LINQ Projection Performance Issues When Using Complex Select Statements in EF Core 6
I'm testing a new approach and I'm relatively new to this, so bear with me. I'm facing significant performance issues with a LINQ query that involves projecting into a complex anonymous type. The query works correctly but takes an unreasonable amount of time to execute, especially when the dataset grows. Here's the LINQ expression I'm currently using: ```csharp var result = await dbContext.Orders .Where(o => o.OrderDate >= startDate && o.OrderDate <= endDate) .Select(o => new { o.OrderId, o.Customer.Name, TotalAmount = o.OrderItems.Sum(oi => oi.Quantity * oi.Price), ItemCount = o.OrderItems.Count(), OrderStatus = o.Status }) .ToListAsync(); ``` I've indexed the `OrderDate`, but I suspect the complexity of the projection is slowing things down. Additionally, I noticed that the SQL generated by Entity Framework seems to be quite complex. The generated SQL looks like this: ```sql SELECT [o].[OrderId], [c].[Name] AS [CustomerName], (SELECT SUM([oi].[Quantity] * [oi].[Price]) FROM [OrderItems] AS [oi] WHERE [oi].[OrderId] = [o].[OrderId]) AS [TotalAmount], (SELECT COUNT(*) FROM [OrderItems] AS [oi] WHERE [oi].[OrderId] = [o].[OrderId]) AS [ItemCount], [o].[Status] FROM [Orders] AS [o] JOIN [Customers] AS [c] ON [o].[CustomerId] = [c].[CustomerId] WHERE [o].[OrderDate] >= @startDate AND [o].[OrderDate] <= @endDate ``` The performance improves significantly if I project only the `OrderId` and `OrderDate` instead of the entire object with computed properties. I've attempted to simplify the query by breaking it into two parts: fetching the relevant orders first and then performing the calculations in memory, but this approach leads to potential memory issues and still isn't optimal. Is there a way to enhance the performance of this query while keeping the necessary projections? Are there best practices for projecting complex types in EF Core that I might be overlooking? Any advice on indexing or restructuring the query to avoid performance degradation would be greatly appreciated. This is part of a larger CLI tool I'm building. I'd really appreciate any guidance on this. I'm using Csharp 3.11 in this project. Thanks, I really appreciate it! For context: I'm using Csharp on macOS. Is there a simpler solution I'm overlooking? What's the best practice here?