[Interview Questions Analysis] .NET Practical Interview Questions and Answers with AI Supplement for Comparative Learning

In the [DotNet 开发跳槽] official account, the author has prepared a batch of practical .NET interview questions for everyone:

In this article, the author has supplemented some detailed answers using AI. These interview questions cover various aspects of .NET development, including the .NET framework, C# language, ASP.NET, ADO.NET, databases, etc. By comparing and learning, we can better understand and master these knowledge points.

During the interview process, it is very important to master and understand these interview questions. Interviewers usually use these questions to examine our understanding and practical experience of .NET development. Therefore, by learning these interview questions, we can better prepare for interviews and improve our competitiveness.

Interview Question Directory:

What are CTS, CLS, and CLR
Comparison between CLR technology and COM technology
How does JIT work
How to put an assembly into the GAC
Differences between value types and reference types
What is the difference between string and String in C#
Briefly describe the characteristics and differences between stack and heap in .NET
The operating mechanism of GC in .NET
Briefly describe the concepts of override, overload, and hiding in C#
How to declare a class that cannot be inherited in C#
Is int[] a reference type or a value type
Explain the basic principles of generics
What is the role of the Serializable attribute
How to customize the serialization and deserialization process
How to use the IFormattable interface to achieve formatted output
What timer types does .NET provide
What are the similarities and differences of the three comparison methods defined in System.Object
Please explain the basic principles of delegates
What is the difference between delegate callback static methods and instance methods
What is chained delegate
Please explain the basic usage of events
Please explain the basic principles of reflection and the cornerstone of its implementation
How to use reflection to implement the factory pattern
How to save Type, Field, and Method information with minimal memory cost
What is a thread
How to use .NET's thread pool
What is the role of the lock keyword in C#
Please explain how ASP.NET runs
What is the difference between GET request and POST request
Introduce the page lifecycle of ASP.NET
List several methods to achieve page redirection
How to prevent SQL injection attacks
What data sources does ADO.NET support
Please briefly describe the mechanism of the database connection pool
What attributes can a connection string contain
What is a strongly typed DataSet
What is XML
How to use namespaces in XML
How to validate the format of an XML document in .NET
What is XSLT and what is the role of XSLT
How to use XSLT documents in code
Please briefly describe the SOAP protocol
How to create a Web Service in .NET
How to generate a Web Service proxy type
How to improve the reuse rate of connections in the connection pool
What two ways does ADO.NET support to access relational databases
What are relational databases and non-relational databases
What storage methods does Session have, what are the differences between them, and how to configure them
Please briefly describe the function and implementation mechanism of ViewState
What is row-to-column and column-to-row in databases
What is the relationship between ADO.NET and ORM

1. CTS, CLS, and CLR

CTS (Common Type System) is a specification in .NET, a common language system that defines all supported data types and operations, ensuring interoperability between different languages.

CLS (Common Language Specification) is a subset of CTS, defining a minimal set of rules and conventions to ensure that code written in different languages can call each other.

CLR (Common Language Runtime) is the core component of .NET, responsible for compiling .NET code into executable code and executing it, providing memory management, security, exception handling, and other functions.

Detailed explanation: Interview Must-Have: What do CTS, CLS, and CLR mean in .NET?

2. Comparison between CLR technology and COM technology

CLR technology and COM technology are both used for component-based development, but there are some differences. CLR is a technology for managed code, providing automatic memory management, type safety, exception handling, etc., and supports multi-language development. It allows code written in different languages to execute in a unified environment.

COM is a technology for unmanaged code, providing a mechanism for component-based development, but requires manual memory management and exception handling, and only supports C++ and COM-compatible languages.

COM requires manual memory management, while CLR provides automatic garbage collection.

CLR provides powerful security and code access permission management, while COM has weaker security.

CLR is language-neutral and supports multiple languages, while COM is more inclined to use C++.

CLR uses metadata-based assemblies, while COM uses the registry for component registration and lookup.

3. How does JIT work

JIT: Just-In-Time compilation is an important component of the CLR, responsible for compiling IL code (Intermediate Language) into native machine code. JIT compiles IL code into machine code at runtime as needed to improve execution efficiency.

This is the basic way .NET runs executable programs, meaning that the corresponding IL code is compiled into native instructions only when it needs to be executed. The input to JIT is IL code, and the output is native code. Therefore, some encryption software hooks JIT to encrypt IL while ensuring the program runs normally. Compared with interpreted code, JIT execution efficiency is much higher.

When a .NET program starts, the IL code is first interpreted and executed by the CLR. However, to improve execution efficiency, the CLR compiles the IL code into native code piece by piece and caches it for subsequent use.

JIT compilation is a form of lazy compilation, only compiling a piece of IL code when it actually needs to be executed.

There are three modes of JIT:

Pre-compilation mode (Ngen), which pre-compiles IL code into native machine code;
Lazy compilation mode (JIT-Compiler), which compiles IL code on demand at runtime;
Mixed mode, which uses both pre-compilation and lazy compilation.

Detailed explanation: Understanding CLR and JIT, .NET Disassembly Learning

4. How to put an assembly into the GAC

Putting an assembly into the GAC (Global Assembly Cache) enables global sharing and version management of the assembly. In simple terms, it is a place to store various DLLs needed under the .NET platform.

You can use the Gacutil tool to install an assembly into the GAC (gacutil /i YourAssembly.dll), or manually copy the assembly to the GAC directory (usually located at C:\Windows\Assembly).

Alternatively, you can use .NET code to install it, and it can also be uninstalled after installation.

When referencing an assembly in the GAC in a program, you can directly use the assembly name without specifying the full path.

5. Differences between value types and reference types

Value types and reference types are two basic data types in .NET.

Value types are stored on the stack, including simple types such as integers, floating-point numbers, characters, etc. Their values are stored directly in the variable.

Reference types are stored on the heap, including complex types such as classes, interfaces, delegates, etc. The variable stores a reference to the object. The reference is stored on the stack or somewhere on the heap, and the actual object is stored on the heap.

Assignment of value types copies the actual value to the new variable, while assignment of reference types copies the reference, pointing to the same object.

Value types are passed by value, while reference types are passed by reference.

Each assignment of a value type performs a field-by-field copy, while assignment of a reference type is just passing the pointer, though it also creates a new pointer instance.

Detailed explanation: C# Basics - In-depth Understanding of Value Types and Reference Types

6. What is the difference between string and String in C#

In C#, string is a C# keyword, representing the string type in .NET;

String is an alias for the System.String class, meaning string is an alias for String, and there is no substantive difference.

String is the old name from .NET Framework. It was introduced in C# 1.0 and was replaced by string in C# 2.0. In actual use, they can be interchanged without any substantive difference.

7. Characteristics and differences between stack and heap in .NET

In .NET, heap and stack are two different memory allocation methods.

The heap is used to store objects of reference types, with memory allocation and release managed by the garbage collector. Memory allocated by functions like new, malloc is on the heap.

The stack is used to store variables of value types and method call context information, with memory allocation and release automatically managed by the compiler. Variables defined within a function body are typically on the stack.

Heap allocation is slower but allows dynamic memory allocation and release. It is unordered, a discontinuous memory area controlled and released by the user. If the user does not release it, when the memory reaches a certain threshold, it is reclaimed by the garbage collector (GC).

Stack allocation is faster but fixed in size and has a short lifetime. It maintains storage order with a last-in-first-out principle. It is a continuous memory area automatically allocated and maintained by the system. Stack memory does not need to be managed by us and is not affected by GC. When the top element of the stack is used, it is immediately released. The heap requires GC cleanup. When using reference types, operations are generally on the pointer rather than the reference type object itself. However, value types operate on themselves.

The lifetime of stack variables is determined by method calls, while objects on the heap have a longer lifetime managed by the garbage collector.

Detailed explanation: Basic Interview Must-Have: Differences and Analysis of Stack and Heap in C#

8. The operating mechanism of GC in .NET

GC stands for Garbage Collection, a part of the CLR, an important part of the core .NET mechanism. It is an automatic memory management mechanism that periodically checks for objects no longer in use and frees their occupied memory. The garbage collector tracks object references. When an object is no longer referenced, the garbage collector marks it as garbage and reclaims its memory at an appropriate time. The garbage collector uses different algorithms and strategies, such as mark-sweep, copying, mark-compact, etc.

The basic working principle is to traverse objects on the managed heap, mark which objects are in use (those not in use are called garbage), then move reachable objects to a contiguous address space (also called compaction), and reclaim the memory of all remaining useless objects.

Detailed explanation: .NET Special Topic Interview Questions: GC and Memory Management (Including In-depth Analysis)

9. Concepts of override, overload, and hiding

In C#, override means a derived class reimplements a virtual method of the base class.

Overload means defining multiple methods with the same name but different parameter lists within the same class, to adapt to different needs. It refers to "covering", meaning a subclass covers a method of the parent class. Objects of the subclass can no longer access that method in the parent class.

Hiding (new) means a subclass hides a method of the parent class. Of course, through a certain conversion, the method in the parent class can be accessed from the subclass object. If an object declared with the subclass type calls the hiding method, it will call the subclass's method; if declared with the parent class type, it will call the parent class's hiding method. [Reference: C#—Hidden Methods]

Override and overload are both forms of polymorphism, while hiding hides the members of the base class.

Detailed explanation: Interview Must-Have: The Difference Between Overload and Override in C# Polymorphism

10. How to declare a class that cannot be inherited in C#

In C#, you can use the sealed keyword to declare a class that cannot be inherited. When a class is declared as sealed, other classes cannot inherit from it.

sealed class MySealedClass { }

11. Is int[] a reference type or a value type

int[] is a reference type because it is an array type, and array types are reference types stored on the heap. The array variable itself is stored on the stack, pointing to the data on the heap.

12. Explain the basic principles of generics

Generics are a feature in .NET that allows specifying type parameters at compile time to achieve type safety and code reuse. The basic principle of generics is to generate specific type code through compile-time type checking and type inference. At runtime, generic code is instantiated into specific types to improve execution efficiency.

Generics allow writing code that works with different data types without writing separate code for each type.

When using generics, you can define a template (class, interface, method, etc.) where some types can be specified at actual use.

Detailed explanation: The Principles of C# Generics You Didn't Know

13. What is the role of the Serializable attribute

The Serializable attribute is used to mark a class that can be serialized, meaning its objects can be converted into a byte stream for storage or transmission. The Serializable attribute tells the compiler and runtime environment that instances of the class can be serialized and deserialized.

Serialization converts an object into a byte stream, and deserialization converts the byte stream back into an object.

14. How to customize the serialization and deserialization process

Customizing the serialization and deserialization process can be achieved by implementing the ISerializable interface. The ISerializable interface defines two methods: GetObjectData for serializing object data into a byte stream, and a constructor for deserialization.

[Serializable]
public class CustomSerializableClass : ISerializable
{
    public string Name { get; set; }
    public int Age { get; set; }

    // Implement ISerializable interface method
    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("Name", Name);
        info.AddValue("Age", Age);
    }
    // Constructor for deserialization
    protected CustomSerializableClass(SerializationInfo info, StreamingContext context)
    {
        Name = info.GetString("Name");
        Age = info.GetInt32("Age");
    }
}

15. How to use the IFormattable interface to achieve formatted output

Using the IFormattable interface can achieve formatted output. The IFormattable interface defines a method ToString that accepts a format string and a format provider as parameters, converting the object to a string according to the format string and format provider.

Reference: IFormattable Interface (System) | Microsoft Learn

16. What timer types does .NET provide

.NET provides several timer types, including System.Timers.Timer, System.Threading.Timer, and System.Windows.Forms.Timer.

System.Timers.Timer

This is an event-based timer in the System.Timers namespace. It is a wrapper around System.Threading.Timer and is more suitable for multi-threaded environments because the callback method executes on the thread that created the timer by default. It supports single or periodic task scheduling.

System.Threading.Timer

This is a thread-based timer in the System.Threading namespace. It executes a callback method at specified intervals and can implement single or periodic task scheduling. Note that the callback method executes on another thread, so you need to handle thread synchronization carefully in the callback method.

System.Windows.Forms.Timer

This is a timer for Windows Forms applications in the System.Windows.Forms namespace. It is mainly used to perform periodic UI updates in Windows Forms applications, and the callback method executes on the UI thread.

System.Diagnostics.Stopwatch

This is a high-precision timer in the System.Diagnostics namespace. Although not a typical timer, it is used to measure the execution time of code segments and can help with performance analysis.

System.Threading.Tasks.Task.Delay

This is not a traditional timer but an asynchronous delay implemented via the Task.Delay method. It allows waiting for a period before performing asynchronous operations and can be used to implement delayed tasks.

Detailed explanation: C# 3 Timer Usages

17. What are the similarities and differences of the three comparison methods defined in System.Object

In System.Object, three comparison methods are defined: Equals(object), Equals(object, object), and ReferenceEquals(object, object).

All three methods are used to compare whether two objects are equal. However, their comparison methods differ.

Equals(object) is a virtual method that can be overridden by subclasses. It compares whether the values of two objects are equal.

Equals(object, object) is a static method that cannot be overridden. It compares whether the references of two objects are equal.

ReferenceEquals(object, object) is a static method that cannot be overridden. It compares whether the references of two objects point to the same object.

18. Please explain the basic principles of delegates

Delegates in C# are similar to function pointers in C or C++. A delegate is a reference type variable that holds a reference to a method. The reference can be changed at runtime. It is essentially a class that defines the type of a method, allowing a method to be passed as a parameter to another method. This is a way to dynamically assign a method to a parameter.

A delegate is a reference type used to encapsulate a call to a method, allowing methods to be passed as parameters in a manner similar to function pointers. A delegate contains a reference to a method and an optional target object. When the delegate is invoked, it actually calls the method referenced by the delegate.

The basic principle of a delegate is to invoke a method through a delegate instance, which contains the method reference and the context information for the call.

19. What is the difference between delegate callback static methods and instance methods

The difference between a delegate callback to a static method and an instance method lies in the way they are invoked. When a delegate calls a static method, the static method can be called directly using the class name; when a delegate calls an instance method, an instance object must be created first, and then the instance method is called using the instance object.

// Pseudocode for reference only
// Delegate callback to static method
Action<int> myAction = MyStaticMethod;
myAction(10);

// Delegate callback to instance method
MyClass myObject = new MyClass();
Action<MyClass> myAction2 = myObject.MyInstanceMethod;
myAction2(myObject);

20. What is chained delegate

Chained delegate refers to linking multiple delegate objects together to form a delegate chain. When a chained delegate is invoked, each delegate object is called in sequence until a delegate object returns a non-null value or all delegate objects have been called. Chained delegates can be used to implement event handler chains, asynchronous operation chains, and other complex tasks.

In C#, you can use the + operator to chain delegates. For example, the following code chains two delegates together:

Action<int> myAction1 = (x) => Console.WriteLine(x);
Action<int> myAction2 = (x) => Console.WriteLine(x * x);
Action<int> myChainedAction = myAction1 + myAction2;
myChainedAction(10); // Output: 10 100

21. Please explain events and their basic usage

An event is a class member that allows a class to notify other classes or code when a specific situation occurs.

When defining an event, you need to use the delegate keyword to declare a delegate type, and then define an event member.

Use the += operator to add a subscriber's method to the event's delegate chain. When the event is triggered, the methods in the delegate chain will be called.

Detailed explanation: C# Delegate and Event Knowledge Points Every .NET Developer Should Master

22. Please explain the basic principles of reflection and the cornerstone of its implementation

Reflection is a mechanism in .NET used to obtain and manipulate type information at runtime.

Reflection is an important feature of the .NET platform, allowing you to obtain and manipulate information about assemblies, types, members, etc. at runtime.

The basic principle of reflection is to describe the structure of a type through metadata. At runtime, this metadata can be accessed to obtain detailed information about the type.

The cornerstone of reflection is metadata, which is part of the assembly and contains descriptive information about types, members, methods, etc. This allows the program to understand its own structure and composition at runtime.

23. How to use reflection to implement the factory pattern

First, understand how the factory pattern is implemented: the factory pattern replaces the instantiation of classes. Using reflection to implement the factory pattern allows creating object instances based on a specific class name or condition without explicitly specifying the instantiation of each object (new object).

using System;

// Define an interface
public interface IVehicle
{
    void Move();
}

// Two classes implementing IVehicle interface
public class Car : IVehicle
{
    public void Move()
    {
        Console.WriteLine("Car is moving");
    }
}

public class Bike : IVehicle
{
    public void Move()
    {
        Console.WriteLine("Bike is moving");
    }
}

// Factory class, using reflection to create object instances based on class name
public class VehicleFactory
{
    public IVehicle CreateInstance(string vehicleType)
    {
        Type type = Type.GetType(vehicleType); // Get the type
        if (type == null || !typeof(IVehicle).IsAssignableFrom(type))
        {
            throw new ArgumentException("Invalid vehicle type");
        }

        // Create an instance
        IVehicle vehicle = (IVehicle)Activator.CreateInstance(type);
        return vehicle;
    }
}

// Main call
#region
// Factory class instance
VehicleFactory factory = new VehicleFactory();

// Create instances of different types through the factory class
IVehicle car = factory.CreateInstance("Car");
IVehicle bike = factory.CreateInstance("Bike");

car.Move();  // Output: Car is moving
bike.Move(); // Output: Bike is moving

#endregion

24. How to save Type, Field, and Method information with minimal memory cost

Use lightweight structures like DynamicMethod or DynamicType in System.Reflection.Emit to save Type, Field, and Method information, creating and manipulating types with minimal memory overhead.

25. What is a thread

A thread is the smallest unit of program execution and the basic unit for task scheduling by the operating system. A process can contain multiple threads, each with its own execution path and execution state. Threads can execute concurrently, improving program execution efficiency. In .NET, the System.Threading namespace provides support for threads.

26. How to use .NET's thread pool

The thread pool allows reusing threads to improve performance and reduce the overhead of creating and destroying threads. You can use the ThreadPool.QueueUserWorkItem method to queue work items to the thread pool, which are then executed by threads in the pool. You can use the ThreadPool class to use .NET's thread pool.

 static void Main()
 {
     // Queue a work item to the thread pool
     ThreadPool.QueueUserWorkItem(DoWork, "Hello ThreadPool!");
     ThreadPool.QueueUserWorkItem(DoWork, "Hello ThreadPool2!");
     // Main thread continues with other work
     Console.WriteLine("Welcome to the official account [dotnet开发跳槽].");
     // Prevent console from closing immediately
     Console.ReadLine();
 }

static void DoWork(object state)
{
    // Work method executed by a thread from the thread pool
    string message = (string)state;
    Console.WriteLine($"ThreadPool work: {message}");
}

27. What is the role of the lock keyword in C#

Thread safety is important. The lock keyword is used to ensure safe access to shared resources in a multi-threaded environment. It protects a block of code by acquiring a mutual-exclusion lock on an object, allowing only one thread to enter the critical section until the thread releases the lock. The lock keyword ensures that only one thread can access the locked code block at a time, preventing data inconsistency caused by multiple threads accessing shared resources simultaneously.

28. Please explain how ASP.NET runs

ASP.NET runs on a web server, providing web services by processing HTTP requests and generating HTTP responses. ASP.NET can run in out-of-process or in-process modes, including IIS process hosting mode and self-hosting mode.

What about ASP.NET Core?

ASP.NET Core can also run on a web server, providing web services by processing HTTP requests and generating HTTP responses. Unlike traditional ASP.NET, ASP.NET Core is cross-platform and can run on Windows, Linux, macOS, and other operating systems.

ASP.NET Core can run in out-of-process or in-process modes. In out-of-process mode, ASP.NET Core applications run in a separate process and communicate with the web server over HTTP. Common web servers include IIS, Nginx, and Apache.

In in-process mode, ASP.NET Core applications are embedded directly into the web server process, sharing the same process space. In this mode, ASP.NET Core applications can handle requests more efficiently, reducing inter-process communication overhead.

ASP.NET Core also supports self-hosting mode, where the application runs directly as a standalone console application without relying on any web server. In self-hosting mode, ASP.NET Core applications can use Kestrel as the built-in web server or other third-party web servers.

In summary, ASP.NET Core can run in out-of-process or in-process modes and supports self-hosting mode, allowing you to choose the appropriate running method based on specific needs.

29. What is the difference between GET request and POST request

GET and POST requests are two common HTTP request methods. The difference is not significant, mainly in data transmission. GET requests append request parameters to the URL in plain text, suitable for retrieving data; POST requests place request parameters in the request body, which is more secure and has no length limit, suitable for submitting data. GET request parameters have a length limit, while POST request parameters have no length limit.

The length limit for HTTP GET query parameters varies among different browsers. Here are some common browser limits:

Internet Explorer: Internet Explorer 9 and below have a limit of 2,083 characters.
Microsoft Edge: Microsoft Edge has a limit of 8,192 characters.
Chrome: Chrome has a limit of 8,192 characters.
Firefox: Firefox has a limit of 65,536 characters.
Safari: Safari has a limit of 80,000 characters.

Note that these limits refer to the length of the query parameters, excluding other parts of the URL (such as protocol, domain name, path, etc.). Additionally, different browser versions may vary; the above limits are for reference. If you need to pass longer query parameters, consider using a POST request or placing parameters in the request body.

30. Introduce the page lifecycle of ASP.NET

The page lifecycle of ASP.NET includes multiple stages, such as page initialization, page loading, page rendering, event handling, page unloading, etc. In each stage, ASP.NET calls corresponding event handling methods, and developers can write their own code in these methods to implement specific functions.

31. List several methods to achieve page redirection

Traditional MVC projects use these methods; new projects generally separate read and write. Methods to achieve page redirection include: Response.Redirect, Server.Transfer, Server.Execute, using hyperlinks or button control navigation, using JavaScript's window.location method, etc.

32. How to prevent SQL injection attacks

Nowadays, ORM is commonly used, and this issue rarely occurs. To prevent SQL injection attacks, you can use parameterized queries or stored procedures to perform database operations. Parameterized queries pass user input data as parameters to the database, rather than concatenating user input directly into SQL statements. Validate and filter input data to prevent malicious injection of SQL code. Stored procedures encapsulate SQL statements in the database and can pass user input data through parameters.

33. What data sources does ADO.NET support

If ADO.NET continues to develop, the supported data sources will be unlimited. ADO.NET supports multiple data sources, including SQL Server, Oracle, OLEDB, ODBC, and XML.

34. Please briefly describe the mechanism of the database connection pool

The database connection pool is a mechanism for managing database connections. It creates a certain number of database connections when the application starts and saves them in the pool. When the application needs a database connection, it obtains an available connection from the pool. After use, the connection is returned to the pool instead of being closed. This reduces the time overhead of opening and closing connections, improving connection reuse and performance.

35. What attributes can a connection string contain

A connection string can contain multiple attributes, such as data source, username, password, connection timeout, etc. Common connection string attributes include: Data Source, Initial Catalog, User ID, Password, Connect Timeout, etc., depending on the database and provider being connected.

36. What is a strongly typed DataSet

A strongly typed DataSet is a DataSet whose structure is known at design time. It is created using Visual Studio's Dataset Designer and provides compile-time type checking and IntelliSense support. In a strongly typed DataSet, the types of tables and columns are explicitly specified, rather than using a generic Object type.

37. What is XML

XML (eXtensible Markup Language) is a markup language used to store and transmit data. It uses tags to describe the structure and content of data, with self-descriptive and extensible characteristics.

38. How to use namespaces in XML

Namespaces in XML are used to avoid conflicts between element and attribute names. You can use the xmlns attribute to define a namespace and use a prefix to reference elements and attributes within that namespace.

39. How to validate the format of an XML document in .NET

You can use an XML Schema Definition (XSD) file to validate an XML document, or use the XmlReader class, or XmlDocument class to validate the format of an XML document.

The XmlReader class provides a streaming way to read and validate XML documents. You can specify validation options by setting properties of XmlReaderSettings.

The XmlDocument class provides a DOM way to read and validate XML documents. You can specify validation options by setting properties of XmlValidatingReader.

40. What is XSLT and what is the role of XSLT

XSLT (eXtensible Stylesheet Language Transformations) is used to transform one XML document into another XML document, HTML page, or other text format. It is an XML-based transformation language. XSLT defines templates and rules to transform and process XML documents, commonly used to convert XML documents into HTML, PDF, and other formats.

41. How to use XSLT documents in code

Use classes in the .NET Framework, such as XslCompiledTransform or XmlDocument, to load an XSLT document and then apply it to transform XML data. Use the Transform method to convert an XML document into another format.

42. Please briefly describe the SOAP protocol

SOAP (Simple Object Access Protocol) is a communication protocol for exchanging structured information. It uses XML format to encapsulate and transmit data, allowing communication between network-based services and supporting interoperability between different environments and languages.

43. How to create a Web Service in .NET

You can use ASP.NET's WebService class to create a Web Service. Define public methods in the Web Service class and mark them with the WebMethod attribute so that they can be called via HTTP requests.

44. How to generate a Web Service proxy type

You can use the wsdl.exe tool or Visual Studio's "Add Service Reference" feature to generate a Web Service proxy type. The wsdl.exe tool generates proxy classes based on the WSDL document of the Web Service, while the "Add Service Reference" feature generates proxy classes based on the metadata of the Web Service. The generated proxy classes can be used to call methods of the Web Service.

45. How to improve the reuse rate of connections in the connection pool

Answer: The following methods can improve the reuse rate of connections in the connection pool:

Set connection pool parameters reasonably: According to application requirements, set parameters such as maximum connections, minimum connections, and connection timeout. Reasonable parameter settings can avoid excessive creation and destruction of connections in the pool, improving reuse rate.
Use the release mechanism of connections in the pool: When using connections from the pool, releasing connection resources promptly is important. Use the using statement or manually call the Close method of the connection to release resources, ensuring the connection can return to the pool quickly for other requests.
Avoid holding connections for a long time: When using a connection, minimize the time the connection is held. Release the connection as soon as possible after completing database operations, avoiding long occupation and improving availability and reuse.
Use connection string connection pool properties: The connection string can set connection pool-related properties, such as maximum connections and connection timeout. Setting these properties appropriately can control the number and lifecycle of connections in the pool, improving reuse rate.

46. What two ways does ADO.NET support to access relational databases

Answer: ADO.NET supports accessing relational databases through two providers:

SQLClient provider: The SQLClient provider is for accessing Microsoft SQL Server databases. It provides classes and methods for connecting, executing SQL statements, and processing results, allowing convenient interaction with SQL Server.
OLEDB provider: The OLEDB provider is a universal data access interface that can access various types of relational databases. It provides classes and methods for connecting, executing SQL statements, and processing results, adapting to different databases through an adapter pattern.

47. What are relational databases and non-relational databases

Relational databases are databases that use tables to organize and store data. They use a relational model to describe relationships between data, storing and representing data through rows and columns in tables. Relational databases use Structured Query Language (SQL) for data manipulation and querying.

Non-relational databases do not use the relational model or SQL. They use different data models and query languages to store and manipulate data. Common non-relational databases include document databases, key-value databases, column-store databases, etc. Non-relational databases are generally more suitable for storing and processing large amounts of unstructured data, offering higher scalability and flexibility.

48. What storage methods does Session have, what are the differences between them, and how to configure them

Session has the following storage methods:

Server memory: Stores Session data in the server's memory. This method has fast access speed but consumes server memory resources.
Database: Stores Session data in a database. This method enables Session persistence but increases database access overhead.
External services (e.g., Redis): Stores Session data in an external cache service, such as Redis. This method enables distributed storage and sharing of Session, improving system scalability and performance.

Setting the Session storage method can be done through configuration files or code. In ASP.NET, you can configure the Session storage method and other properties via the <sessionState> element in Web.config. Set the mode attribute to specify the storage method (e.g., InProc, SQLServer, Redis, etc.) and set corresponding connection strings or other configuration information. Alternatively, you can set the Session storage method in code, such as using the SessionStateModule's SessionStateMode property.

49. Please briefly describe the function and implementation mechanism of ViewState

ViewState is a mechanism for saving the state information of page controls between postbacks in a web page. It can save property values, event states, and view state of page controls, allowing the page's state to be restored during postback.

The implementation mechanism of ViewState is to save the state information of page controls in a hidden field named __VIEWSTATE. During page postback, ASP.NET automatically parses the value of the hidden field and restores the state of page controls.

Functions of ViewState include:

Saving property values of page controls: ViewState can save property values such as text in text boxes, checked state of checkboxes, selected items in drop-down lists, etc.
Saving event states of page controls: ViewState can save event states such as button click events, checkbox selection events, etc.
Saving view state of page controls: ViewState can save the view state of page controls, i.e., the position and style of controls on the page.

Note that ViewState increases page size and network transmission overhead. When using ViewState, pay attention to controlling its size to avoid excessive data transfer and page load delays. You can control whether ViewState is enabled by setting the EnableViewState property, and control the ViewState mode (e.g., Enabled, Disabled, Inherit) via the ViewStateMode property.

50. What is row-to-column and column-to-row in databases

Row-to-column and column-to-row are data transformation operations in databases.

Row-to-column (Row to Column) is the operation of converting row data in a database into column data. Normally, data in a database is stored as rows, with each row representing a record and each column representing a field. However, in some cases, it may be necessary to convert row data into column data for easier data analysis and querying. This can be achieved using aggregate functions, PIVOT operations, or custom query statements.

Column-to-row (Column to Row) is the operation of converting column data in a database into row data. Opposite to row-to-column, it converts column data into row data according to certain rules. This can be achieved using UNPIVOT operations or custom query statements.

51. What is the relationship between ADO.NET and ORM

ADO.NET (ActiveX Data Objects .NET) and ORM (Object-Relational Mapping) are two technologies for accessing databases, with a certain relationship in terms of database access layers.

ADO.NET is a set of classes and methods in the .NET framework for accessing databases. It provides a way to interact with databases based on connections, commands, and data readers. ADO.NET implements connection to databases, execution of SQL statements, and processing of results through a series of classes (such as SqlConnection, SqlCommand, SqlDataReader, etc.).

ORM is a technology for mapping object models to relational databases. It can map tables and records in a database to objects and properties, allowing developers to operate on databases using an object-oriented approach. ORM frameworks automatically handle the conversion between objects and databases, simplifying the development of the data access layer.

The relationship between ADO.NET and ORM is that ADO.NET is a low-level database access technology, while ORM provides a higher level of abstraction and encapsulation on top of ADO.NET. ORM frameworks can use ADO.NET as the underlying database access technology, mapping the relationship between objects and databases to achieve object persistence and simplified database operations.

Using an ORM framework can transform database operations into object operations, allowing developers to focus more on business logic implementation without worrying about lower-level database access details. ORM frameworks can provide higher development efficiency and code maintainability, as well as additional features like caching, lazy loading, etc. However, it should be noted that ORM frameworks are not suitable for all projects and scenarios; for some complex database operations, ADO.NET's low-level functionality may still be needed.

Summary

This article lists .NET interview questions provided by netizens and reference answers for each question, hoping to help you prepare for interviews. Some of the above questions are a bit old, which also reflects that the company's technology is relatively old. Due to different interview scenarios and question directions, you can answer accordingly based on the situation. The answers are for reference only. To excel in interviews, you need to continuously improve your basic knowledge and stay updated on the latest technology trends.

If you have different insights on the interview questions in this article, you can leave a comment below or submit a PR:

dotnet9/Assets.Dotnet9: Dotnet9 website's article repository (github.com)