Cosmos DateTime Serialization

[cliedeman]

File a bug

Cosmos Provider DateTime Serialization does not serialize in the expected format: yyyy-MM-ddTHH:mm:ss.fffffffZ

Include your code

Create any model that contains a DateTime and save it to cosmos

class Document {
  public Guid Id { get; set; }

  public DateTime Timestamp {get;set;}
}

{
    "id": "cd081158-d474-43aa-b115-150f1d162e1d",
    "_ts": 1732385644,
    "$type": "Document",
    "_etag": "d401e28f-58dd-43df-895f-cf02b9cc2e18",
    "_self": "dbs/cosmosdb/colls/Document/docs/cd081158-d474-43aa-b115-150f1d162e1d/",
    "Timestamp": "2021-01-01T02:00:00+02:00",
}

The serialized timestamp does not follow the cosmos recommendations:

https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/query/working-with-dates#storing-datetimes.

Related to Azure/azure-cosmos-dotnet-v3#4904 but I dont believe the ef core cosmos provider uses Json Serialization

Include provider and version information

EF Core version:
Database provider: (e.g. Microsoft.EntityFrameworkCore.SqlServer)
Target framework: (e.g. .NET 6.0)
Operating system:
IDE: (e.g. Visual Studio 2022 17.4)

[roji]

In what way is the serialization not in the expected format? Are you referring to the lack of the .fffffff component? If so, then AFAIK ISO9601 allows omitting it when it's zero; try setting your DateTime to a timestamp which contains a sub-millisecond component, and you should see it serialized.

Otherwise, if I haven't understood what you're saying, please provide more details/context.

[cliedeman]

Hi @roji I figured out my issue.

The DateTime kind was local and not UTC. After changing it to UTC it was saved in the expected format.

The other issue is that the date in question is not valid according to the dotnet date format

DateTimeOffset.ParseExact(
            "2021-01-01T02:00:00+02:00",
            "yyyy-MM-ddTHH:mm:ssZ",
            CultureInfo.InvariantCulture);

fails with

String '2021-01-01T02:00:00+02:00' was not recognized as a valid DateTime.

where as

DateTimeOffset.ParseExact(
            "2021-01-01T02:00:00Z",
            "yyyy-MM-ddTHH:mm:ssZ",
            CultureInfo.InvariantCulture);

passes.

Atleast to my understanding if the Z is present in the format only Z will be accepted and not an offset