Fixed: Do not allow the use of 'lid' when client-generated IDs are required

src/JsonApiDotNetCore/Serialization/Request/Adapters/AtomicOperationObjectAdapter.cs

@@ -125,7 +125,9 @@ private ResourceIdentityRequirements CreateRefRequirements(RequestAdapterState s
         return new ResourceIdentityRequirements
         {
             EvaluateIdConstraint = resourceType =>
-                ResourceIdentityRequirements.DoEvaluateIdConstraint(resourceType, state.Request.WriteOperation, _options.ClientIdGeneration)
+                ResourceIdentityRequirements.DoEvaluateIdConstraint(resourceType, state.Request.WriteOperation, _options.ClientIdGeneration),
+            EvaluateAllowLid = resourceType =>
+                ResourceIdentityRequirements.DoEvaluateAllowLid(resourceType, state.Request.WriteOperation, _options.ClientIdGeneration)
         };
     }
 
@@ -135,6 +137,7 @@ private static ResourceIdentityRequirements CreateDataRequirements(AtomicReferen
         {
             ResourceType = refResult.ResourceType,
             EvaluateIdConstraint = refRequirements.EvaluateIdConstraint,
+            EvaluateAllowLid = refRequirements.EvaluateAllowLid,
             IdValue = refResult.Resource.StringId,
             LidValue = refResult.Resource.LocalId,
             RelationshipName = refResult.Relationship?.PublicName

src/JsonApiDotNetCore/Serialization/Request/Adapters/RelationshipDataAdapter.cs

@@ -1,4 +1,5 @@
 using System.Collections;
+using JsonApiDotNetCore.Middleware;
 using JsonApiDotNetCore.Resources;
 using JsonApiDotNetCore.Resources.Annotations;
 using JsonApiDotNetCore.Serialization.Objects;
@@ -71,6 +72,7 @@ private static SingleOrManyData<ResourceIdentifierObject> ToIdentifierData(Singl
         {
             ResourceType = relationship.RightType,
             EvaluateIdConstraint = _ => JsonElementConstraint.Required,
+            EvaluateAllowLid = _ => state.Request.Kind == EndpointKind.AtomicOperations,
             RelationshipName = relationship.PublicName
         };
 

src/JsonApiDotNetCore/Serialization/Request/Adapters/ResourceIdentityAdapter.cs

@@ -96,18 +96,20 @@ private static void AssertIsCompatibleResourceType(ResourceType actual, Resource
     private IIdentifiable CreateResource(ResourceIdentity identity, ResourceIdentityRequirements requirements, ResourceType resourceType,
         RequestAdapterState state)
     {
-        if (state.Request.Kind != EndpointKind.AtomicOperations)
+        AssertNoIdWithLid(identity, state);
+
+        bool allowLid = requirements.EvaluateAllowLid?.Invoke(resourceType) ?? false;
+
+        if (!allowLid)
         {
             AssertHasNoLid(identity, state);
         }
 
-        AssertNoIdWithLid(identity, state);
-
         JsonElementConstraint? idConstraint = requirements.EvaluateIdConstraint?.Invoke(resourceType);
 
         if (idConstraint == JsonElementConstraint.Required)
         {
-            AssertHasIdOrLid(identity, requirements, state);
+            AssertHasIdOrLid(identity, requirements, allowLid, state);
         }
         else if (idConstraint == JsonElementConstraint.Forbidden)
         {
@@ -128,7 +130,10 @@ private static void AssertHasNoLid(ResourceIdentity identity, RequestAdapterStat
         if (identity.Lid != null)
         {
             using IDisposable _ = state.Position.PushElement("lid");
-            throw new ModelConversionException(state.Position, "The 'lid' element is not supported at this endpoint.", null);
+
+            throw state.Request.Kind == EndpointKind.AtomicOperations
+                ? new ModelConversionException(state.Position, "The 'lid' element cannot be used because a client-generated ID is required.", null)
+                : new ModelConversionException(state.Position, "The 'lid' element is not supported at this endpoint.", null);
         }
     }
 
@@ -140,7 +145,7 @@ private static void AssertNoIdWithLid(ResourceIdentity identity, RequestAdapterS
         }
     }
 
-    private static void AssertHasIdOrLid(ResourceIdentity identity, ResourceIdentityRequirements requirements, RequestAdapterState state)
+    private static void AssertHasIdOrLid(ResourceIdentity identity, ResourceIdentityRequirements requirements, bool allowLid, RequestAdapterState state)
     {
         string? message = null;
 
@@ -154,7 +159,7 @@ private static void AssertHasIdOrLid(ResourceIdentity identity, ResourceIdentity
         }
         else if (identity.Id == null && identity.Lid == null)
         {
-            message = state.Request.Kind == EndpointKind.AtomicOperations ? "The 'id' or 'lid' element is required." : "The 'id' element is required.";
+            message = allowLid ? "The 'id' or 'lid' element is required." : "The 'id' element is required.";
         }
 
         if (message != null)

src/JsonApiDotNetCore/Serialization/Request/Adapters/ResourceIdentityRequirements.cs

@@ -21,6 +21,11 @@ public sealed class ResourceIdentityRequirements
     /// </summary>
     public Func<ResourceType, JsonElementConstraint?>? EvaluateIdConstraint { get; init; }
 
+    /// <summary>
+    /// When not null, provides a callback to indicate whether the "lid" element can be used instead of the "id" element. Defaults to <c>false</c>.
+    /// </summary>
+    public Func<ResourceType, bool>? EvaluateAllowLid { get; init; }
+
     /// <summary>
     /// When not null, indicates what the value of the "id" element must be.
     /// </summary>
@@ -50,4 +55,15 @@ public sealed class ResourceIdentityRequirements
             }
             : JsonElementConstraint.Required;
     }
+
+    internal static bool DoEvaluateAllowLid(ResourceType resourceType, WriteOperationKind? writeOperation, ClientIdGenerationMode globalClientIdGeneration)
+    {
+        if (writeOperation == null)
+        {
+            return false;
+        }
+
+        ClientIdGenerationMode clientIdGeneration = resourceType.ClientIdGeneration ?? globalClientIdGeneration;
+        return !(writeOperation == WriteOperationKind.CreateResource && clientIdGeneration == ClientIdGenerationMode.Required);
+    }
 }

test/JsonApiDotNetCoreTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceWithClientGeneratedIdTests.cs

@@ -175,7 +175,7 @@ public async Task Cannot_create_resource_for_missing_client_generated_ID()
 
         ErrorObject error = responseDocument.Errors[0];
         error.StatusCode.Should().Be(HttpStatusCode.UnprocessableEntity);
-        error.Title.Should().Be("Failed to deserialize request body: The 'id' or 'lid' element is required.");
+        error.Title.Should().Be("Failed to deserialize request body: The 'id' element is required.");
         error.Detail.Should().BeNull();
         error.Source.ShouldNotBeNull();
         error.Source.Pointer.Should().Be("/atomic:operations[0]/data");
@@ -281,6 +281,45 @@ public async Task Cannot_create_resource_for_incompatible_ID()
         error.Meta.ShouldContainKey("requestBody").With(value => value.ShouldNotBeNull().ToString().ShouldNotBeEmpty());
     }
 
+    [Fact]
+    public async Task Cannot_create_resource_with_local_ID()
+    {
+        // Arrange
+        var requestBody = new
+        {
+            atomic__operations = new[]
+            {
+                new
+                {
+                    op = "add",
+                    data = new
+                    {
+                        type = "textLanguages",
+                        lid = "new-server-id"
+                    }
+                }
+            }
+        };
+
+        const string route = "/operations";
+
+        // Act
+        (HttpResponseMessage httpResponse, Document responseDocument) = await _testContext.ExecutePostAtomicAsync<Document>(route, requestBody);
+
+        // Assert
+        httpResponse.ShouldHaveStatusCode(HttpStatusCode.UnprocessableEntity);
+
+        responseDocument.Errors.ShouldHaveCount(1);
+
+        ErrorObject error = responseDocument.Errors[0];
+        error.StatusCode.Should().Be(HttpStatusCode.UnprocessableEntity);
+        error.Title.Should().Be("Failed to deserialize request body: The 'lid' element cannot be used because a client-generated ID is required.");
+        error.Detail.Should().BeNull();
+        error.Source.ShouldNotBeNull();
+        error.Source.Pointer.Should().Be("/atomic:operations[0]/data/lid");
+        error.Meta.ShouldContainKey("requestBody").With(value => value.ShouldNotBeNull().ToString().ShouldNotBeEmpty());
+    }
+
     [Fact]
     public async Task Cannot_create_resource_for_ID_and_local_ID()
     {