Interview Q&A

Short answer: EF Core uses migrations to track and apply schema changes: You modify your C# models. Use Add-Migration to create a migration class. Use Update-Database to apply the changes to the DB. EF Core compares the model to the current schema to generate SQL.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: 🧩 Data Annotations (in the entity class): [Table("Users")] public class User

Example code

{ [Key] public int Id { get; set; } [Column("UserName")] public string Name { get; set; }
} 🧠 Fluent API (in OnModelCreating): modelBuilder.Entity<User>() .ToTable("Users") .HasKey(u => u.Id); modelBuilder.Entity<User>() .Property(u => u.Name) .HasColumnName("UserName"); 📌 Fluent API is more powerful and flexible, preferred for complex configurations.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Migrations in EF Core are a way to: Track schema changes over time Apply those changes to the database 📦 Basic commands: Add-Migration MigrationName Update-Database Remove-Migration Script-Migration 🔄 Migrations are classes containing Up() and Down() methods (for applying and reverting changes). 📌 They are essential for schema versioning in Code First. Entity Framework Core – Migrations Interview Questions

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: How are they used in Code First? Migrations in EF Core are a way to: Track schema changes over time Apply those changes to the database 📦 Basic commands: Add-Migration MigrationName Update-Database Remove-Migration Script-Migration 🔄 Migrations are classes containing Up() and Down() methods (for applying and reverting changes). 📌 They are essential for schema versioning in Code First. Entity Framework Core –…

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dd-Migration MigrationName This creates a migration file with Up() and Down() methods, and a snapshot of the current model.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: (e.g. Add-Migration) Use one of the following commands: .NET CLI: dotnet ef migrations add MigrationName Package Manager Console: Add-Migration MigrationName This creates a migration file with Up() and Down() methods, and a snapshot of the current model.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pply the migration to your database using: .NET CLI: dotnet ef database update Package Manager Console: Update-Database EF Core translates your model changes into SQL and executes them against the database.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: (e.g. Update-Database) Apply the migration to your database using: .NET CLI: dotnet ef database update Package Manager Console: Update-Database EF Core translates your model changes into SQL and executes them against the database.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: A migration snapshot is a C# file (e.g., ModelSnapshot.cs) automatically created by EF Core. It represents the current model state. EF uses it to compare changes in future migrations. Located in the Migrations folder, named like [YourDbContext]ModelSnapshot.cs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: To remove the last migration before applying it: dotnet ef migrations remove To rollback the database to a previous migration: dotnet ef database update MigrationName To rollback all migrations: dotnet ef database update 0

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Generate SQL script using: dotnet ef migrations script To script a specific range: dotnet ef migrations script FromMigration ToMigration These scripts are useful for deploying to production environments or executing via CI/CD pipelines.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: How to generate SQL scripts for migrations? Generate SQL script using: dotnet ef migrations script To script a specific range: dotnet ef migrations script FromMigration ToMigration These scripts are useful for deploying to production environments or executing via CI/CD pipelines.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the HasData() method in OnModelCreating(): modelBuilder.Entity<User>().HasData( new User { Id = 1, Name = "Admin" } ); Data is inserted automatically during Update-Database. Changes to seed data require a new migration.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Best practices: Communicate and coordinate migration changes. Always pull and apply the latest migrations before adding a new one. If conflicts arise: Resolve merge conflicts in migration files manually. Rebuild ModelSnapshot as needed. Consider squashing or reorganizing migrations.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Generate SQL script from tested migrations. Manually review and apply via DBA or DevOps tools. Use EF Core tools in CI/CD (e.g., GitHub Actions, Azure DevOps): dotnet ef database update --no-build ● Always backup the database before applying migrations in production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Scaffolded migrations are the automatically generated classes that contain Up() and Down() methods. They are generated based on model differences. You can manually edit these files to: Add custom SQL Rename columns Seed data, etc.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: You can manually edit migration files after scaffolding: protected override void Up(MigrationBuilder migrationBuilder) { migrationBuilder.Sql("UPDATE Users SET IsActive = 1 WHERE IsActive IS NULL"); } Add indexes, constraints, stored procedures. Use raw SQL or Fluent API. Be cautious to maintain idempotency and correctness. Entity Framework Core – Change Tracking & Concurrency

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: fter they are loaded from the database. This allows EF Core to generate the correct SQL INSERT, UPDATE, or DELETE statements when SaveChanges() is called.

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Change tracking is the process by which EF Core keeps track of changes made to entities after they are loaded from the database. This allows EF Core to generate the correct SQL INSERT, UPDATE, or DELETE statements when SaveChanges() is called.

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dded New entity to be inserted into the database Modified Entity has been changed and will be updated Deleted Entity will be deleted from the database Detached Entity is not tracked by the context Unchange No changes have been made since it was loaded You can check/set the state via: context.Entry(entity).State = EntityState.Modified; Example… code dded… New… entity to be inserted into the database Modified Entity…

Explain a bit more

has been changed and will be updated Deleted Entity will be deleted from the database Detached Entity is not tracked by the context Unchange No changes have been made since it was loaded You can check/set the state via: context.Entry(entity).State = EntityState.Modified; dded New entity to be inserted into the database Modified Entity has been changed and will be updated Deleted Entity will be deleted from the database Detached Entity is not tracked by the context Unchange No changes have been made since it was loaded You can check/set the state via: context.Entry(entity).State = EntityState.Modified; Example… code dded New entity…

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: EF Core uses these EntityState values: State Description Added New entity to be inserted into the database Modified Entity has been changed and will be updated Deleted Entity will be deleted from the database Detached Entity is not tracked by the context Unchange No changes have been made since it was loaded You can check/set the state via: context.Entry(entity).State = EntityState.Modified;

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: re loaded, and compares them before saving. Notifications: If your entities implement INotifyPropertyChanged, EF can track changes immediately. EF compares the current values to the original snapshot during SaveChanges().

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: EF Core tracks changes via: Snapshot change tracking: EF stores a snapshot of original values when entities are loaded, and compares them before saving. Notifications: If your entities implement INotifyPropertyChanged, EF can track changes immediately. EF compares the current values to the original snapshot during SaveChanges().

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: re monitored and persisted. Untracked queries: EF does not monitor the returned entities. re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and…… persisted. Untracked queries: EF does not monitor the returned…

Explain a bit more

entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and persisted. Untracked queries: EF does not monitor the returned entities. re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default):…

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Tracked queries: EF Core tracks entities returned from the query. Changes to them are monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only access. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault();

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.