NULL JSON column prevents entity deserialization

[tunger]

Use case: migrate existing table/entity to Nevermore.

When adding a JSON column as NULLable, and it contains NULL, no properties are deserialized, not even column-bound properties.

    public class ReportState
    {
        public Guid CorrelationId { get; set; }
        public DateTime LastUpdatedTimestamp { get; set; }
    }

    public class ReportStateMap : DocumentMap<ReportState>
    {
        public ReportStateMap()
        {
            TableName = "ReportState";
            Id(x => x.CorrelationId);
            Column(x => x.LastUpdatedTimestamp);
        }
    }

Query

            var reportStates = reportTransaction.Query<ReportState>()
                .Where("CorrelationId IN @reportGuids")
                .OrderBy(x => x.CorrelationId)
                .Parameter("reportGuids", reportGuids)
                .ToList()
                .ToDictionary(x => x.CorrelationId);

Expected
Query should return list of ReportState correctly populated with data.

Actual
Empty list is returned.

Workaround
Update JSON column with '{}'

It should either throw if JSON is nullable, or handle NULL values as empty objects.

[PaulStovell]

I agree with your 'Expected' assertion. However, what if the type has no default constructor?

How's this for a proposal:

• If the type has a parameterless constructor, and the JSON is empty/null, new() it up
• If the type doesn't have a parameterless constructor, and the JSON is null/empty, throw

Let me know what you think.

I think it will just require a change to DocumentReaderContext.cs so that when told to deserialize, instead of returning null/ignoring, it calls the constructor or throws. Alternatively, we might need to change the generated code so that it does the null check and calls the constructor that way.