LastModified metadata not mapped into JSONB column on document creation

[jacek13]

Hi,
I recently had to configure metadata for new documents in one of our production applications that has been under development for quite some time.

I used Marten’s Metadata.MapTo configuration like this:

StoreOptions(c =>
{
    c.Schema.For<DocWithMeta>()
        .Metadata(m => m.LastModified.MapTo(x => x.LastModified));
});

However, while implementing create and update operations, I noticed an inconsistency in Marten’s behavior.

The table below shows how the values are assigned in each column:

	mt_last_modified	data->>'LastModified' (JSONB)
Create	Assigned value	Unassigned value
Update	Assigned value	Assigned value

Is it expected that the JSONB data column is not automatically filled when creating the document?

Below is a test that reproduces the issue.

namespace DocumentDbTests.Metadata
{
    public class document_metadata_specs : OneOffConfigurationsContext
    {
        [Fact]
        public async Task doc_has_projected_data_after_storage()
        {
            StoreOptions(c =>
            {
                c.Schema.For<DocWithMeta>()
                    .Metadata(m => m.LastModified.MapTo(x => x.LastModified));
            });

            var doc = new DocWithMeta();

            using (var session = theStore.LightweightSession())
            {
                session.Store(doc);
                (await session.MetadataForAsync(doc)).ShouldBeNull();
                await session.SaveChangesAsync();
            }

            using (var session = theStore.LightweightSession())
            {
                var loaded = await session.LoadAsync<DocWithMeta>(doc.Id);
                loaded.LastModified.ShouldNotBe(DateTimeOffset.MinValue);

                // I added the code below to reproduce the issue
                // mt_last_modified works fine. The value is assigned when the document is created
                var lastModifiedFromMetadataColumn = (await session
                    .QueryAsync<DateTimeOffset>("select mt_last_modified from document_metadata_specs.mt_doc_docwithmeta where id = ?", doc.Id))
                    .FirstOrDefault();
                lastModifiedFromMetadataColumn.ShouldNotBe(DateTimeOffset.MinValue);

                // LastModified property is not updated by Marten during document creation
                var lastModifiedFromDataColumn = (await session
                    .QueryAsync<DateTimeOffset>("select (data->>'LastModified')::timestamptz from document_metadata_specs.mt_doc_docwithmeta where id = ?", doc.Id))
                    .FirstOrDefault();
                lastModifiedFromDataColumn.ShouldNotBe(DateTimeOffset.MinValue);
                // This will trigger TESTERROR
                // Shouldly.ShouldAssertException : lastModifiedFromDataColumn
                // should not be
                // 1.01.0001 00:00:00 +00:00
                // but was
            }
        }

// rest of document_metadata_specs