Interview Q&A

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.

🧩 Data Annotations (in the entity class):

[Table("Users")]

public class User
{

[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.

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

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 – Migrations

Interview Questions

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

(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.

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• 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.

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

• 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.

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

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;

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;

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().

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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().

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();

• 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();