Top NET Core Interview Questions for 2025

Question: What is ADO.NET?

Answer:

ADO.NET (ActiveX Data Objects .NET) is a set of classes in the .NET Framework that provides a comprehensive and efficient way to interact with data from different sources, such as databases, XML files, and other data services. It is the primary data access technology for interacting with relational databases in .NET applications.

ADO.NET is part of the System.Data namespace and is designed to enable the development of data-driven applications by providing a set of APIs for connecting to databases, retrieving and manipulating data, and executing commands.

---

Key Features of ADO.NET:

1. Disconnected Architecture:

   • ADO.NET operates on a disconnected model, meaning that after retrieving data from the database, you can work with it offline, i.e., without keeping an open connection to the database.
   • This is achieved through objects like DataSet and DataTable, which can hold data in memory and be updated independently of the database connection.

2. Support for Multiple Data Sources:

   • ADO.NET supports various data sources such as SQL Server, Oracle, MySQL, and any other data source that provides an OLE DB or ODBC interface.
   • It supports both SQL-based databases (using SqlConnection, SqlCommand, etc.) and non-SQL data sources.

3. Data Retrieval and Manipulation:

   • Data Providers: ADO.NET uses specific data providers for interacting with different databases (e.g., SqlDataAdapter for SQL Server, OleDbDataAdapter for OLE DB sources).
   • DataSet: A DataSet is an in-memory cache of data that can hold multiple tables, along with relationships and constraints, and is often used for disconnected data operations.
   • DataTable: A DataTable holds a single table of data in memory and allows for efficient querying and updating of data.

4. Command Execution:

   • ADO.NET provides the ability to execute various types of commands such as SQL queries, stored procedures, and DDL (Data Definition Language) commands. Commands can be executed synchronously or asynchronously.
   • It includes Command objects like SqlCommand, OleDbCommand, and DbCommand, which are used to execute SQL statements or stored procedures.

5. Data Binding:

   • ADO.NET provides support for data binding, allowing data from DataSet or DataTable to be bound to user interface controls like grids, lists, etc.

6. Transactions:

   • ADO.NET supports database transactions to ensure that a sequence of operations is either fully completed or rolled back. This is useful for maintaining data consistency.
   • Transactions are managed using the SqlTransaction object (or corresponding objects for other data providers).

---

Main ADO.NET Classes and Components:

1. Data Providers:

   • ADO.NET provides different data providers depending on the type of data source you’re working with. Each provider is made up of several core classes:

     • SqlDataProvider (for SQL Server):
       • SqlConnection: Used to establish a connection to the database.
       • SqlCommand: Used to execute SQL queries and stored procedures.
       • SqlDataReader: Used to read data from a database in a forward-only, read-only manner.
       • SqlDataAdapter: Used to fill a DataSet or DataTable with data from the database and update the database with changes from the DataSet.
     • OleDbDataProvider (for OLE DB data sources):
       • Similar to the SqlDataProvider but for OLE DB-compatible databases.
     • ODBC Data Provider:
       • Used for databases that support the ODBC interface (e.g., MySQL, PostgreSQL).

2. Disconnected Model:

   • DataSet: A container that can hold multiple DataTable objects and manage relationships between them.
   • DataTable: A single in-memory table of data. It can be used to manipulate and query data offline.
   • DataRelation: Used to represent relationships between DataTable objects in a DataSet.

3. Connected Model:

   • SqlConnection: Establishes a connection to a SQL Server database.
   • SqlCommand: Represents a SQL statement or stored procedure that can be executed against a database.
   • SqlDataReader: Provides a forward-only stream of data from a database. It is efficient for reading large amounts of data.
   • ExecuteReader, ExecuteScalar, and ExecuteNonQuery methods of SqlCommand are used for retrieving data, performing single value queries, and executing commands that don’t return data, respectively.

4. Data Binding:

   • ADO.NET supports data binding via controls like GridView, ListView, and DataGrid. These controls can be bound to DataSet or DataTable objects for displaying data.

---

Basic Workflow in ADO.NET:

1. Create a Connection: Establish a connection to the data source (e.g., SQL Server).

   SqlConnection connection = new SqlConnection("your_connection_string");
   connection.Open();

2. Create a Command: Define a SQL query or stored procedure to execute.

   SqlCommand command = new SqlCommand("SELECT * FROM Employees", connection);

3. Execute the Command:

   • To retrieve data, you can use SqlDataReader or SqlDataAdapter.

   Using SqlDataReader:

   SqlDataReader reader = command.ExecuteReader();
   while (reader.Read())
   {
       Console.WriteLine(reader["Name"].ToString());
   }
   reader.Close();

   Using SqlDataAdapter and DataSet (for disconnected operations):

   SqlDataAdapter adapter = new SqlDataAdapter(command);
   DataSet dataSet = new DataSet();
   adapter.Fill(dataSet, "Employees");

4. Manipulate Data: Modify data in the DataSet or DataTable (in disconnected mode), then update the database if needed.

   SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
   adapter.Update(dataSet, "Employees");

5. Close the Connection: Always close the connection when done.

   connection.Close();

---

Advantages of ADO.NET:

1. Performance: ADO.NET allows for efficient data access and manipulation with minimal overhead, especially in disconnected scenarios using DataSet or DataTable.
2. Scalability: The disconnected nature of ADO.NET enables large-scale data operations where the database connection can be opened, used, and closed quickly.
3. Flexibility: ADO.NET supports a wide variety of data sources (SQL databases, XML, ODBC, OLE DB) and is highly flexible for various data access scenarios.
4. Extensibility: Developers can create custom data providers or extend existing ones to support other data sources or formats.

---

Summary:

ADO.NET is a powerful set of libraries in .NET used for data access. It supports both connected and disconnected models for interacting with databases, allowing developers to retrieve, manipulate, and update data efficiently. ADO.NET provides a wide array of classes like SqlConnection, SqlCommand, SqlDataAdapter, DataSet, and DataTable to interact with databases in a flexible and efficient manner, making it essential for building data-driven applications.

Question: What are the benefits of using Entity Framework in .NET?

Answer:

Entity Framework (EF) is an Object-Relational Mapping (ORM) framework for .NET that allows developers to interact with databases using .NET objects, removing the need to write complex SQL queries. EF enables developers to work with databases in an object-oriented manner, making data manipulation and retrieval easier and more efficient.

Here are the key benefits of using Entity Framework in .NET:

---

1. Simplified Data Access

• Object-Relational Mapping (ORM): Entity Framework simplifies the interaction with relational databases by mapping database tables to C# classes. This allows developers to work with objects in code, rather than manually handling SQL queries or database schemas.
• Automatic Mapping: EF handles the mapping of entities (C# classes) to database tables, fields, and relationships, reducing the need for custom SQL queries or stored procedures.

Example:

var customers = context.Customers.ToList();

---

2. Strongly Typed Querying

• LINQ Support: Entity Framework integrates seamlessly with Language Integrated Query (LINQ), enabling developers to write type-safe queries using C# syntax. This improves code readability, reduces runtime errors, and provides IntelliSense support in IDEs like Visual Studio.
• With LINQ, developers can write database queries without writing raw SQL, which makes the code more maintainable and reusable.

Example:

var customers = context.Customers
                        .Where(c => c.City == "New York")
                        .ToList();

---

3. Reduced Boilerplate Code

• No Need for SQL: EF eliminates the need to manually write SQL queries or stored procedures for most CRUD (Create, Read, Update, Delete) operations. Developers can focus on business logic and let EF handle the low-level database interactions.
• Automatic SQL Generation: EF automatically generates SQL queries for data manipulation based on LINQ queries or method calls. This reduces repetitive code and ensures that database operations are executed in a consistent way.

Example (using SaveChanges to persist changes to the database):

context.SaveChanges();

---

4. Easier Database Schema Changes

• Migrations: EF provides migrations to handle changes in the database schema. With migrations, developers can easily evolve the database schema over time without manually updating the database.
• Migrations allow developers to add, remove, or modify database tables and columns, and then automatically synchronize these changes with the underlying database without losing data.

Example:

Add-Migration AddAgeToCustomer
Update-Database

---

5. Supports Multiple Database Providers

• Cross-Database Compatibility: Entity Framework supports multiple database providers out of the box, such as SQL Server, SQLite, MySQL, PostgreSQL, Oracle, and others.
• This makes it easy to switch between databases or build applications that can run on different database platforms.

Example (using SQL Server as the provider):

optionsBuilder.UseSqlServer("your_connection_string");

---

6. Change Tracking

• Automatic Change Tracking: EF automatically tracks changes to entities (objects) in memory. This means that when you modify an object, EF can automatically detect the changes and generate the appropriate SQL UPDATE statement when calling SaveChanges().
• This reduces the need for manual tracking of changes and ensures that only the changed data is updated in the database.

Example:

customer.Name = "Updated Name";
context.SaveChanges(); // EF will detect and save the changes to the database

---

7. Lazy Loading and Eager Loading

• Lazy Loading: EF supports lazy loading, which means related entities (such as navigation properties) are automatically loaded when they are accessed for the first time. This can help improve performance by only loading data when necessary.

Example (assuming Orders is a navigation property):

var customer = context.Customers.First();
var orders = customer.Orders.ToList();  // Lazy load related Orders

• Eager Loading: With eager loading, developers can explicitly load related entities in a single query, which reduces the number of database round-trips.

Example:

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

---

8. Better Performance with Optimized Queries

• Compiling Queries: EF can optimize queries by compiling them into reusable execution plans, reducing the overhead of parsing and compiling the same query repeatedly.
• EF Core: The newer version of Entity Framework, EF Core, comes with several performance improvements, including better query execution, better support for in-memory databases, and more efficient handling of large datasets.

---

9. Integrated Security

• SQL Injection Prevention: Since Entity Framework uses parameterized queries internally, it helps prevent SQL injection attacks. The framework ensures that input data is safely treated as parameters rather than raw SQL, making the application more secure.

Example:

var customers = context.Customers
                        .Where(c => c.City == userInput)
                        .ToList();

---

10. Rich Ecosystem and Community Support

• Microsoft Ecosystem: Entity Framework is fully supported by Microsoft and integrates well with other .NET technologies, such as ASP.NET Core, Azure, and more.
• Large Community: Being a widely used ORM in the .NET ecosystem, EF has a large community, plenty of resources, tutorials, and active forums for support.
• Third-party Libraries: Many third-party libraries and tools are designed to work with EF, such as performance monitoring tools, reporting libraries, and additional extensions.

---

11. Reduced Complexity with Complex Queries

• Complex Queries Made Easy: EF allows developers to write complex queries involving joins, groupings, and aggregations in a more readable and maintainable way using LINQ, without worrying about raw SQL syntax.
• EF can automatically generate complex SQL queries and execute them against the database, abstracting away much of the complexity.

Example:

var query = context.Customers
                   .Where(c => c.Orders.Any(o => o.Amount > 1000))
                   .ToList();

---

12. Better Code Maintenance

• Separation of Concerns: EF encourages the use of separation of concerns, allowing the data layer to be abstracted from business logic and UI layers. This leads to cleaner, more maintainable, and testable code.
• Model-First, Database-First, and Code-First: EF supports different approaches to developing your application, whether you prefer to define your database schema in the code, generate it from an existing database, or create it from models. This flexibility allows developers to choose the most suitable approach for their use case.

---

Summary of Key Benefits:

Benefit	Description
Simplified Data Access	Entity Framework allows for querying and manipulating data using objects, eliminating the need for SQL in most cases.
Strongly Typed Querying	EF integrates with LINQ, enabling type-safe queries and reducing runtime errors.
Reduced Boilerplate Code	No need to write repetitive SQL queries or manually map data between objects and database tables.
Migrations	EF provides migrations for easily evolving the database schema without data loss.
Cross-Database Compatibility	EF supports multiple database providers, making it easy to switch databases.
Change Tracking	EF automatically tracks changes to entities, making updates to the database easier and more efficient.
Lazy and Eager Loading	EF supports lazy and eager loading to optimize performance when dealing with related entities.
Optimized Queries	EF can generate optimized SQL queries, improve performance, and reduce database round-trips.
SQL Injection Protection	EF prevents SQL injection attacks by using parameterized queries.
Community Support	EF benefits from strong support within the .NET ecosystem, including active community forums, tutorials, and resources.
Complex Queries Simplified	Complex queries involving joins, groupings, and filters can be written easily using LINQ.
Maintainable Code	Entity Framework promotes clean, modular code that is easier to maintain, test, and evolve.

---

Conclusion:

Entity Framework is a powerful ORM tool in .NET that simplifies data access, improves productivity, and reduces the need for raw SQL in your applications. It enhances maintainability, security, and performance while providing a flexible approach to database management. Whether you’re building small applications or large-scale systems, EF provides a robust framework for handling your data access needs in a clean and efficient way.

Read More

If you can’t get enough from this article, Aihirely has plenty more related information, such as .NET interview questions, .NET interview experiences, and details about various .NET job positions. Click here to check it out.