Interview question and answer on Entity Framework with full explanation and code example

Here are 40 commonly asked interview questions and answers on Entity Framework, along with explanations and code examples:

Question 1: What is Entity Framework (EF)? 

Answer: 

Entity Framework is an Object-Relational Mapping (ORM) framework provided by Microsoft. It enables developers to work with databases using .NET objects, abstracting away the underlying database-specific details.

Question 2: What are the different versions of Entity Framework? 

Answer: The different versions of Entity Framework are EF1 (Entity Framework 1.0), EF4 (Entity Framework 4.0), EF5 (Entity Framework 5.0), EF6 (Entity Framework 6.0), and EF Core (Entity Framework Core).

Question 3: What is the difference between Entity Framework and Entity Framework Core? 

Answer: Entity Framework (EF) is the full version of the framework, while Entity Framework Core (EF Core) is a lightweight, cross-platform version built from scratch with a focus on performance and support for non-relational databases.

Question 4: What are the advantages of using Entity Framework? 

Answer: The advantages of using Entity Framework include automatic object-relational mapping, increased productivity, simplified data access code, improved maintainability, and support for various database providers.

Question 5: Explain the DbContext class in Entity Framework. 

Answer: The DbContext class is the primary class in Entity Framework for interacting with the database. It represents a session with the database and provides methods for querying, inserting, updating, and deleting entities.

csharp
public class MyDbContext : DbContext
{
    public DbSet<Customer> Customers { get; set; }
    public DbSet<Order> Orders { get; set; }
}

Question 6: How can you configure a connection string in Entity Framework? 

Answer: The connection string can be configured in the application's configuration file (e.g., web.config or app.config) using the <connectionStrings> section or provided directly in code when creating an instance of the DbContext.

Question 7: Explain Code First approach in Entity Framework. 

Answer: Code First is an approach in Entity Framework where you define your domain model classes and relationships first, and the database schema is generated automatically based on these classes.

Question 8: How do you define a primary key using Code First approach in Entity Framework? 

Answer: In Code First, you can define a primary key by using the [Key] attribute on the corresponding property or by using the HasKey() method in the DbContext's OnModelCreating() method.

csharp
public class Customer
{
    [Key]
    public int Id { get; set; }
    // other properties
}

Question 9: How do you define relationships between entities using Code First approach in Entity Framework? 

Answer: Relationships between entities can be defined by using navigation properties and configuration in the DbContext's OnModelCreating() method. For example, a one-to-many relationship can be defined using the [ForeignKey] attribute or the HasForeignKey() method.

csharp
public class Order
{
    public int Id { get; set; }
    public int CustomerId { get; set; }

    [ForeignKey("CustomerId")]
    public Customer Customer { get; set; }
}

Question 10: What is Database First approach in Entity Framework? 

Answer: Database First is an approach in Entity Framework where the database schema is already defined, and the corresponding entity classes and mappings are generated automatically from the database.

Question 11: What is Model First approach in Entity Framework? 

Answer: Model First is an approach in Entity Framework where you design the entity model using the Entity Framework Designer, and the database schema and corresponding classes are generated from the model.

Question 12: How do you perform eager loading in Entity Framework? 

Answer: Eager loading can be achieved by using the Include() method to include related entities while querying.

csharp
var customers = context.Customers.Include(c => c.Orders).ToList();

Question 13: What is lazy loading in Entity Framework? 

Answer: Lazy loading is a feature in Entity Framework where related entities are loaded from the database automatically when accessed for the first time. It helps avoid loading unnecessary data upfront.

Question 14: How do you disable lazy loading in Entity Framework? 

Answer: Lazy loading can be disabled by setting the LazyLoadingEnabled property to false in the DbContext's constructor or configuration.

csharp
public class MyDbContext : DbContext
{
    public MyDbContext()
    {
        this.Configuration.LazyLoadingEnabled = false;
    }
}

Question 15: What is explicit loading in Entity Framework? 

Answer: Explicit loading is a technique in Entity Framework to selectively load related entities using the Load() method or by accessing the navigation properties explicitly.

csharp
var customer = context.Customers.Find(1);
context.Entry(customer).Collection(c => c.Orders).Load();

Question 16: What is the difference between SaveChanges() and SaveChangesAsync() in Entity Framework? 

Answer: SaveChanges() is a synchronous method in Entity Framework that saves all changes to the database and returns the number of affected rows. SaveChangesAsync() is an asynchronous version of the method that returns a Task<int> and allows for better scalability and responsiveness in applications.

Question 17: How do you execute raw SQL queries in Entity Framework? 

Answer: Entity Framework allows executing raw SQL queries using the SqlQuery() method or the ExecuteSqlCommand() method.

csharp
var customers = context.Database.SqlQuery<Customer>("SELECT * FROM Customers").ToList();

var result = context.Database.ExecuteSqlCommand("UPDATE Customers SET Name = 'John' WHERE Id = 1");

Question 18: How can you handle database transactions in Entity Framework? 

Answer: Entity Framework supports database transactions through the Database.BeginTransaction() method. You can explicitly begin, commit, or rollback transactions as needed.

csharp
using (var dbContextTransaction = context.Database.BeginTransaction())
{
    try
    {
        // Perform database operations

        context.SaveChanges();
        dbContextTransaction.Commit();
    }
    catch
    {
        dbContextTransaction.Rollback();
    }
}

Question 19: What is a migration in Entity Framework? 

Answer: Migrations in Entity Framework are a way to manage changes to the database schema over time. They enable developers to update the database schema automatically based on changes in the model.

Question 20: How do you enable and run migrations in Entity Framework? 

Answer: Migrations can be enabled by running the Enable-Migrations command in the Package Manager Console. Subsequently, you can use the Add-Migration command to create a new migration and the Update-Database command to apply the pending migrations.

Question 21: How do you seed initial data using migrations in Entity Framework? 

Answer: You can override the Seed() method in the database initializer or create a custom migration and use the Sql() method to execute SQL statements for seeding data.

csharp
public class MyInitializer : CreateDatabaseIfNotExists<MyDbContext>
{
    protected override void Seed(MyDbContext context)
    {
        // Seed initial data
    }
}

Question 22: What is the difference between AsNoTracking() and AsTracking() in Entity Framework? 

Answer: AsNoTracking() is a method in Entity Framework that specifies that the queried entities should not be tracked by the context, resulting in improved performance but without change tracking capabilities. AsTracking() (default behavior) tracks the queried entities and enables change tracking for updates.

Question 23: How do you handle concurrency conflicts in Entity Framework? 

Answer: Entity Framework provides support for handling concurrency conflicts using the Timestamp or RowVersion attribute on properties. When a concurrency conflict occurs, an exception is thrown, and you can decide how to handle it.

csharp
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    
    [Timestamp]
    public byte[] RowVersion { get; set; }
}

Question 24: What is a database context factory in Entity Framework? 

Answer: A database context factory is a way to create instances of the DbContext class dynamically, allowing for more flexibility and control in managing the DbContext's lifetime.

Question 25: How do you handle stored procedures in Entity Framework? 

Answer: Entity Framework allows executing stored procedures using the SqlQuery() method or by mapping stored procedures to methods in the DbContext using the DbSet<T>.FromSql() method or the Database.ExecuteSqlCommand() method.

csharp
var customers = context.Database.SqlQuery<Customer>("EXEC GetCustomers").ToList();

var customers = context.Customers.FromSql("EXEC GetCustomers").ToList();

context.Database.ExecuteSqlCommand("EXEC UpdateCustomer @Id, @Name", 
    new SqlParameter("Id", 1),
    new SqlParameter("Name", "John"));

Question 26: How can you improve Entity Framework performance? 

Answer: To improve Entity Framework performance, you can use techniques such as minimizing the number of database round-trips, using appropriate query optimizations (e.g., indexing), caching, and optimizing the database schema.

Question 27: What is a database-first mapping strategy in Entity Framework? 

Answer: A database-first mapping strategy is an approach in Entity Framework where the entity classes and mappings are generated automatically from an existing database schema.

Question 28: What is a code-first mapping strategy in Entity Framework? 

Answer: A code-first mapping strategy is an approach in Entity Framework where you define the entity classes and relationships first, and the database schema is generated automatically based on these classes.

Question 29: How can you improve the performance of Entity Framework queries? 

Answer: To improve query performance in Entity Framework, you can use techniques like eager loading, lazy loading, explicit loading, projection queries, and optimizing LINQ queries by considering database indexes and reducing unnecessary data retrieval.

Question 30: How can you execute raw SQL queries safely to prevent SQL injection in Entity Framework? 

Answer: To prevent SQL injection, you should use parameterized queries when executing raw SQL queries in Entity Framework. Parameters should be passed as arguments to the query instead of concatenating them into the SQL string directly.

csharp
var id = 1;
var query = "SELECT * FROM Customers WHERE Id = @Id";
var customers = context.Database.SqlQuery<Customer>(query, new SqlParameter("Id", id)).ToList();

Question 31: What is an Entity Framework proxy? 

Answer: An Entity Framework proxy is a dynamically created subclass of an entity class that enables additional features such as lazy loading, change tracking, and proxy-based change detection.

Question 32: How do you disable Entity Framework proxy creation? 

Answer: Proxy creation can be disabled by setting the ProxyCreationEnabled property to false in the DbContext's constructor or configuration.

csharp
public class MyDbContext : DbContext
{
    public MyDbContext()
    {
        this.Configuration.ProxyCreationEnabled = false;
    }
}

Question 33: What is eager loading in Entity Framework? 

Answer: Eager loading is a technique in Entity Framework where related entities are loaded from the database along with the main entity in a single query, reducing the number of database round-trips.

Question 34: How do you define a many-to-many relationship using Code First approach in Entity Framework? 

Answer: To define a many-to-many relationship using Code First, you need to introduce a junction table and configure the relationships using the HasMany() and WithMany() methods.

csharp
public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    
    public ICollection<Course> Courses { get; set; }
}

public class Course
{
    public int Id { get; set; }
    public string Name { get; set; }
    
    public ICollection<Student> Students { get; set; }
}

// Configuration in DbContext's OnModelCreating method
modelBuilder.Entity<Student>()
    .HasMany(s => s.Courses)
    .WithMany(c => c.Students)
    .Map(cs =>
    {
        cs.MapLeftKey("StudentId");
        cs.MapRightKey("CourseId");
        cs.ToTable("StudentCourses");
    });

Question 35: How do you enable lazy loading in Entity Framework? 

Answer: Lazy loading is enabled by default in Entity Framework. However, if it's disabled, you can enable it by setting the LazyLoadingEnabled property to true in the DbContext's constructor or configuration.

csharp
public class MyDbContext : DbContext
{
    public MyDbContext()
    {
        this.Configuration.LazyLoadingEnabled = true;
    }
}

Question 36: How do you specify table and column names in Entity Framework using attributes? 

Answer: Table and column names can be specified in Entity Framework using attributes such as [Table] and [Column].

csharp
[Table("Customers")]
public class Customer
{
    [Column("CustomerID")]
    public int Id { get; set; }
    
    [Column("FullName")]
    public string Name { get; set; }
}

Question 37: How do you configure Entity Framework to use a different database provider? 

Answer: Entity Framework allows you to use different database providers by configuring the provider-specific settings in the application's configuration file and specifying the provider in the connection string.

Question 38: What is a navigation property in Entity Framework? 

Answer: A navigation property in Entity Framework represents the relationship between entities. It allows you to navigate and access related entities.

Question 39: How do you execute a stored procedure that returns multiple result sets in Entity Framework? 

Answer: To execute a stored procedure that returns multiple result sets, you can use the Translate<T>() method or the NextResult() method.

csharp
var results = context.Database.SqlQuery<Customer>("EXEC GetCustomersMultipleResultSets").ToList();

using (var reader = context.Database.SqlQuery<Customer>("EXEC GetCustomersMultipleResultSets").GetEnumerator())
{
    var customers = ((IObjectContextAdapter)context).ObjectContext.Translate<Customer>(reader);
    reader.NextResult();
    var orders = ((IObjectContextAdapter)context).ObjectContext.Translate<Order>(reader);
}

Question 40: How do you configure Entity Framework to use an existing database schema? 

Answer: To use an existing database schema in Entity Framework, you can use the Database First approach or the Code First approach with Data Annotations or Fluent API to configure the entity classes and mappings to match the existing schema.

These interview questions and answers provide a comprehensive overview of Entity Framework and cover various aspects of its usage. Remember to adapt your answers based on your specific experience and knowledge of Entity Framework.