Provide more details by Miles

Grouping in EF Core

To group in EF Core using LINQ query syntax, use the group by clause followed by the grouping key and aggregate functions as needed. For example, to group a collection of items by a property called "Category" and count the items in each group:

var groupedData = from item in dbContext.Items
                  group item by item.Category into grouped
                  select new { Category = grouped.Key, Count = grouped.Count() };

Grouping by multiple columns in EF Core

The provided code snippet demonstrates a LINQ query to group by multiple columns while also finding the maximum item ID within each group. Here's a breakdown of the code:

var result = from o in context.Orders
             group o by new { o.CustomerId, o.OrderType } into g
             select new
             {
                 CustomerId = g.Key.CustomerId,
                 OrderType = g.Key.OrderType,
                 MaxItemId = g.Max(x => x.ItemId)
             };

In this code:

The group by new { o.CustomerId, o.OrderType } syntax allows grouping by a combination of CustomerId and OrderType using an anonymous type
The into g clause signifies that the grouped data will be accessible through the identifier g
The g.Key property allows access to the grouped key values, such as CustomerId and OrderType.
select new { ... } creates a new anonymous object for each group containing CustomerId, OrderType, and the maximum ItemId
The Max() method is used to find the maximum ItemId within each group (g.Max(x => x.ItemId))