[BUG] Spring @DateTimeFormat(iso = ISO.DATE_TIME) not working with Cosmos DB

[GustavoOS]

Describe the bug
Despite expecting ISO-8601 string to be stored, the datetime is being stored as number, Applies for types LocalDateTime, Instant and ZonedDateTime and Date

Exception or Stack Trace
No exception thrown

To Reproduce

1. Create Model with ZonedDateTime property, using @DateTimeFormat(iso = ISO.DATE_TIME) annotation
2. Create Repository
3. Set spring boilerplate to create model instance and trigger save method of repository
4. Check Cosmos Explorer Items
   Model
   Code Snippet

import com.azure.spring.data.cosmos.core.mapping.Container;
import com.azure.spring.data.cosmos.core.mapping.PartitionKey;
import java.time.ZonedDateTime;
import java.util.UUID;
import lombok.Data;
import org.springframework.data.annotation.Id;
import org.springframework.format.annotation.DateTimeFormat;
import org.springframework.format.annotation.DateTimeFormat.ISO;

@Data
@Container(containerName = "FileMetaData")
public class MetaData {

  @Id
  UUID id;

  String safeName;
  String displayName;
  String mimeType;
  FileExtension extension;

  @DateTimeFormat(iso = ISO.DATE)
  ZonedDateTime createdAt = ZonedDateTime.now();

  @PartitionKey
  @DateTimeFormat(iso = ISO.DATE_TIME)
  ZonedDateTime deletedAt;
}

Repository

import com.azure.spring.data.cosmos.repository.CosmosRepository;
import com.azure.spring.data.cosmos.repository.Query;
import java.util.List;
import java.util.UUID;
import org.springframework.stereotype.Repository;


@Repository
public interface MetaDataRepository extends CosmosRepository<MetaData, UUID> { }

Expected behavior
Expected date to be stored as an ISO-8601 string

Screenshots

Setup (please complete the following information):

• OS: Windows 10
• IDE: IntelliJ
• Library/Libraries: spring-cloud-azure-starter-data-cosmos:4.7.0 (com.azure.spring)
• Java version: 17
• App Server/Environment: Tomcat
• Frameworks: Spring Boot 2.7.10, Cosmos Emulator 2.14.12.0

If you suspect a dependency version mismatch (e.g. you see NoClassDefFoundError, NoSuchMethodError or similar), please check out Troubleshoot dependency version conflict article first. If it doesn't provide solution for the problem, please provide:

• verbose dependency tree (mvn dependency:tree -Dverbose)
• exception message, full stack trace, and any available logs
  NA

Additional context
NA

Information Checklist
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• Repro Steps Added
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[kushagraThapar]

@trande4884 pls take a look, thanks!

[TheovanKraay]

Cosmos DB does not have any built-in date/time data types in the database. So whether stored as number or string, you have to do a conversion of the stored value back into a date/time if you want to work with it as a date/time again in your application... and that conversion is less costly when from numeric rather than string. Hence, I believe the decision was made in Spring Data Cosmos implementation to store these types as their numeric representations (number of seconds/milliseconds from epoch, using the given time zone, or local system clock in the case of LocalDateTime). Still, this could be reviewed, and either way made clearer in documentation.

[kushagraThapar]

@TheovanKraay please take a look at this, thanks!