Entity Framework Core is a modern, open-source object-relational mapper (ORM) that enables .NET developers to work with relational databases using .NET objects. It eliminates the need for most of the data-access code that developers usually need to write.
In this article, we’ll explore some of the most common Entity Framework Core interview questions and example answers to help you prepare for your next .NET job interview.
5 Common Entity Framework Core Interview Questions
Here are 5 common Entity Framework Core interview questions that hiring managers may ask and how to best answer them:
Question: Explain the benefits of using Entity Framework Core.
Example Answer: Some key benefits of using Entity Framework Core include:
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Simplifies data access – EF Core handles the low-level data access code, allowing developers to work with data in terms of .NET objects and queries instead of SQL. This can boost productivity.
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Database provider independence – EF Core can connect to SQL Server, SQLite, MySQL, PostgreSQL and more. The data access code can stay the same even if the database is changed.
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Automatic change tracking – EF Core tracks changes made to entities synchronizing object changes back to the database. This removes a lot of repetitive CRUD code.
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Migrations – EF Core provides a migration system to incrementally update the database schema without dropping the database. This helps with version control of the data model.
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LINQ support – EF Core allows composing LINQ queries against the database to load and manipulate data efficiently without SQL. LINQ queries get converted to SQL behind the scenes.
Question: Describe the scenarios in which you may use Entity Framework Core.
Example Answer: Some cases where Entity Framework Core works very well include:
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Rapid prototyping – EF Core makes it easy to start working with data quickly without having to hand-code data access. This helps with rapid prototyping and iteration.
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O/RM for new projects – For new projects where no data access layer exists yet, EF Core provides a modern O/RM to interface with the database using .NET objects.
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Reducing data access code – In existing projects with a lot of repetitive data access code, EF Core can eliminate that boilerplate code.
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Microservices – The lightweight nature of EF Core makes it well-suited for microservices architectures and container-based deployment where a full-featured ORM may be too heavy.
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Multi-database applications – EF Core provides database abstraction allowing the same application code to target different database backends like MySQL or PostgreSQL.
Question: Define the main components of Entity Framework Core.
Example Answer: The main components of Entity Framework Core include:
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DbContext – The main class that coordinates Entity Framework functionality. It handles querying, change tracking, logging, caching, and more.
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DbSet – Represents a collection of entities in the database. DbContext has a property for each DbSet entity.
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Entity – A class that maps to a database table. Contains properties for each column. EF Core allows you to use POCO classes as entities.
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Connection string – Defines the database connection info like server name, database name, user ID and password. Set on DbContext.
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Model – Contains the entity mappings. Can be created from your entities or from an existing database (database first).
Question: What are the three different parts of the Entity model?
Example Answer: The three parts of an Entity Framework model are:
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Conceptual model – Describes the entities, relationships, and structure of the application’s domain model.
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Storage model – Describes the database schema – tables, columns, keys, etc.
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Mapping – Bridges the conceptual model and storage model by mapping entities to database tables.
The conceptual model represents the application domain while the storage model represents the database structure. The mapping layer maps everything together.
Question: Describe the two types of migration in Entity Framework Core.
Example Answer: Entity Framework Core supports two types of migration for incrementally updating the database schema:
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Code First Migrations – Migrations are defined in C# code. Each migration class incrementally updates the schema. Applying migrations runs the Up() method.
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Automatic Migrations – The migration steps are automatically scaffoldled based on changes to the model. The developer doesn’t write explicit migration code.
Code first migrations provide more control but require writing migration code. Automatic migrations are easier to use but provide less control over how schema changes are applied.
Entity Framework Core Concepts
Here are some additional common Entity Framework Core interview questions that test your knowledge of key concepts and features:
Question: What is the difference between DbContext and ObjectContext in EF Core?
Answer: DbContext is the newer main context class used in EF Core. ObjectContext is the equivalent context class used in older EF6 and EF4. The main differences are:
- DbContext has a simpler API surface making it easier to use
- DbContext can be created with dependency injection unlike ObjectContext
- DbContext uses DbSet while ObjectContext uses ObjectSet collections
- DbContext is lighter weight and has better performance
Overall, DbContext has a more modern, streamlined approach compared to ObjectContext.
Question: How does Entity Framework Core handle concurrency conflicts?
Answer: EF Core detects concurrency conflicts by tracking each entity’s original values when it is queried from the database. Before saving changes, it checks whether any of an entity’s property values were modified externally since being queried.
If the current values don’t match the original values, meaning something changed the row externally, a DbUpdateConcurrencyException is thrown indicating a concurrency violation. The application must decide how to resolve the conflict.
Question: Explain the difference between database first, model first and code first approaches.
Answer:
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Database first – An EF model is reverse engineered from an existing database schema. Useful for working with legacy databases.
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Model first – An EF model is created using a visual designer to define entities and relationships. Code is then generated from the model.
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Code first – EF model and mapping code is hand written first. The database schema is created from the model code. Useful for greenfield development.
The database and model first approaches are database driven while code first is code driven. Code first offers the most control and flexibility.
Question: What is the Unit of Work pattern and how does EF Core implement it?
Answer: The Unit of Work pattern groups operations into a single transaction so that all changes succeed or fail together.
EF Core implements Unit of Work automatically – all changes made between calls to SaveChanges() are wrapped in a transaction, so if one operation fails none of the changes are applied. SaveChanges() commits the transaction.
Question: How does Entity Framework Core handle object caching?
Answer: EF Core keeps a change tracker cache containing queried entities and monitors them for changes. This first-level cache sits between the application and the database.
EF Core doesn’t cache actual data but tracks entities as they are read from the database and modified in the app. This avoids needing to hit the database multiple times for unchanged data.
The change tracker cache is discarded after SaveChanges().
Question: What are some strategies to improve performance with EF Core?
Answer: Some optimization strategies include:
- Use NoTracking queries in read-heavy workloads to skip change tracking
- Use AsNoTracking for entities that don’t need tracking
- Explicitly load related data instead of relying on lazy loading
- Use projection to just select needed columns/properties
- Add appropriate indexes to the database based on query filters
- Batch save changes instead of calling SaveChanges frequently
Caching and compiling queries can also boost performance.
Entity Framework Code Examples
The interview may also include a coding exercise to test your hands-on Entity Framework Core skills. Here are some examples of tasks you may be asked to demonstrate:
Question: Show an example of configuring DbContext and performing database operations.
// ApplicationDbContext inherits from DbContextpublic class ApplicationDbContext : DbContext { public DbSet<Customer> Customers { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { optionsBuilder.UseSqlServer(@"Server=.SQLEXPRESS;Database=CustomerDB;Trusted_Connection=True;"); }}// Save a new customerusing (var context = new ApplicationDbContext()){ context.Add(new Customer()); context.SaveChanges(); }This shows setting up DbContext, adding a new entity, and saving changes.
Question: Write a LINQ query to retrieve customers by country.
using (var context = new ApplicationDbContext()){ var UKCustomers = context.Customers .Where(c => c.Country == "UK") .ToList(); }This filters customers by country into a new list using LINQ.
Question: Show implementing and applying a manual database migration.
public class InitialMigration : Migration{ protected override void Up(MigrationBuilder migrationBuilder) { migrationBuilder.CreateTable( name: "Customers", columns: table => newEntity Framework Interview Preparation: An Overview
ADO. If you want to query the database in an object-oriented way, you can use the open-source ORM framework NET Entity Framework. It works with. NET-based applications and internally wraps ADO. NET. This article contains Best Entity Framework Interview Questions & Answers.
Prepare yourself for the interview with the help of the ADO.NET Core interview question answer the PDF file and get a suitable development position on the cloud-based application including web application, IoT application, and Mobile application. So, If you want to win in Azure DevOps interview. Go through these Azure DevOps Interview Questions and Answers once.
Entity Framework Interview Questions & Answers
- What is ADO. NET Entity Framework?ADO. The NET Entity Framework is an ORM framework that lets developers work with different relational databases, such as SQL Server, Oracle, DB2, MYSQL, and more. It lets programmers work with data as entities or objects. Using the Entity Framework, developers issue queries using LINQ, then retrieve and manipulate data as strongly typed objects using C# or VB. NET Framework.
- What other O/RMs you can use with . NET-based applications? The following O/RMs, you can use with . NET-based applications: Entity Framework 6. x Entity Framework Core Dapper N Hibernate .
- What are Micro O/RMs? A Micro ORM is designed so that you can focus on working with database tables instead of making changes to the database schema, keeping track of changes, and other tasks that are less important. EF 6. x and EF Core are both O/RMs because they have all the features you could want.
- Which is what Dapper is? Dapper is a simple or micro ORM for the NET world. The StackOverflow team made Dapper to solve their problems and made it open source. Its a NuGet library that can be added to any . NET project for database operations.
- What is an SQL injection attack? Hackers use SQL injection attacks to get private data from a company’s database. The application layer (also called “front-end”) attack takes advantage of bad programming in our apps, which lets hackers add SQL commands to your code that uses SQL statements. SQL Injection happens because the fields that users can enter let SQL statements go through and directly query the database. SQL Injection issue is a common issue with an ADO. NET Data Services query.
- How to protect against SQL injection attacks in Entity Framework? Entity Framework is safe from injection attacks because it always creates parameterized SQL commands. These commands help protect our database against SQL Injection. It is possible to do an SQL injection attack in Entity SQL syntax by giving bad data that is used in a query and in parameter names. This should never happen, so you should never mix user input with Entity SQL command text.
- How do different approaches to domain modeling in Entity Framework work? There are three ways to use Entity Framework: Database-first: Entity Framework writes the code if we start with a database. 2. Model-first: Entity Framework makes both the database and the code if we start with a visual model. 3. Code-first: Entity Framework makes the database if we start with code.
- What are POCO classes? The word “POCO” doesn’t mean that your classes are boring or old. The term “POCO” only means that the POCO classes don’t have any references that are unique to the entity framework or NET framework. Plain Old CLR Object (POCO) entities are domain objects that are already in your app and that you use with Entity Framework.
- What is a proxy object? A proxy object is an object that is made from a POCO class or entities generated by the Entity Framework to help track changes and load data slowly. When making a proxy class object, you need to follow some rules. The class must be public and not sealed. Each property must be marked as virtual. Each property must have a public getter and setter. Any collection navigation properties must be typed as ICollection .
- EF has a set of enums called “EntityStates” that define the different states that an entity can be in at any given time. These states are: Added; Modified; Deleted; Unchanged; Detached; and many more.
- What are the different types of inheritance in Entity Framework? Inheritance in the Entity Framework is similar to inheritance for classes in C#. In Entity Framework, you can connect an inheritance tree to one or more database tables, depending on your needs. EF lets you inherit in three different ways: table-per-hierarchy (TPH), table-per-type (TPT), and table-per-concrete-type (TPC).
- What are the different ways to design a model in Code First? In the Entity Framework Code First method, our POCO classes are mapped to database objects using a set of rules that Entity Framework defines. When you define your POCO classes, you don’t have to follow these rules. If you want to change how the rules work, you can use the fluent API or data annotations to set up and map your POCO classes to database tables. Defining the model in EF Code First can be done in two different ways:
- What C# Datatype is mapped with which Datatype in SQL Server? The following table has the list of C# Datatype mapping to the corresponding SQL Server Datatype: C# Data TypeindexOf() intint stringnvarchar(Max) decimaldecimal(18,2) floatreal byte[]varbinary(Max) datetimedatetime boolbit bytetinyint shortsmallint longbigint doublefloat charNo mapping sbyteNo mapping objectNo mapping .
- What is Code First Migrations in Entity Framework? The code-first approach lets you use POCOs to define model classes that meet the needs of the domain. So, you have full control over the classes that are being written or implemented. Using the Package Manager Console in Visual Studio, Code First Migrations lets you use your model classes to create a new database or make changes to an existing one.
- There is a table called “Migrations History” in EF6 that stores information about changes that were made to a database. It is part of the application database and is used by Code First Migrations. When you do the first migration on the database, this table is made. In this table, information about the schema versions of one or more EF Code First models in a database is kept. When you use Microsoft SQL Server, this table was a system table in EF 5. When you use Microsoft SQL Server, this table was a system table in EF 5.
- How does automatic migration work? IEntity Framework supports automatic migration, which means you don’t have to manually move model changes. So, the EF will take care of the application when you run it.
- Why would you want to use a typed entity set? A typed entity set lets you create, read, update, and delete an entity. DbSet can only be created from a DbContext instance. DbSet does not support the Entity SQL methods.
- What is an ObjectSet? An ObjectSet is a typed entity set that lets you create, read, update, and delete an entity. ObjectSet is can only be created from an ObjectContext instance. ObjectSet does not support the Entity SQL methods.
- How do I run plain SQL in EF6? We can run raw SQL queries to query the database in EF6. To run raw SQL queries, you can use the following methods: DbSet SqlQuery() DbContext. Database. SqlQuery() DbContext. Database. ExecuteSqlCommand() .
- How does EF support Transaction? When you use SaveChanges() to add, change, or delete data in the database, EF adds that operation to a transaction. So, you don’t need to open a transaction scope explicitly. Q21. Some of the things that Entity Framework can do are querying, modeling, saving, change tracking, concurrency, caching, transactions, configuration, built-in conventions, and migrations. These are the features of Entity Framework. Q22. For what reason is the conceptual model used? The conceptual model is also known as the Conceptual Data Definition Language Layer or C-Space. It contains the entities/model classes and also their relationships. This all thing doesnt affect our database table design. Because it makes sure that XML files clearly show business objects and relationships Q23. What is the mapping model used for? The mapping model is also known as the C-S Space or the Mapping Schema Definition Language layer. It has details on how the conceptual model is linked to the storage model. This model connects the conceptual layer’s business objects and their connections to the logical layer’s tables and connections. Q24. What is the storage model used for? The storage model is also known as the S-Space or Store Space Definition Language Layer. This model always stands for the storage area in the backend. Because of this, it’s also known as the database design model, which is made up of stored procedures, keys, views, tables, and relationships between them. Q25. What exactly does “migration” mean in Entity Framework? Entity Framework added the “migration tool” to keep the database schema up to date automatically. Entity Framework offers two types of migration: code-based migration and automated migration. Q26. What does the . what does an edmx file contain? When you use EDMX files, Classes can be automatically created so they can work with the application. The conceptual models, storage models, and mappings are all stored in the EDMX file. It has all the information you need about SQL objects and tables. The crucial information needed to render models graphically with ADO. NET is also contained. Its 3 types are MSL, CSDL, and SSDL. Q27. Mention some XML generation methods that the dataset object provides. To make XML, Dataset objects offer the following methods:1 With GetXml(), you can get a string that contains an XML document. 2. When you call ReadXml(), an XML file is read into a Dataset object. 3. Write XML (): This method saves the XML data to a file. Q28. Why is the T4 entity important in Entity Framework? T4 files are very important for making Entity Framework code. To read the EDMX XML files, T4 code templates are used. The C# behind the code is then generated by the T4 files. Just entity and the context classes are contained in the generated C# behind the code. Q29. What does Entity Framework’s navigation property mean? It stands for a foreign key relationship in the database of Entity Framework. With this property type, you can describe the connections between the things in a database. When you use object-oriented programming, you define the relationships so that they make sense. Q30. What does “deferred execution” mean in Entity Framework? It means that we can delay the evaluation of any expression until we want its real value to show up. So, we can greatly improve performance by not running any unnecessary code. Queries are put off until the query object or query variable goes through a loop. Q31. What does “database concurrency” mean? It means that multiple people can access and change the same data in the same database at the same time. Concurrency controls keep the consistencyof data protected in such situations. Q32. What is the best way to handle database concurrency? Optimist locking can be used to handle database concurrency. To lock something, right-click on the EDMX designer and choose “Fixed” as the concurrency model. If there is a concurrency problem, a positive concurrency exception error shows up. Q33. Explain SSDL, CSDL, and MSL divisions in an EDMX file. 1. SSDL stands for Storage Schema Definition Language. Mapping to RDBMS data structure is defined in this division.
- 2. CSDL stands for Conceptual Schema Definition Language. It is an app that exposes conceptual abstraction. The model objects description can be obtained in this division. 3. MSL stands for Mapping Schema Language. MSL connects CSDL and SSDL. It’s also possible to say that it connects the model to the storage. Q34. Explain the terms dbset and dbcontext.
- 1. Any entity set in a dbset class can have dbset-operations added to, changed, read, or deleted. The dbset type properties that map to the database tables and views need to be added to the context class (from dbcontext).
- 2. dbcontext- It is an important class in Entity Framework API. This links a domain class or entity to the database. Its main responsibility is to communicate with the database. Q35. How do I use an Object Set in Entity Framework? An object set is a type of entity set that can be used to read, update, create, and delete any existing entity. An Object Context instance is the only way to make it. It does not support any kind of Entity SQL method. Q36. In depth, describe eager loading, lazy loading, and explicit loading. 1. As soon as the object query is sent, all of its related objects are also sent back. Along with the parent object, all objects that are related to it are automatically loaded. If you use the Include method in EF 6, you can get eager loading. 2. This type of loading only happens when we want lazy loading to happen. For processing explicit loading, the right load method should be called directly. The load method can be used to get explicit loading in EF 6. 3. Lazy loading means that the process of loading related objects is put off until we need them. Only objects you need are returned in the lazy loading. At the same time, the other objects that are related are only returned when we need them. Q37. What do singularizing and pluralizing do in the Entity Framework? In Entity Framework, one of the most important jobs of singularizing and pluralizing is giving objects meaningful names. This feature can be processed through the . edmx file. When this feature is used, the coding rules for the singular and plural will be applied. If there are two or more records in an object, the convention names have an extra s after them. Q38. How do I use micro ORMs in Entity Framework? The micro ORM isn’t designed to make database schemas, keep track of changes, change database schemas, etc. Instead, working with database tables is what it does best. Entity Framework Core and Entity Framework 6 are called O/RMs because they have all of the functions and features that you could want. Q40. As you read a record, you should write down a version number, timestamp, date, or hash. This is called optimistic locking. After that, you can write the code back and make sure the record hasn’t changed. As we write the record back, we check the update against the version to make sure it’s atomic. Then the version is updated in a single hit. Q41. How does EF support transactions? When we use Save Changes in Entity Framework to add, change, or delete data in the database, that process is wrapped in a transaction. Q42. Which namespace is used for the inclusion of the . NET data provider for the SQL server in your . NET code?We use namespace as – System. Data. SqlClient for the inclusion of a . NET data provider for SQL server in our . NET code. Q43. When should different modeling entry points be used? The Code First method works best when we already have the domain classes. The Database First method, on the other hand, works best when we have a database. There is also the Model First method, which is used when there are no database or model classes. Q44. Mention the primary functions of the Entity Framework. EF lets domain classes be linked to the database schema. EFAlterations in the entities are kept on track. EF enables the execution of LINQ queries to SQL. The changes to stats in EF are saved in the database. Q45. What are the benefits of the Model First Approach? The Model First Approach lets you design the Entity Models separately and gives you ways to make them better later on. This method doesn’t need a lot of databases because we can use the EDMX designer to draw model classes and make them. Q46. Which approach do you think is the best in Entity Framework? There isn’t a single approach that can be called the best in Entity Framework. The approaches are mostly chosen based on the needs and types of the projects. The Database First approach should be used if there is already a database. In this case, the model-first approach is the best choice since there is no database and the model classes. The Code-First method is the best choice if the domain classes are available. Q47. LINQ to Entities is one of the most popular query languages in Entity Framework. What does it mean to you? It mostly helps you write queries against objects to get entities based on how the conceptual models are defined. Q48. What do you know about Entity SQL? It’s a different query language for entities that’s like LINQ. However, it is complicated than LINQ to Entities. If programmers want to use this language, they will need to learn it on their own. Q49. How would you use Entity Framework to handle a lot of data? There are different ways that Entity Framework can handle a lot of data. One way is to use the As NoTracking method, which stops Entity Framework from keeping track of changes to entities. This saves memory and speeds up the program. For more complicated queries or operations, the second plan is to use stored procedures instead of LINQ queries because they run faster. Q50. When it comes to Entity Framework, what do you know about ComplexType? ComplexType is a property of entity types that is not a scale This type helps users to assign scalar relationships between entities.
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