Interview Q&A

Feature EF6 EF Core

Platform .NET Framework only Cross-platform (.NET Core)

Performance Slower Faster and more optimized

LINQ support Limited Enhanced

Change

tracking

Basic More efficient

Migrations Available Improved and CLI-friendly

Extensibility Limited Highly extensible

column. EF Core uses conventions or Fluent API to configure the mappings.

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: Entities are .NET classes that represent database tables. Each property in the entity maps to a column. EF Core uses conventions or Fluent API to configure the mappings.

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: Scalar: Simple types like int, string, DateTime Complex: Nested objects mapped to multiple columns (Value objects) Shadow: Properties not defined in the .NET class but tracked by EF Core

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: Productivity via abstraction from SQL Cross-platform support Strongly-typed LINQ queries Migration support Tracks changes automatically Works well with dependency injection

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.

• May generate inefficient SQL for complex queries
• Learning curve for advanced features
• Less control over fine-tuned SQL performance
• Not ideal for high-performance bulk operations

Entity Framework Core – Schema Design &

Migrations Interview Questions

Use the CLI or Package Manager Console:

dotnet ef dbcontext scaffold "YourConnectionString"

Microsoft.EntityFrameworkCore.SqlServer -o Models

OR

Scaffold-DbContext "YourConnectionString"

Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

✅ It generates:

• Entity classes
• DbContext class
• Mappings based on database schema

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.

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

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;