1. What is Entity Framework?
Entity Framework (EF) is an open-source Object-Relational Mapper (ORM) for .NET, developed by Microsoft. It enables developers to work with relational data as domain-specific objects, abstracting the underlying database interactions.
2. List some Entity Framework pros and cons.
Pros:
- Reduces boilerplate code by handling database interactions automatically.
- Supports LINQ for querying data.
- Auto migrations simplify database schema evolution.
- Improves productivity and rapid development.
Cons:
- Slower than raw ADO.NET for large-scale operations.
- Can be complex to debug generated queries.
- Less control over performance tuning and optimization.
3. Describe the architecture of the Entity Framework?
The architecture includes:
- Entity Data Model (EDM): Contains conceptual, storage, and mapping models.
- LINQ to Entities: Query language for working with entities.
- Entity SQL: A SQL-like query language for complex queries.
- Object Services: Handles object tracking and identity management.
- EntityClient: Converts LINQ or Entity SQL queries into SQL.
- ADO.NET Data Provider: Communicates directly with the database.
4. How does Entity Framework work?
It maps domain classes to a database schema, translates LINQ queries to SQL, tracks changes to objects, and saves those changes to the database.
5. How to retrieve data from the database using Entity Framework in MVC?
- Create an MVC project and install EF via NuGet.
- Define your model class and DbContext.
- Configure the connection string in web.config.
- Create a controller and inject your context.
- Retrieve and return data to a view.
6. What is DbContext and DbSet in Entity Framework?
DbContext is the primary class for database interaction. DbSet represents a collection of entities of a specific type, used for querying and saving.
7. What is the difference between ADO.NET and Entity Framework?
- ADO.NET: Manual coding, high performance, lower abstraction.
- Entity Framework: Higher abstraction, code-first/database-first approach, more development productivity.
8. What is the difference between LINQ and Entity Framework?
- LINQ: A query language used with various data sources, including EF.
- Entity Framework: An ORM that supports LINQ for querying databases.
9. Explain POCO classes in Entity Framework?
POCO stands for Plain Old CLR Object. These classes do not inherit from EF-specific base classes, allowing for clean separation and testing.
10. What are the various Entity Framework approaches?
- Database First
- Model First
- Code First
11. What is Code First approach in Entity Framework?
Code First allows developers to define models using C# or VB.NET classes and generate a database schema from those models.
12. What is Database First approach in Entity Framework?
Database First enables creation of EF models from an existing database using a visual designer (.edmx).
13. What is the Model First approach in Entity Framework?
Model First involves designing the database schema using a designer, which then generates the database and corresponding model code.
14. Which approach is best in Entity Framework?
It depends on the scenario:
- Database First: When a database already exists.
- Model First: When starting with a visual design.
- Code First: When starting with classes and object-oriented design.
15. What is a .edmx file in Entity Framework?
An .edmx file is an XML-based file used in Database/Model First approaches. It defines conceptual, storage, and mapping models, and is used by the EF designer.
16. How to handle concurrency in Entity Framework?
EF uses optimistic concurrency by default. To handle conflicts, use attributes like [Timestamp] and check for DbUpdateConcurrencyException when saving changes.
17. What is a navigation property in Entity Framework?
Navigation properties represent relationships between entities, enabling easy access to related data through object references or collections.
18. What types of loading are available in Entity Framework?
- Eager Loading: Loads related data immediately with the main entity.
- Lazy Loading: Loads related data only when accessed.
- Explicit Loading: Manually loads related data using the context.
19. Explain Pluralize and Singularize in Entity Framework?
EF uses pluralization and singularization for naming conventions when generating model classes and database tables, e.g., Student becomes Students table.
20. What is the difference between Entity Framework Core and Entity Framework 6?
Entity Framework Core is a lightweight, cross-platform, and more modular version of EF 6. EF Core supports more databases (including NoSQL), has better performance, and supports features like batching and shadow properties. However, EF 6 has broader feature coverage for older applications.
21. What are shadow properties in Entity Framework Core?
Shadow properties are not defined in your C# entity class but exist in the EF Core model. They are useful for tracking metadata like timestamps without cluttering your entity classes.
22. How do you configure relationships in Entity Framework?
Relationships can be configured using:
- Data Annotations (e.g., [ForeignKey])
- Fluent API in OnModelCreating() method
This allows you to define one-to-one, one-to-many, and many-to-many relationships.
23. How does migration work in Entity Framework Code First?
Migrations allow you to evolve the database schema over time:
- Use Add-Migration to scaffold a migration script.
- Use Update-Database to apply it.
- It supports version control for the schema.
24. How can you seed data using Entity Framework?
EF Core allows data seeding via the ModelBuilder.Entity().HasData() method during model configuration in OnModelCreating.
25. How do you log SQL queries generated by Entity Framework?
In EF Core, you can log queries using built-in logging: optionsBuilder.LogTo(Console.WriteLine) inside your DbContext configuration.
26. What is the difference between AsNoTracking and tracking queries?
AsNoTracking() returns entities not tracked by the context, which improves performance for read-only operations. Tracked queries keep a record of changes, allowing updates.
27. What is the role of Fluent API in Entity Framework?
Fluent API provides advanced configuration options for EF models that cannot be achieved with data annotations. It’s used inside OnModelCreating method in the DbContext.