Optimizing EF Core Queries

When to Use

• EF Core queries are slow or generating too many SQL statements

• Database CPU/IO is high due to ORM inefficiency

• N+1 query patterns are detected in logs

• Large result sets cause memory pressure

When Not to Use

• The user is using Dapper or raw ADO.NET (not EF Core)

• The performance issue is database-side (missing indexes, bad schema)

• The user is building a new data access layer from scratch

Inputs

Input

Required

Description

Slow EF Core queries

Yes

The LINQ queries or DbContext usage to optimize

SQL output or logs

No

EF Core generated SQL or query execution logs

Workflow

Step 1: Enable query logging to see the actual SQL

// In Program.cs or DbContext configuration:

optionsBuilder

    .UseSqlServer(connectionString)

    .LogTo(Console.WriteLine, LogLevel.Information)

    .EnableSensitiveDataLogging()  // shows parameter values (dev only!)

    .EnableDetailedErrors();

Or use the Microsoft.EntityFrameworkCore log category:

{

  "Logging": {

    "LogLevel": {

      "Microsoft.EntityFrameworkCore.Database.Command": "Information"

    }

  }

}

Step 2: Fix N+1 query patterns

The #1 EF Core performance killer. Happens when loading related entities in a loop.

Before (N+1 — 1 query for orders + N queries for items):

var orders = await db.Orders.ToListAsync();

foreach (var order in orders)

{

    // Each access triggers a lazy-load query!

    var items = order.Items.Count;

}

After (eager loading — 1 or 2 queries total):

// Option 1: Include (JOIN)

var orders = await db.Orders

    .Include(o => o.Items)

    .ToListAsync();

// Option 2: Split query (separate SQL, avoids cartesian explosion)

var orders = await db.Orders

    .Include(o => o.Items)

    .AsSplitQuery()

    .ToListAsync();

// Option 3: Explicit projection (best - only fetches needed columns)

var orderSummaries = await db.Orders

    .Select(o => new OrderSummary

    {

        OrderId = o.Id,

        Total = o.Items.Sum(i => i.Price),

        ItemCount = o.Items.Count

    })

    .ToListAsync();

When to use Split vs Single query:

Scenario

Use

1 level of Include

Single query (default)

Multiple Includes (Cartesian risk)

AsSplitQuery()

Include with large child collections

AsSplitQuery()

Need transaction consistency

Single query

Step 3: Use NoTracking for read-only queries

Change tracking overhead is significant. Disable it when you don't need to update entities:

// Per-query

var products = await db.Products

    .AsNoTracking()

    .Where(p => p.IsActive)

    .ToListAsync();

// Global default for read-heavy apps

services.AddDbContext<AppDbContext>(options =>

    options.UseSqlServer(connectionString)

           .UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking));

**Use AsNoTrackingWithIdentityResolution() when the query returns duplicate entities to avoid duplicated objects in memory.**

Step 4: Use compiled queries for hot paths

// Define once as static

private static readonly Func<AppDbContext, int, Task<Order?>> GetOrderById =

    EF.CompileAsyncQuery((AppDbContext db, int id) =>

        db.Orders

            .Include(o => o.Items)

            .FirstOrDefault(o => o.Id == id));

// Use repeatedly — skips query compilation overhead

var order = await GetOrderById(db, orderId);

Step 5: Avoid common query traps

Trap

Problem

Fix

ToList() before Where()

Loads entire table into memory

Filter first: .Where().ToList()

Count() to check existence

Scans all rows

Use .Any() instead

.Select() after .Include()

Include is ignored with projection

Remove Include, use Select only

string.Contains() in Where

May not translate, falls to client eval

Use EF.Functions.Like() for SQL LIKE

Calling .ToList() inside Select()

Causes nested queries

Use projection with Select all the way

Step 6: Use raw SQL or FromSql for complex queries

When LINQ can't express it efficiently:

var results = await db.Orders

    .FromSqlInterpolated($@"

        SELECT o.* FROM Orders o

        INNER JOIN (

            SELECT OrderId, SUM(Price) as Total

            FROM OrderItems

            GROUP BY OrderId

            HAVING SUM(Price) > {minTotal}

        ) t ON o.Id = t.OrderId")

    .AsNoTracking()

    .ToListAsync();

Validation

• SQL logging shows expected number of queries (no N+1)

• Read-only queries use AsNoTracking()

• Hot-path queries use compiled queries

• No client-side evaluation warnings in logs

• Include/split strategy matches data shape

Common Pitfalls

Pitfall

Solution

Lazy loading silently creating N+1

Remove Microsoft.EntityFrameworkCore.Proxies or disable lazy loading

Global query filters forgotten in perf analysis

Check HasQueryFilter in model config; use IgnoreQueryFilters() if needed

DbContext kept alive too long

DbContext should be scoped (per-request); don't cache it

Batch updates fetching then saving

EF Core 7+: use ExecuteUpdateAsync / ExecuteDeleteAsync for bulk operations

String interpolation in FromSqlRaw

SQL injection risk — use FromSqlInterpolated (parameterized)