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Grouping Smarter: LINQ GroupBy Enhancements in EF Core

Chris Woodruff
Grouping Smarter: LINQ GroupBy Enhancements in EF Core

Grouping data in Entity Framework Core (EF Core) used to feel a little… clunky. Sometimes, LINQ’s GroupBy() worked beautifully in-memory but got lost in translation when executing SQL queries. You’d write a simple GroupBy(), and EF Core would pull all the data into memory before doing the grouping—not good!

But things are getting smarter and more efficient in recent versions of EF Core! With LINQ GroupBy enhancements, EF Core now translates more grouping operations into optimized SQL queries, saving memory and improving performance.

Let’s explore what’s changed, how GroupBy() works in EF Core now, and how you can write better, faster queries for real-world scenarios!

What’s the Problem with LINQ GroupBy in EF Core?

Before the enhancements, using GroupBy() in EF Core often led to unexpected behavior. Unlike SQL’s GROUP BY, EF Core’s LINQ implementation sometimes performed the grouping in-memory, leading to:

Performance Issues – If you’re grouping thousands of rows, pulling them all into memory is a nightmare.
Inefficient Queries – Instead of optimizing grouping at the database level, EF Core used to fetch all the records first.
Hard-to-Debug Behavior – Depending on how you structured your query, you might get unexpected SQL translation issues.

Thankfully, EF Core now translates more GroupBy() queries into SQL instead of processing them in memory.

How LINQ GroupBy Works in EF Core Now

Let’s say we have a simple Sales database, where each order is tracked with:

public class Order
{
    public int Id { get; set; }
    public string Product { get; set; }
    public decimal Price { get; set; }
    public DateTime OrderDate { get; set; }
}

1. Old Problem: GroupBy in Memory (Bad Performance)

Before the enhancements, this query would not translate into SQL properly:

var salesReport = context.Orders
    .GroupBy(o => o.Product) // Will bring back all rows to be grouped in memory
    .Select(g => new { Product = g.Key, TotalSales = g.Sum(o => o.Price) })
    .ToList();

What EF Core Used to Do:

2. New Behavior: GroupBy Translates to SQL (Better Performance)

Now, in EF Core 6+, this query is properly translated into SQL:

var salesReport = await context.Orders
    .GroupBy(o => o.Product)
    .Select(g => new { Product = g.Key, TotalSales = g.Sum(o => o.Price) })
    .ToListAsync();

SQL Translation (EF Core 6+):

SELECT Product, SUM(Price) AS TotalSales
FROM Orders
GROUP BY Product;

Why is this awesome?

Real-World Examples Using GroupBy Enhancements

3. Grouping Orders by Month

Let’s say we want to generate monthly sales reports. Instead of fetching every order and grouping it in-memory, we can do this:

var monthlySales = await context.Orders
    .GroupBy(o => new { o.OrderDate.Year, o.OrderDate.Month })
    .Select(g => new
    {
        Year = g.Key.Year,
        Month = g.Key.Month,
        TotalRevenue = g.Sum(o => o.Price)
    })
    .ToListAsync();

SQL Translation:

SELECT YEAR(OrderDate) AS Year, MONTH(OrderDate) AS Month, SUM(Price) AS TotalRevenue
FROM Orders
GROUP BY YEAR(OrderDate), MONTH(OrderDate);

Now, grouping happens directly in SQL, making this much faster!

4. Counting Orders per Product

Need to know how many orders were placed for each product?

var productCounts = await context.Orders
    .GroupBy(o => o.Product)
    .Select(g => new { Product = g.Key, OrderCount = g.Count() })
    .ToListAsync();

SQL Translation:

SELECT Product, COUNT(*) AS OrderCount
FROM Orders
GROUP BY Product;

No more unnecessary in-memory calculations—everything is done efficiently at the database level!

5. Finding the Most Expensive Order per Product

Want to find the highest-priced order for each product? Easy!

var mostExpensiveOrders = await context.Orders
    .GroupBy(o => o.Product)
    .Select(g => new { Product = g.Key, MaxPrice = g.Max(o => o.Price) })
    .ToListAsync();

SQL Translation:

SELECT Product, MAX(Price) AS MaxPrice
FROM Orders
GROUP BY Product;

Fast, efficient, and no unnecessary in-memory processing.

When Does EF Core Still Struggle with GroupBy?

While EF Core now translates more GroupBy() queries into SQL, there are still some scenarios where in-memory execution might happen:

Grouping with Complex Object Projections – If you’re selecting entire entity objects, EF Core might switch to in-memory processing.
Grouping with Navigation Properties – If you’re trying to group by a related entity (o.Customer.Name instead of o.CustomerId), EF Core may struggle.
Mixing Client and Server Operations – If a part of your LINQ query cannot be translated into SQL, EF Core might switch the whole query to in-memory execution.

Final Thoughts: Grouping in EF Core is Now Smarter!

Grouping data used to be a headache in EF Core, but thanks to new enhancements, more GroupBy() queries now run at the database level instead of clogging up memory.

With these improvements, you can now:

So next time you need to group data in EF Core, trust the database to do the heavy lifting!

Have you tried the new GroupBy enhancements in EF Core? Let’s chat in the comments!

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