Tutorials Entity Framework Core Tutorial
LINQ Introduction for EF Core
LINQ Introduction for EF Core: free step-by-step lesson with examples, common mistakes, and interview tips — part of Entity Framework Core Tutorial on Toolliyo Academy.
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Entity Framework Core Tutorial · Lesson 31 of 100
LINQ Introduction for EF Core
Beginner ✓ → Intermediate → Advanced → Professional
Intermediate · 2 — Data & queries · ~6 min · Module 4: LINQ
What is this?
LINQ (Language Integrated Query) lets you query DbSet with C# operators. EF Core translates expression trees to SQL when you execute with ToListAsync, CountAsync, or similar.
Why should you care?
ShopNest search composes filters in C# — compile-time checking beats fragile string SQL when Product properties rename.
See it live — copy this example
Paste into a .NET project with EF Core packages, then run with LocalDB/SQL Server (dotnet ef / dotnet run).
IQueryable<Product> query = _context.Products;
if (minPrice.HasValue)
query = query.Where(p => p.Price >= minPrice.Value);
if (!string.IsNullOrEmpty(term))
query = query.Where(p => p.Name.Contains(term));
var results = await query.OrderBy(p => p.Name).ToListAsync();What happened?
- IQueryable stays deferred — each Where adds to expression tree.
- ToListAsync compiles one SQL SELECT with all filters and ORDER BY.
Practice next
- Build query stepwise and predict SQL before execution.
- Move filter values to variables and rebuild.
- Compare generated SQL with hand-written SELECT in SSMS.
- Inspect query.ToQueryString() before ToListAsync (EF Core 5+).
- Add impossible filter and verify empty list without SQL error.
Remember
IQueryable defers SQL until execution. Compose filters before materializing. EF translates expression trees to SQL.
ShopNest faceted search
Search API builds IQueryable with optional price and keyword filters shared by web and mobile.
Outcome: One query pipeline serves multiple clients with identical SQL.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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