here's a list of common Entity Framework interview questions along with answers tailored for ASP.NET MVC 5:
1. What is Entity Framework (EF)?
Answer: Entity Framework (EF) is an Object-Relational Mapping (ORM) framework provided by Microsoft. It enables developers to work with relational data using domain-specific objects, eliminating the need for most of the data-access code that developers usually need to write.
2. What are the advantages of using Entity Framework?
Answer:
- Reduced development time: EF automates a lot of repetitive tasks, such as creating SQL queries and mapping database tables to classes, which speeds up the development process.
- Improved productivity: EF provides a strongly-typed query language (LINQ) that allows developers to write queries using C# or VB.NET syntax, resulting in fewer errors and increased productivity.
- Database independence: EF allows developers to work with different database providers (SQL Server, MySQL, SQLite, etc.) without changing the application code significantly.
- Easy maintenance: EF simplifies code maintenance by allowing developers to work with domain-specific objects rather than dealing with low-level SQL queries.
3. What are the different approaches to database interaction in Entity Framework?
Answer:
- Code First: Developers define the domain model using classes and relationships, and EF creates the database schema based on these classes.
- Database First: Developers start with an existing database schema, and EF generates the corresponding classes and relationships based on the database schema.
- Model First: Developers create the domain model using an Entity Data Model (EDM) designer, and EF generates the database schema based on the model.
4. Explain Code First approach in Entity Framework.
Answer: In the Code First approach, developers define the domain model using plain old CLR objects (POCO) and configure the mapping between classes and database tables using data annotations or Fluent API. EF then generates the database schema based on the classes and relationships defined in the code.
5. How can you enable Code First Migrations in Entity Framework?
Answer: To enable Code First Migrations, you need to run the following commands in the Package Manager Console:
Add-Migration InitialCreate
Update-Database
These commands enable Migrations, create an initial migration named "InitialCreate," and apply the migration to the database.
6. Explain Lazy Loading and Eager Loading in Entity Framework.
Answer:
- Lazy Loading: Lazy loading is a feature of EF that automatically loads related entities from the database when you access a navigation property. It defers the loading of related entities until they are actually needed.
- Eager Loading: Eager loading is the opposite of lazy loading. It allows you to load related entities along with the main entity in a single query using the
Include()method orIncludeextension method.
7. What is the purpose of DbContext class in Entity Framework?
Answer: The DbContext class in Entity Framework represents a session with the database, allowing you to query and save data. It acts as a bridge between your domain classes and the database, providing APIs to interact with the database, such as querying data using LINQ, adding, updating, and deleting entities, and managing transactions.
8. Explain how to execute raw SQL queries in Entity Framework.
Answer: You can execute raw SQL queries in Entity Framework using the SqlQuery() method or Database.SqlQuery() method. Here's an example:
var customers = context.Database.SqlQuery<Customer>("SELECT * FROM Customers").ToList();
9. What is the purpose of DbSet<TEntity> in Entity Framework?
Answer: DbSet<TEntity> represents a collection of entities of a specific type in the context. It provides APIs to query, add, update, and delete entities of the specified type.
10. How can you improve Entity Framework performance?
Answer: Some ways to improve Entity Framework performance include:
- Use eager loading: Fetch related entities in a single query using the
Include()method to avoid the N+1 query problem. - Use compiled queries: Compile LINQ queries using the
Compile()method to improve query execution performance. - Optimize database schema: Design efficient database schemas, create indexes on frequently queried columns, and optimize SQL queries to improve overall performance.
- Disable change tracking: Disable change tracking for read-only scenarios using the
AsNoTracking()method to reduce overhead. - Batch updates and deletes: Use batch updates and deletes for bulk operations to minimize round trips to the database.
These are some of the commonly asked Entity Framework interview questions for ASP.NET MVC 5. Make sure to understand the concepts thoroughly and be prepared to discuss your experience with Entity Framework in real-world scenarios.
11. What is the difference between DbSet.Find() and DbSet.SingleOrDefault()?
Answer:
DbSet.Find(): This method is used to find an entity with the given primary key values. It first checks if the entity is already being tracked by the context. If yes, it returns the entity from the context. Otherwise, it queries the database to find the entity by its primary key values.DbSet.SingleOrDefault(): This method is used to find a single entity based on a predicate. If there is more than one matching entity, or if no entity matches the predicate, it throws an exception. It's useful when you expect exactly one entity to match the criteria.
12. Explain the EntityState enum in Entity Framework.
Answer: The EntityState enum in Entity Framework represents the state of an entity being tracked by the context. It can have the following values:
- Unchanged: The entity has not been modified since it was queried from the database.
- Added: The entity is newly created and has been added to the context but not yet saved to the database.
- Modified: The entity has been modified and needs to be updated in the database.
- Deleted: The entity has been marked for deletion and will be removed from the database when
SaveChanges()is called. - Detached: The entity is not being tracked by the context.
13. How can you execute stored procedures using Entity Framework?
Answer: You can execute stored procedures using the DbContext.Database.ExecuteSqlCommand() method. Here's an example:
int rowsAffected = context.Database.ExecuteSqlCommand("EXEC sp_UpdateEmployee @EmployeeId, @Name",
new SqlParameter("@EmployeeId", employeeId),
new SqlParameter("@Name", newName));
You can also map stored procedures to entity operations using the Database.SqlQuery<T>() method or by using Entity Framework Code First Migrations.
14. What are navigation properties in Entity Framework?
Answer: Navigation properties in Entity Framework represent relationships between entities. They allow you to navigate from one entity to related entities. For example, in a one-to-many relationship between Order and OrderDetail entities, the Order entity may have a navigation property called OrderDetails to navigate to the collection of related OrderDetail entities.
15. Explain the purpose of migrations in Entity Framework.
Answer: Migrations in Entity Framework allow you to manage changes to the database schema over time. They enable you to create and apply incremental changes to the database schema, such as adding or modifying tables, columns, or constraints, while preserving existing data. Migrations help ensure that the database schema stays in sync with the model classes in your application.
16. How can you configure database connection strings in Entity Framework?
Answer: Database connection strings in Entity Framework can be configured in the web.config or app.config file of your application. You can use the <connectionStrings> element to define connection strings for different environments (e.g., development, testing, production). Here's an example:
<connectionStrings>
<add name="MyDbContext" connectionString="Data Source=ServerName;Initial Catalog=DatabaseName;Integrated Security=True;" providerName="System.Data.SqlClient" />
</connectionStrings>
You can then reference this connection string by name in your DbContext class constructor.
17. How can you handle concurrency conflicts in Entity Framework?
Answer: Entity Framework provides optimistic concurrency control to handle concurrency conflicts. When updating an entity, EF checks if the entity's original values in the database match the current values in memory. If they don't match, it throws a DbUpdateConcurrencyException, indicating that another user has modified the entity since it was loaded. You can handle this exception by reloading the entity from the database, applying your changes, and then saving again.
18. Explain how to enable logging in Entity Framework.
Answer: You can enable logging in Entity Framework to capture SQL queries and other runtime information. You can configure logging using the DbContext.Database.Log property or by configuring a logging provider such as Serilog or NLog. Here's an example:
context.Database.Log = Console.Write; // Log to console
This will print the generated SQL queries to the console.
19. What is the purpose of the Entity Framework Database First approach?
Answer: The Database First approach in Entity Framework is used when you already have an existing database schema and want to generate entity classes and DbContext from it. It involves reverse-engineering the database schema to generate the corresponding code-first model classes, which can then be used to query and manipulate data.
20. How can you configure relationships between entities in Entity Framework?
Answer: Relationships between entities in Entity Framework can be configured using data annotations or Fluent API. You can specify navigation properties, foreign keys, and multiplicity (one-to-one, one-to-many, many-to-many) using attributes like [ForeignKey], [InverseProperty], [Required], etc., or by using methods like HasMany(), WithOne(), HasForeignKey(), etc., in the Fluent API configuration.
These are some Entity Framework interview questions that cover various aspects of working with Entity Framework in ASP.NET MVC 5 applications. Understanding these concepts will help you prepare for interviews and effectively use Entity Framework in your projects.