Entity Framework Core CosmosDB upsert (update/insert) recognition

I have a package I built a while back that works with EF-created SQL databases just great. I've recently had a call to try to use with CosmosDB and guid "primary keys". My first foray into Cosmos.

When saving records I'm checking the value of the primary key: if it's the default value for the type, I consider it an insert; if it's not, then I consider it an update.

public virtual TModel Save(TModel data)
    {
        _dynamic.Add(data);
        _context.Entry(data).State =
            data.Id.Equals(default(TKey))
                ? EntityState.Added 
                : EntityState.Modified;
        _context.SaveChanges();
        return data;
    }

I vaguely recall doing this for a performance reason, so I'm not pulling the records down from the database before updating them. It doesn't appear that there's a built-in upsert?

I believe the Id property is populated here on inserts for CosmosDB because CosmosDB doesn't generate its own Ids and instead relies on EF to provide it. Which is sensible, but breaks my convention here.

I suppose the ultimate question is, is there a better way to handle "upserts" here that doesn't rely on the Id being not-set?

More Info
The TModel data passed in is from a user request, at this point we:

1. Haven't pulled anything down from the database
2. Don't have any other records with pending changes in the context
3. There's another, nearly identical function that adds a range of data then calls SaveChanges so we are being somewhat diligent about work load here

The reason for doing the upsert pattern here is that the user has a single API endpoint that data gets saved to, whether it's a new record or an existing one.

We are essentially circumventing the DB upsert performance issues by telling it "this is an update" or "this is an insert" with this method, it's simply broken down because the Id for an inserted record is generated at this point for CosmosDB, where that wasn't an issue with the SQL version.

It looks as though I may just need to dig deeper into the CosmosDB internals and their EF interactions.

Entity Framework Core CosmosDB upsert (update/insert) recognition:

>Below is a better way to handle "upserts" here that doesn't rely on the Id being not-set

Explanation:

• A new data record of type TModel is created inside the try block, and an upsert operation is carried out using the repository.

• An upsert operation either creates a new document if it doesn't exist or updates an existing document.

• A query is defined in the upsert method to determine whether any existing data with the specified Role exists.

• A query iterator is used to perform the query, and the first result is obtained using.FirstOrDefault().

• If no existing data is found, a new "id" is generated for the document in case there is no existing data with the specified "Role" property else it updates the existing data.

var client = new CosmosClient(cosmosEndpoint, cosmosKey);
var cosmosContainer = client.GetContainer("upsertDb", "upsertCont");

var repository = new YourRepository(cosmosContainer);
try
 {
    var newData = new TModel
     {
       Role = "FullStackDeveloper",
       Name = "Balaji"
     };
Console.WriteLine($"Role: {newData.Role}");
await repository.Upsert(newData);

Console.WriteLine("Upsert operation completed successfully.");
 }
catch (CosmosException ex)
 {
   Console.WriteLine($"CosmosException: {ex.Message}");
   Console.WriteLine($"Status Code: {ex.StatusCode}");
 }
catch (Exception ex)
 {
   Console.WriteLine($"An unexpected error occurred: {ex.Message}");
 }

public class YourRepository
{
  private readonly Container _container;
  public YourRepository(Container container)
  {
     _container = container;
  }
  public async Task Upsert(TModel data)
   {
     var partitionKey = new PartitionKey(data.Role);
	 try
     {
       var query = new QueryDefinition($"SELECT * FROM c WHERE c.Role = @role").WithParameter("@role", data.Role);
       var queryIterator = _container.GetItemQueryIterator<TModel>(query);
       var existingData = (await queryIterator.ReadNextAsync()).FirstOrDefault();

       if (existingData == null)
       {
          data.id = Guid.NewGuid().ToString();
          await _container.CreateItemAsync(data, partitionKey);
       }
       else
       {
          data.id = existingData.id; // Set the existing 'id' before upserting
          await _container.UpsertItemAsync(data, partitionKey);
       }
     }
     catch (CosmosException ex)
     {
       throw;
     }
   }
}

Output: