 
         await _testContext.RunOnDatabaseAsync(async dbContext =>
         {
-            MusicTrack trackInDatabase = await dbContext.MusicTracks.FirstWithIdAsync(newTrack.Id);
+            Playlist playlistInDatabase = await dbContext.Playlists.FirstWithIdAsync(newPlaylist.Id);
 
-            trackInDatabase.Title.Should().Be(newTrack.Title);
-            trackInDatabase.LengthInSeconds.Should().BeApproximately(newTrack.LengthInSeconds);
+            playlistInDatabase.Name.Should().Be(newPlaylist.Name);
         });
     }
 
@@ -131,7 +127,7 @@ public async Task Cannot_create_resource_for_existing_client_generated_ID()
     {
         // Arrange
         TextLanguage existingLanguage = _fakers.TextLanguage.Generate();
-        existingLanguage.Id = ObjectId.GenerateNewId().ToString();
+        existingLanguage.Id = "existing-free-format-client-generated-id";
 
         string newIsoCode = _fakers.TextLanguage.Generate().IsoCode!;
 
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Lyric.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Lyric.cs
index 3618a77..674e682 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Lyric.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Lyric.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class Lyric : MongoIdentifiable
+public sealed class Lyric : HexStringMongoIdentifiable
 {
     [Attr]
     public string? Format { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/MusicTrack.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/MusicTrack.cs
index 2f0fb01..2db3dfa 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/MusicTrack.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/MusicTrack.cs
@@ -8,7 +8,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class MusicTrack : MongoIdentifiable
+public sealed class MusicTrack : HexStringMongoIdentifiable
 {
     [RegularExpression(@"^[a-fA-F\d]{24}$")]
     public override string? Id { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Performer.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Performer.cs
index 346b7a3..5087bfd 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Performer.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Performer.cs
@@ -6,7 +6,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class Performer : MongoIdentifiable
+public sealed class Performer : HexStringMongoIdentifiable
 {
     [Attr]
     public string? ArtistName { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Playlist.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Playlist.cs
index ea1d8af..876fe36 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Playlist.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/Playlist.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class Playlist : MongoIdentifiable
+public sealed class Playlist : FreeStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/RecordCompany.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/RecordCompany.cs
index b50ff94..761c1e1 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/RecordCompany.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/RecordCompany.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class RecordCompany : MongoIdentifiable
+public sealed class RecordCompany : HexStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/TextLanguage.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/TextLanguage.cs
index 8c621b8..08a3d4f 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/TextLanguage.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/AtomicOperations/TextLanguage.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.AtomicOperations")]
-public sealed class TextLanguage : MongoIdentifiable
+public sealed class TextLanguage : FreeStringMongoIdentifiable
 {
     [Attr]
     public string? IsoCode { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/Meta/SupportTicket.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/Meta/SupportTicket.cs
index e382405..098de4e 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/Meta/SupportTicket.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/Meta/SupportTicket.cs
@@ -6,7 +6,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.Meta;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.Meta")]
-public sealed class SupportTicket : MongoIdentifiable
+public sealed class SupportTicket : HexStringMongoIdentifiable
 {
     [Attr]
     public string Description { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/AccountPreferences.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/AccountPreferences.cs
index f4b3858..0cd5aa2 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/AccountPreferences.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/AccountPreferences.cs
@@ -5,7 +5,7 @@
 namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
-public sealed class AccountPreferences : MongoIdentifiable
+public sealed class AccountPreferences : HexStringMongoIdentifiable
 {
     [Attr]
     public bool UseDarkTheme { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Blog.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Blog.cs
index 93dfabc..bc0530f 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Blog.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Blog.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings")]
-public sealed class Blog : MongoIdentifiable
+public sealed class Blog : HexStringMongoIdentifiable
 {
     [Attr]
     public string Title { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/BlogPost.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/BlogPost.cs
index 85d366e..4508e2f 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/BlogPost.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/BlogPost.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings")]
-public sealed class BlogPost : MongoIdentifiable
+public sealed class BlogPost : HexStringMongoIdentifiable
 {
     [Attr]
     public string Caption { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Comment.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Comment.cs
index 6c79972..38a3ebd 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Comment.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Comment.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings")]
-public sealed class Comment : MongoIdentifiable
+public sealed class Comment : HexStringMongoIdentifiable
 {
     [Attr]
     public string Text { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Filtering/FilterableResource.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Filtering/FilterableResource.cs
index c82fcd9..e474854 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Filtering/FilterableResource.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Filtering/FilterableResource.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings.Filtering;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings.Filtering")]
-public sealed class FilterableResource : MongoIdentifiable
+public sealed class FilterableResource : HexStringMongoIdentifiable
 {
     [Attr]
     public string SomeString { get; set; } = string.Empty;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Label.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Label.cs
index 9c29c87..5c267fb 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Label.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/Label.cs
@@ -6,7 +6,7 @@
 namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
-public sealed class Label : MongoIdentifiable
+public sealed class Label : HexStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/LoginAttempt.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/LoginAttempt.cs
index 51bbf50..5e06cea 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/LoginAttempt.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/LoginAttempt.cs
@@ -5,7 +5,7 @@
 namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
-public sealed class LoginAttempt : MongoIdentifiable
+public sealed class LoginAttempt : HexStringMongoIdentifiable
 {
     [Attr]
     public DateTimeOffset TriedAt { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/WebAccount.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/WebAccount.cs
index 28f59c3..de3c673 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/WebAccount.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/QueryStrings/WebAccount.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.QueryStrings")]
-public sealed class WebAccount : MongoIdentifiable
+public sealed class WebAccount : HexStringMongoIdentifiable
 {
     [Attr]
     public string UserName { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceTests.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceTests.cs
index fdc80bf..35c873f 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceTests.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceTests.cs
@@ -98,7 +98,7 @@ public async Task Cannot_create_resource_with_int_ID()
         ErrorObject error = responseDocument.Errors[0];
         error.StatusCode.Should().Be(HttpStatusCode.InternalServerError);
         error.Title.Should().Be("An unhandled error occurred while processing this request.");
-        error.Detail.Should().Be("MongoDB can only be used for resources with an 'Id' property of type 'string'.");
+        error.Detail.Should().Be("MongoDB can only be used with resources that implement 'IMongoIdentifiable'.");
     }
 
     [Fact]
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceWithClientGeneratedIdTests.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceWithClientGeneratedIdTests.cs
index 2fb07c0..e22f6cf 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceWithClientGeneratedIdTests.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/Creating/CreateResourceWithClientGeneratedIdTests.cs
@@ -3,7 +3,6 @@
 using JsonApiDotNetCore.Configuration;
 using JsonApiDotNetCore.Serialization.Objects;
 using Microsoft.Extensions.DependencyInjection;
-using MongoDB.Bson;
 using TestBuildingBlocks;
 using Xunit;
 
@@ -35,7 +34,7 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_sid
     {
         // Arrange
         WorkItemGroup newGroup = _fakers.WorkItemGroup.Generate();
-        newGroup.Id = ObjectId.GenerateNewId().ToString();
+        newGroup.Id = "free-format-client-generated-id-1";
 
         var requestBody = new
         {
@@ -79,7 +78,7 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_sid
     {
         // Arrange
         WorkItemGroup newGroup = _fakers.WorkItemGroup.Generate();
-        newGroup.Id = ObjectId.GenerateNewId().ToString();
+        newGroup.Id = "free-format-client-generated-id-2";
 
         var requestBody = new
         {
@@ -124,7 +123,7 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_no_
     {
         // Arrange
         RgbColor newColor = _fakers.RgbColor.Generate();
-        newColor.Id = ObjectId.GenerateNewId().ToString();
+        newColor.Id = "free-format-client-generated-id-3";
 
         var requestBody = new
         {
@@ -162,7 +161,7 @@ public async Task Can_create_resource_with_client_generated_string_ID_having_no_
     {
         // Arrange
         RgbColor newColor = _fakers.RgbColor.Generate();
-        newColor.Id = ObjectId.GenerateNewId().ToString();
+        newColor.Id = "free-format-client-generated-id-4";
 
         var requestBody = new
         {
@@ -200,7 +199,7 @@ public async Task Cannot_create_resource_for_existing_client_generated_ID()
     {
         // Arrange
         RgbColor existingColor = _fakers.RgbColor.Generate();
-        existingColor.Id = ObjectId.GenerateNewId().ToString();
+        existingColor.Id = "free-format-client-generated-id-5";
 
         string newDisplayName = _fakers.RgbColor.Generate().DisplayName;
 
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/RgbColor.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/RgbColor.cs
index 7d95c46..a86f1c2 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/RgbColor.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/RgbColor.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite")]
-public sealed class RgbColor : MongoIdentifiable
+public sealed class RgbColor : FreeStringMongoIdentifiable
 {
     [Attr]
     public string DisplayName { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/UserAccount.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/UserAccount.cs
index a024856..53ae918 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/UserAccount.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/UserAccount.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite")]
-public sealed class UserAccount : MongoIdentifiable
+public sealed class UserAccount : HexStringMongoIdentifiable
 {
     [Attr]
     public string FirstName { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItem.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItem.cs
index 925ed77..4eecb06 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItem.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItem.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite")]
-public sealed class WorkItem : MongoIdentifiable
+public sealed class WorkItem : HexStringMongoIdentifiable
 {
     [Attr]
     public string? Description { get; set; }
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItemGroup.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItemGroup.cs
index f46a306..6dd08e4 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItemGroup.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkItemGroup.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite")]
-public sealed class WorkItemGroup : MongoIdentifiable
+public sealed class WorkItemGroup : FreeStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkTag.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkTag.cs
index 01a061d..48de6cf 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkTag.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ReadWrite/WorkTag.cs
@@ -6,7 +6,7 @@
 namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
-public sealed class WorkTag : MongoIdentifiable
+public sealed class WorkTag : HexStringMongoIdentifiable
 {
     [Attr]
     public string Text { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Moon.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Moon.cs
index bf5615f..603a755 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Moon.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Moon.cs
@@ -6,7 +6,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Rea
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Reading")]
-public sealed class Moon : MongoIdentifiable
+public sealed class Moon : HexStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Planet.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Planet.cs
index f84d013..6b94174 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Planet.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Planet.cs
@@ -7,7 +7,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Rea
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Reading")]
-public sealed class Planet : MongoIdentifiable
+public sealed class Planet : HexStringMongoIdentifiable
 {
     [Attr]
     public string PublicName { get; set; } = null!;
diff --git a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Star.cs b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Star.cs
index 3c30784..12ede8b 100644
--- a/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Star.cs
+++ b/test/JsonApiDotNetCoreMongoDbTests/IntegrationTests/ResourceDefinitions/Reading/Star.cs
@@ -6,7 +6,7 @@ namespace JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Rea
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
 [Resource(ControllerNamespace = "JsonApiDotNetCoreMongoDbTests.IntegrationTests.ResourceDefinitions.Reading")]
-public sealed class Star : MongoIdentifiable
+public sealed class Star : HexStringMongoIdentifiable
 {
     [Attr]
     public string Name { get; set; } = null!;
diff --git a/test/TestBuildingBlocks/MongoDbContextShim.cs b/test/TestBuildingBlocks/MongoDbContextShim.cs
index 9c07d9f..323af40 100644
--- a/test/TestBuildingBlocks/MongoDbContextShim.cs
+++ b/test/TestBuildingBlocks/MongoDbContextShim.cs
@@ -18,7 +18,7 @@ protected MongoDbContextShim(IMongoDatabase database)
     }
 
     protected MongoDbSetShim<TEntity> Set<TEntity>()
-        where TEntity : MongoIdentifiable
+        where TEntity : IMongoIdentifiable
     {
         IMongoCollection<TEntity> collection = _database.GetCollection<TEntity>(typeof(TEntity).Name);
         var dbSetShim = new MongoDbSetShim<TEntity>(collection);
@@ -28,7 +28,7 @@ protected MongoDbSetShim<TEntity> Set<TEntity>()
     }
 
     public async Task ClearTableAsync<TEntity>()
-        where TEntity : MongoIdentifiable
+        where TEntity : IMongoIdentifiable
     {
         await _database.DropCollectionAsync(typeof(TEntity).Name);
     }
diff --git a/test/TestBuildingBlocks/MongoDbSetShim.cs b/test/TestBuildingBlocks/MongoDbSetShim.cs
index af1bf8e..7e58223 100644
--- a/test/TestBuildingBlocks/MongoDbSetShim.cs
+++ b/test/TestBuildingBlocks/MongoDbSetShim.cs
@@ -15,7 +15,7 @@ public abstract class MongoDbSetShim
 /// repository.
 /// </summary>
 public sealed class MongoDbSetShim<TEntity> : MongoDbSetShim
-    where TEntity : MongoIdentifiable
+    where TEntity : IMongoIdentifiable
 {
     private readonly IMongoCollection<TEntity> _collection;
     private readonly List<TEntity> _entitiesToInsert = new();
@@ -64,21 +64,19 @@ public async Task ExecuteAsync(Func<IMongoCollection<TEntity>, Task> action)
 
     public async Task<TEntity> FirstWithIdAsync(string? id, CancellationToken cancellationToken = default)
     {
-        MongoIdentifiable? firstOrDefault = await _collection.AsQueryable().FirstOrDefaultAsync(document => Equals(document.Id, id), cancellationToken);
+        TEntity entity = await _collection.AsQueryable().FirstOrDefaultAsync(document => Equals(document.Id, id), cancellationToken);
 
-        if (Equals(firstOrDefault, default(MongoIdentifiable)))
+        if (entity is null)
         {
             throw new InvalidOperationException($"Resource with ID '{id}' was not found.");
         }
 
-        return (TEntity)firstOrDefault;
+        return entity;
     }
 
     public async Task<TEntity?> FirstWithIdOrDefaultAsync(string? id, CancellationToken cancellationToken = default)
     {
-        MongoIdentifiable? entity = await _collection.AsQueryable().FirstOrDefaultAsync(document => Equals(document.Id, id), cancellationToken);
-
-        return (TEntity?)entity;
+        return await _collection.AsQueryable().FirstOrDefaultAsync(document => Equals(document.Id, id), cancellationToken);
     }
 
     public async Task<List<TEntity>> ToListAsync(CancellationToken cancellationToken = default)