MVC:

https://medium.com/dot-net-tutorial/top-50-asp-net-mvc-interview-questions-with-answers-1fd9b1638c61

SOLID Principle:

Bundling and Minification

Bundling and minification techniques were introduced in MVC 4 to improve request load time

Bundling

Bundling allows us to load the bunch of static files from the server into one HTTP request

Minification

Minification technique optimizes script or CSS file size by removing unnecessary white space and comments and shortening variable names to one character.

What is Keep and Peek?

keep(): marks the specified key in the dictionary for retention.

peek(): returns an object that contains the element that is

associated with the specified key, without marking the key for

deletion.

 Web Services

https://www.javatpoint.com/web-services-interview-questions

Rest Services

https://www.interviewbit.com/rest-api-interview-questions/

Rest

Rest is an architectural style that enables developers to build lightweight secure transactional web services which are used to modify the web resources accessed through URI.

Rest Principles:

REST defines 6 architectural constraints which make any web service – a true RESTful API.

·       Uniform interface

·       Client–server

·       Stateless

·       Cacheable

·       Layered system

·       Code on demand (optional)

Rest Features:

Rest uses appropriate HTTP Verbs

·       PUT

·       POST

·       GET

·       DELETE

·       PATCH

Rest uses hypermedia to handle the heterogenous client server communication.

Hypermedia: HATEOAS – Hypermedia as the engine of Application state

In the response, we can embed the link to the next resource.

1.     SOAP Vs REST

SOAP	REST
SOAP - Simple Object Access Protocol	REST - Representational State Transfer
SOAP is a protocol used to implement web services.	REST is an architectural design pattern for developing web services
SOAP cannot use REST as it is a protocol.	REST architecture can have SOAP protocol as part of the implementation.
SOAP specifies standards that are meant to be followed strictly.	REST defines standards but they need not be strictly followed.
SOAP client is more tightly coupled to the server which is similar to desktop applications having strict contracts.	The REST client is more flexible like a browser and does not depend on how the server is developed unless it follows the protocols required for establishing communication.
SOAP supports only XML transmission between the client and the server.	REST supports data of multiple formats like XML, JSON, MIME, Text, etc.
SOAP reads are not cacheable.	REST read requests can be cached.
SOAP uses service interfaces for exposing the resource logic.	REST uses URI to expose the resource logic.
SOAP is slower.	REST is faster.
Since SOAP is a protocol, it defines its own security measures.	REST only inherits the security measures based on what protocol it uses for the implementation.
SOAP is not commonly preferred, but they are used in cases which require stateful data transfer and more reliability.	REST is commonly preferred by developers these days as it provides more scalability and maintainability.

 

2.     While creating URI for web services, what are the best practices that needs to be followed?

Below is the list of best practices that need to be considered with designing URI for web services:

 

·       While defining resources, use plural nouns. Example: To identify user resource, use the name “users” for that resource.

·       While using the long name for resources, use underscore or hyphen. Avoid using spaces between words. For example, to define authorized users resource, the name can be “authorized_users” or “authorized-users”.

·       The URI is case-insensitive, but as part of best practice, it is recommended to use lower case only.

·       While developing URI, the backward compatibility must be maintained once it gets published. When the URI is updated, the older URI must be redirected to the new one using the HTTP status code 300.

·       Use appropriate HTTP methods like GET, PUT, DELETE, PATCH, etc. It is not needed or recommended to use these method names in the URI. Example: To get user details of a particular ID, use /users/{id} instead of /getUser

·       Use the technique of forward slashing to indicate the hierarchy between the resources and the collections. Example: To get the address of the user of a particular id, we can use: /users/{id}/address

 

3.     What are the best practices to develop RESTful web services?

 

·       Since REST supports multiple data formats, it is however good practice to develop REST APIs that accept and responds with JSON data format whenever possible. This is because a majority of the client and server technologies have inbuilt support to read and parse JSON objects with ease, thereby making JSON the standard object notation.

 

·       While naming the resource endpoints, ensure to use plural nouns and not verbs.

·       To represent the hierarchy of resources, use the nesting in the naming convention of the endpoints.

/authors/:id/address'

·       Error Handling should be done gracefully by returning appropriate error codes the application has encountered. HTTP Status codes that can be sent along with the response based on the scenario.

o   400 - Bad Request – client-side error - failed input validation.

o   401 - Unauthorized – The user is not authenticated and hence does not have authority to access the resource.

o   403 - Forbidden – User is authenticated but is not authorized to access the resource.

o   404 - Not Found – The resource is not found.

o   500 - Internal server error – This is a very generic server-side error that is thrown when the server goes down. This shouldn’t be returned by the programmer explicitly.

o   502 - Bad Gateway – Server did not receive a valid response from the upstream server.

o   503 - Service Unavailable – Some unexpected things happened

 

·       While retrieving huge resource data, it is advisable to include filtering and pagination of the resources. This is because returning huge data all at once can slow down the system and reduce the application performance

·       Good security practices are a must while developing REST APIs. The client-server communication must be private due to the nature of data sensitivity.

·       Since REST supports the feature of caching, we can use this feature to cache the data in order to improve the application performance.

·       Versioning needs to be done in case we are planning to make any changes with the existing endpoints. We do not want to break communication between our application and the apps that consume our application while we are working on the API release.

 

4.      What are Idempotent methods? How is it relevant in RESTful web services domain?

 

The meaning of idempotent is that even after calling a single request multiple times, the outcome of the request should be the same. While designing REST APIs, we need to keep in mind to develop idempotent APIs. This is because the consumers can write client-side code which can result in duplicate requests intentionally or not. Hence, fault-tolerant APIs need to be designed so that they do not result in erroneous responses.

 

5.     Can you tell what constitutes the core components of HTTP Request?

 

In REST, any HTTP Request has 5 main components, they are:

 

·       Method/Verb − This part tells what methods the request operation represents. Methods like GET, PUT, POST, DELETE, etc are some examples.

·       URI − This part is used for uniquely identifying the resources on the server.

·       HTTP Version − This part indicates what version of HTTP protocol you are using. An example can be HTTP v1.1.

·       Request Header − This part has the details of the request metadata such as client type, the content format supported, message format, cache settings, etc.

·       Request Body − This part represents the actual message content to be sent to the server.

 

6.     What constitutes the core components of HTTP Response?

 

·       Response Status Code − This represents the server response status code for the requested resource. Example- 400 represents a client-side error, 200 represents a successful response.

·       HTTP Version − Indicates the HTTP protocol version.

·       Response Header − This part has the metadata of the response message. Data can describe what is the content length, content type, response date, what is server type, etc.

·       Response Body − This part contains what is the actual resource/message returned from the server.

 

7.     PUT Vs POST

PUT	POST
PUT methods are used to request the server to store the enclosed entity in request. In case, the request does not exist, then new resource has to be created. If the resource exists, then the resource should get updated.	POST method is used to request the server to store the enclosed entity in the request as a new resource.
The URI should have a resource identifier. Example: PUT /users/{user-id}	The POST URI should indicate the collection of the resource. Example: POST /users
PUT methods are idempotent.	POST methods are not idempotent.
PUT is used when the client wants to modify a single resource that is part of the collection. If a part of the resource has to be updated, then PATCH needs to be used.	POST methods are used to add a new resource to the collection.
The responses are not cached here despite the idempotency.	Responses are not cacheable unless the response explicitly specifies Cache-Control fields in the header.
In general, PUT is used for UPDATE operations.	POST is used for CREATE operations.

 

8.     What makes REST services to be easily scalable?

 

REST services follow the concept of statelessness which essentially means no storing of any data across the requests on the server. This makes it easier to scale horizontally because the servers need not communicate much with each other while serving requests.

 

9.     Web Socket Vs Rest

REST	Web Socket
REST follows stateless architecture, meaning it won’t store any session-based data.	Web Socket APIs follow the stateful protocol as it necessitates session-based data storage.
The mode of communication is uni-directional. At a time, only the server or the client will communicate.	The communication is bi-directional, communication can be done by both client or server at a time.
REST is based on the Request-Response Model.	Web Socket follows the full-duplex model.
Every request will have sections like header, title, body, URL, etc.	Web sockets do not have any overhead and hence suited for real-time communication.
For every HTTP request, a new TCP connection is set up.	There will be only one TCP connection and then the client and server can start communicating.
REST web services support both vertical and horizontal scaling.	Web socket-based services only support vertical scaling.
REST depends on HTTP methods to get the response.	Web Sockets depend on the IP address and port number of the system to get a response.
Communication is slower here.	Message transmission happens very faster than REST API.
Memory/Buffers are not needed to store data here.	Memory is required to store data.

 

 

10.  What is a Resource in REST?

 

Any single item on the web can be considered as a resource like files, web pages and databases etc

 

11.  What is statelessness in RESTful Webservices?

 

The communication between client and server must be stateless. This means that each request from a service consumer should contain all the necessary information for the service to understand the meaning of the request, and all session state data should then be returned to the service consumer at the end of each request

12.  What are the advantages and disadvantages of statelessness in RESTful Webservices?

 

Advantages:

·       Web services can treat each method request independently.

·       Web services need not to maintain client’s previous interactions. It simplifies application design.

·       As HTTP is itself a statelessness protocol, RESTful Web services work seamlessly with HTTP protocol

Disadvantages:

·       Web services need to get extra information in each request and then interpret to get the client’s state in case client interactions are to be taken care of.

 

13.  What should be the purpose of OPTIONS and HEAD method of RESTful web services?

 

OPTIONS : list down the supported operations in a web service and should be read only.

HEAD : return only HTTP Header, no Body and should be read only.

 

14.  Can we implement transport layer security (TLS) in REST?

 

Yes, we can. TLS does the task of encrypting the communication between the REST client and the server and provides the means to authenticate the server to the client. It is used for secure communication as it is the successor of the Secure Socket Layer (SSL). HTTPS works well with both TLS and SSL thereby making it effective while implementing RESTful web services. One point to mention here is, the REST inherits the property of the protocol it implements. So security measures are dependent on the protocol REST implements.

 

15.  What is Payload in terms of RESTful web services?

 

Payload refers to the data passes in the request body. It is not the same as the request parameters. The payload can be sent only in POST methods as part of the request body.

 

16.  Is it possible to send payload in the GET and DELETE methods?

 

No, the payload is not the same as the request parameters. Hence, it is not possible to send payload data in these methods.

 

17.  How can you test RESTful Web Services?

 

RESTful web services can be tested using various tools like Postman, Swagger, etc

 

18.  What is the maximum payload size that can be sent in POST methods?

Theoretically, there is no restriction on the size of the payload that can be sent. But one must remember that the greater the size of the payload, the larger would be the bandwidth consumption and time taken to process the request that can impact the server performance.

 

 

 

 

 

Entity Framework:

https://www.javatpoint.com/entity-framework-interview-questions

1.         What is DBContext?

DbContext is an important class in Entity Framework API. It is a bridge between your domain or entity classes and the database. The primary class that is responsible for interacting with data as objects

2.         Entity Framework Architecture

The following figure shows the overall architecture of the Entity Framework.

 

Let's look at the components of the architecture individually.

·       EDM (Entity Data Model): EDM consists of three main parts - Conceptual model, Mapping and Storage model.

·       Conceptual Model: The conceptual model contains the model classes and their relationships. This will be independent from your database table design.

·       Storage Model: The storage model is the database design model which includes tables, views, stored procedures, and their relationships and keys.

·       Mapping: Mapping consists of information about how the conceptual model is mapped to the storage model.

·       LINQ to Entities: LINQ-to-Entities (L2E) is a query language used to write queries against the object model. It returns entities, which are defined in the conceptual model.

·       Entity SQL: Entity SQL is another query language (For EF 6 only) just like LINQ to Entities. However, it is a little more difficult than L2E and the developer will have to learn it separately.

·       Object Service: Object service is a main entry point for accessing data from the database and returning it back. Object service is responsible for materialization, which is the process of converting data returned from an entity client data provider (next layer) to an entity object structure.

·       Entity Client Data Provider: The main responsibility of this layer is to convert LINQ-to-Entities or Entity SQL queries into a SQL query which is understood by the underlying database. It communicates with the ADO.Net data provider which in turn sends or retrieves data from the database.

ADO.Net Data Provider: This layer communicates with the database using standard ADO.Net.

3.  ObjectContext

ObjectContext is a class that manages all the database operations, like database connection, and manages various entities of the Entity Model. We can say that ObjectContext is the primary class for accessing or working together with entities that are defined in the conceptual model.

ObjectContext is responsible for:

•                 Database connection

•                 It provides builtin Add, Update and Delete functions

•                 Object Set of every entity

•                 Provide State of pending changes

•                 It holds the changes done in entities

ObjectContext also encapsulates a few of things; they are:

•                 Connection to the Data Store or Database

•                 Metadata in the Entity Data Model (EDM)

•                 ObjectStateManager to track changes to the objects

 

4. ObjectContext Vs DbContext

 

s.no	Object Context	DBContext
1.	ObjectContext class is part of the core Entity Framework API, that allows us to perform queries, change and track updates of the Database by using strongly typed entity classes.	The DbContext class can be described as a wrapper of ObjectContext. It exposes the most commonly used features of ObjectContext.
	ObjectContext supports Compiled Queries.	DbContext does not support Compiled Queries.
	ObjectContext supports self-tracking of Entities	DbContext does not support self-tracking of Entities.
	ObjectContext is only useful in Model First and Database First approaches	DbContext is useful in Model First, Database First approach as well as Code First approach.
	ObjectContext can be used by Entity Framework 4.0 and below.	DBContext can be used by Entity Framework 4.1 and above.
	The ObjectContext class is not thread-safe.	Any public static (C#) or Shared (Visual Basic) members of DbContext are thread-safe. Any instance members are not guaranteed to be thread safe.

 

5. What is DbSet?

Ans. DbSet is a typed entity set which is used to perform create, read, update, and delete operations on a particular entity. DbSet is can only be created from a DbContext instance. DbSet does not support the Entity SQL methods.

6. What is ObjectSet?

Ans. ObjectSet a typed entity set which is used to perform create, read, update, and delete operations on a particular entity. ObjectSet is can only be created from an ObjectContext instance. ObjectSet does not support the Entity SQL methods.

7. How to execute plain SQL in EF6?

Ans. EF6 allows us to execute raw SQL queries to query the database. The following methods are used to execute raw SQL queries:

•                 DbSet.SqlQuery()

•                 DbContext.Database.SqlQuery()

•                 DbContext.Database.ExecuteSqlCommand()

8. Explain EagerLoading, Lazy Loading and Explicit Loading

•                 Lazy Loading: It is a process to delay the loading of related objects until it is required.

•                 Eager Loading: It occurs when you query for an object and all of the related objects are also returned. In eager loading, related objects are loaded automatically with its parent object

•                 Explicit Loading: Explicitly loading takes place when you have disabled Lazy loading, and you still want to lazy loading. For this, we have to call the load method on the related entities.

9. How can we handle concurrency in Entity Framework?

In EF, concurrency issue is resolved by using optimistic locking. To implement optimistic locking, right click on the EDMX designer and set the concurrency mode to Fixed. Now whenever we have concurrency issues you should get an OptimisticConcurrencyException error.

10. Explain different approaches in Entity Framework?

Code First:

In Code First Approach, we create the business domain classes first and then generate the database from it.

Model First:

In the Model-First approach, you create the entities, relationships, and inheritance hierarchies directly on the design surface of EDMX and then generate the database from your model.

Database First:

In Database First, We create the Model classes from the existing database.

11. Advantages and Disadvantages of Database first approach?

Advantages:

•                 Easy to create entity models if there is an existing database.

•                 Preferred approach for data intensive applications.

Disadvantages:

•                 Once we create a edmx file from an existing database, huge pile of code is generated.

•                 If we want to add the additional functionality to the models generated, we need to extend the models.

12. What are the advantages of Model First Approach?

•                 Model first approach gives the flexibility to design the Entity Models independently and gives an option to improve at later stages.

•                 Model classes can be created by drawing it in the edmx designer, so no much of database is required.

13. Advantages and disadvantages of Code First Approach?

Advantages:

•                 Based on business objects we can decide the database structure.

•                 We can decide which classes need to be serialized and can specify the collection to eager load.

•                 Good for smaller applications.

Disadvantages:

•                 All database related stuffs should be included in the code.

•                 For Stored Procs, we need to use the Fluent APIs to write it in code.

•                 Not good for data intensive applications.

14. Explain Optimistic Locking

Optimistic Locking is a strategy where you read a record, take note of a version number (other methods to do this involve dates, timestamps or checksums/hashes) and check that the version hasn't changed before you write the record back. When you write the record back you filter the update on the version to make sure it's atomic. (i.e. hasn't been updated between when you check the version and write the record to the disk) and update the version in one hit.

If the record is dirty (i.e. different version to yours) you abort the transaction and the user can re-start it.

This strategy is most applicable to high-volume systems and three-tier architectures where you do not necessarily maintain a connection to the database for your session. In this situation the client cannot actually maintain database locks as the connections are taken from a pool and you may not be using the same connection from one access to the next.

 

15. How Do You Truncate A Table Using Entity Data Model?

Unfortunately Entity Framework doesn’t include anything straight forward to handle this. But we can still call a T-SQL statement using entity framework that will still minimizes the developers work. We can call ExecuteStoreCommand() methond on ObjectContext as shown below.

Code:

using (var context = new MyTestDbEntities()){

    context.ExecuteStoreCommand("TRUNCATE table Dummy");

}

16. How Do You Query In Entity Model When The Result Has A Join From From Different Database Other Than The Entity Model?

 SELECT t1.c1, t2.c2 FROM table1 AS t1 JOIN table2 t2 ON t1.c1 = t2.c1

As the entity model doesn’t support querying from any entity other than the entities defined in Entity Data Model, we have to query aginst the data base using ExecuteStoredQuery of the context.

Following code snippet shows how to query when other databases are joined.

Code:

string query = "SELECT t1.c1, t2.c2 FROM table1 AS t1 JOIN table2 t2 ON t1.c1 = t2.c1";

using (var context = new SampleEntities())

{

  ObjectResult records = context.ExecuteStoreQuery(query);

  foreach (DbDataRecord record in records)

  {      }

 

}