StringAggregate with GroupBy on SQL Server

[brianvonkuster]

Hi,

I've been running into an issue when trying to use StringAggregate with a GroupBy clause when executing against SQL Server (2017, 2019, 2022).

When I run the equivalent of the following code:

public class ProductInfo
{
	public int Id { get; set; }
	public string AggregatedDescription { get; set; }
}

public class Product {
	[Column]
	public int Id { get; set; }
	
	[Column]
	public string Description { get; set; }
}

public class ProductService {
	public ITable<Product> Products => GetTable<Product>();

	public IEnumerable<ProductInfo> GetAggregatedDescriptions() 
	{
		var productsGrouped = Products
			.GroupBy(x => x.Id)
			.Select(g => new ProductInfo {
				Id = g.Key,
				AggregatedDescription = g.StringAggregate(", ", x => x.Description)
			});
			
		return productsGrouped.ToList();
	}
}

I get an exception thrown --

LinqToDB.LinqToDBException: 'You should explicitly specify selected fields for server-side GroupBy() call or add AsEnumerable() call before GroupBy() to perform client-side grouping.
Set Configuration.Linq.GuardGrouping = false to disable this check.
Additionally this guard exception can be disabled by extension GroupBy(...).DisableGuard() or using options.UseGuardGrouping(false) configuration extension.

Disabling the guard doesn't seem to help, as Linq2Db throws an exception saying StringAggregate is a serverside function. Not sure if this is a potential bug or I'm doing something wrong, I've tried several permutations including g.StringAggregate(", ", x => x.Description).ToValue() to no avail.

[sdanyliv]

Looks like you have returned tuple (int Id, string AggregatedDescription), but query is written using anonymous class. Where is true?

g.StringAggregate(", ", x => x.Description).ToValue() - should be right.

[brianvonkuster]

Whoops, sorry. I was cutting a class out and messed that up. I edited the example to be fully functional now.

I tried g.StringAggregate(", ", x => x.Description).ToValue(), however when I do that I get the exception LinqToDB.Linq.LinqException: ''g.StringAggregate(", ", x => x.Description).ToValue()' cannot be converted to SQL.'