Entity Framework Core

Learning objectives#

• Register EF Core with a context factory
• Query and save with short-lived contexts
• Use AsNoTracking for read-only lists
• Apply migrations

Explanation#

Register with AddDbContextFactory<ShopDb>. Inject IDbContextFactory<ShopDb> and create a context per operation with await using.

Read-only lists should use AsNoTracking() — faster, and no stale tracked entities.

Never run two queries on the same DbContext at the same time. With a factory, each operation has its own.

Migrations create and evolve the schema: dotnet ef migrations add, dotnet ef database update.

Code example: DbContext, factory and migrations#

1public class ShopDb(DbContextOptions<ShopDb> options) : DbContext(options)
2{
3    public DbSet<Product> Products => Set<Product>();
4    public DbSet<Category> Categories => Set<Category>();
5}
6

7// Program.cs
8builder.Services.AddDbContextFactory<ShopDb>(o =>
9    o.UseSqlServer(builder.Configuration.GetConnectionString("Shop")));
10

11// Usage in a service
12await using var db = await factory.CreateDbContextAsync();
13var cheap = await db.Products.AsNoTracking()
14    .Where(p => p.Price < 5000).OrderBy(p => p.Price).ToListAsync();
15

16// Terminal
17// dotnet ef migrations add InitialCreate
18// dotnet ef database update

The database is created from the model, and the query returns products under ₹5,000 using a fresh, untracked context.

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. The DbContext exposes Products and Categories.
2. AddDbContextFactory makes contexts on demand.
3. AsNoTracking skips change tracking for read-only data.
4. Migrations turn the model into tables.

Real-world use case#

Common mistakes#

Best practices#

• IDbContextFactory in Blazor
• AsNoTracking for reads
• Project to DTOs with Select
• Keep migrations in source control

Remember this#

Practice exercise#

1await using var db = await factory.CreateDbContextAsync();
2var p = await db.Products.FindAsync(id);
3if (p is not null) { p.Price = newPrice; await db.SaveChangesAsync(); }

Mini quiz#

Want more? Practise all Blazor MCQs · Blazor interview questions

Related topics#

My notes#

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