[Cosmos] ISO date time strings are not read back correctly from the database

[anttikes]

Include your code

A sample application which reproduces the various the scenarios is attached to this post. The project attempts to connect to a CosmosDB emulator running on the local computer. The problem scenario has not been tested against an Azure CosmosDB account.

EFCoreISODatesBug.zip

Include provider and version information

EF Core version: 5.0.9
Database provider: Microsoft.EntityFrameworkCore.Cosmos
Database provider version: 5.0.9
Underlying Azure SDK version: 3.12.0
Target framework: .NET 5.0
Operating system: Windows 10 Enterprise (version "10.0.19043 Build 19043")
IDE: Visual Studio 2019 version 16.11.1
CosmosDB Emulator version: 2.14.1.0 (08dca53e)
Operating system time zone settings: "UTC+02:00 Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius"

Reproduction steps

1. Open up the sample application in Visual Studio
2. Build it
3. Run it

Expected result

Since the model uses a plain string as the property's type the expected behavior is that the strings are saved into CosmosDB as-is, and when they are read back they are still exactly the same as before.

Observed behavior

The items are written correctly to the CosmosDB container, and the content of the documents therein corresponds exactly to the expected outcome.

When the items are read back from CosmosDB then the ISODate property is formatted differently, and the time stamp has automatically been adjusted by the UTC offset. On my computer, the adjustment that is done to the time stamp looks incorrect as well:

Re-creating database

Writing new item to database '4617064c-382a-409c-8caa-d6e8f88471f2'
        - ISODate: '2021-08-23T06:23:40Z'

Writing new item to database '39d830c6-c486-49b9-8464-4892d81b89d5'
        - ISODate: '2021-08-23T06:23:40+00:00'

Writing new item to database '28f12faa-dedd-4b0d-ae28-f739f4ce2102'
        - ISODate: '2021-08-23T06:23:40+02:00'

Reading back item '4617064c-382a-409c-8caa-d6e8f88471f2'
        - ISODate: '08/23/2021 06:23:40'

Reading back item '39d830c6-c486-49b9-8464-4892d81b89d5'
        - ISODate: '08/23/2021 09:23:40'

Reading back item '28f12faa-dedd-4b0d-ae28-f739f4ce2102'
        - ISODate: '08/23/2021 07:23:40'

Output from 'dotnet --info'

.NET SDK (reflecting any global.json):
 Version:   5.0.400
 Commit:    d61950f9bf

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19043
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\5.0.400\

Host (useful for support):
  Version: 5.0.9
  Commit:  208e377a53

.NET SDKs installed:
  3.1.412 [C:\Program Files\dotnet\sdk]
  5.0.104 [C:\Program Files\dotnet\sdk]
  5.0.203 [C:\Program Files\dotnet\sdk]
  5.0.206 [C:\Program Files\dotnet\sdk]
  5.0.303 [C:\Program Files\dotnet\sdk]
  5.0.400 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[ajcvickers]

@anttikes This appears to be an issue with the underlying Cosmos API or the Cosmos database implementation itself. EF Core simply treats these values as strings; it never attempts to parse them as dates. I would suggest you fil an issue with Cosmos, possibly starting here: https://github.com/Azure/azure-cosmos-dotnet-v3

[anttikes]

@ajcvickers Thank you for your investigation. I haver reported the issue to the Cosmos SDK repository that you linked. Hopefully they can figure it out.

I'll close this issue. If the Cosmos SDK team reports that the bug is in EF Core then I'll re-open it with whatever relevant details they can provide.

[AndriySvyryd]

@anttikes You can work around this by calling
Storage.Internal.CosmosClientWrapper.Serializer.DateParseHandling = Newtonsoft.Json.DateParseHandling.None;

[anttikes]

Thanks @AndriySvyryd for the tip. I think our team can afford to wait for the next release where your fix is included.