Interview

20 Dapper Interview Questions and Answers

Prepare for the types of questions you are likely to be asked when interviewing for a position where Dapper will be used.

Dapper is a popular object-relational mapper (ORM) for the .NET framework. It is known for its high performance and low learning curve. When applying for a position that uses Dapper, you can expect to be asked questions about your experience and understanding of the ORM. In this article, we will review some of the most commonly asked Dapper questions and provide suggested responses.

Dapper Interview Questions and Answers

Here are 20 commonly asked Dapper interview questions and answers to prepare you for your interview:

1. What is Dapper?

Dapper is a micro-ORM (object-relational mapper) for .NET. It provides a simple way to map objects to database tables and execute SQL queries.

2. What are the advantages of using Dapper in a project?

Dapper is a micro-ORM (object-relational mapper) which is designed to provide fast and simple data access for .NET applications. It is lightweight and easy to use, and it can greatly improve the performance of a .NET application by eliminating the need to write boilerplate code to access data.

3. Which classes provided by the .NET framework does Dapper use to communicate with databases?

Dapper uses the SqlConnection and SqlCommand classes in the .NET framework to communicate with databases.

4. Can you explain how Dapper works?

Dapper is a micro-ORM (object-relational mapper) for .NET. It provides a simple way to map objects to database tables and execute SQL queries. It is fast and lightweight, and does not require a lot of configuration.

5. Does Dapper support lazy-loading and caching features? If yes, then how do you implement them?

Dapper does support lazy-loading features, but it does not have built-in caching features. In order to implement lazy-loading with Dapper, you will need to use a separate library such as the LazyCache library.

6. How can you get multiple result sets from a single database call when using Dapper?

Dapper allows you to get multiple result sets from a single database call by using the QueryMultiple method. This method returns a MultiResult object, which can be used to access the individual result sets.

7. Can you explain what Multi Mapping is?

Multi Mapping is the process of mapping multiple rows from a single database table to multiple objects. This is often necessary when working with relational data, as each row in a table may represent a different object. Dapper makes this process easy by allowing developers to specify which columns from the table should be mapped to which properties on the object.

8. Is it possible to dynamically map a POCO class to a table name when using Dapper? If yes, then how do we go about doing this?

Yes, it is possible to dynamically map a POCO class to a table name when using Dapper. We can do this by using the SqlMapper.GetTypeMap method. This method allows us to specify the POCO class that we want to map to a table, as well as the table name that we want to map it to.

9. What are the different ways that Dapper supports for mapping stored procedures or functions to an entity?

Dapper supports three different ways of mapping stored procedures or functions to an entity. The first way is to use the default mapping, which will map the stored procedure or function to the entity based on the naming conventions used. The second way is to use the explicit mapping, which allows you to specify the stored procedure or function that should be used for each entity. The third way is to use the dynamic mapping, which will map the stored procedure or function to the entity based on the input and output parameters of the stored procedure or function.

10. What’s your understanding of the term “Dapper Contrib”?

Dapper Contrib is an open source project that adds a number of helper methods to the Dapper micro-ORM. These helper methods make it easier to work with Dapper, and can provide a significant performance boost over using the standard Dapper methods.

11. How can you implement CRUD operations on a repository without writing SQL queries when using Dapper?

Dapper provides a number of methods that can be used to perform CRUD operations on a repository without writing SQL queries. These methods include Execute, Query, and QueryFirstOrDefault.

12. Why do you think Dapper has more stars than Entity Framework on GitHub?

I think that Dapper has more stars than Entity Framework on GitHub because it is a simpler library that is easier to use. Entity Framework is a more full-featured library, but that can also make it more complicated and harder to use.

13. What is QueryMultiple() in context of Dapper? When would you recommend its usage?

QueryMultiple is a method in Dapper that allows you to execute multiple queries against a database in a single call. This can be useful if you need to perform multiple operations against a database as part of a single transaction. For example, you might use QueryMultiple to insert a new record into a database table and then retrieve the newly generated ID for that record in a single call.

14. Can you give me some examples where you have used Dapper to achieve significant performance improvements in data access speeds over other similar frameworks like ADO.NET or NHibernate?

Dapper has been used in a number of high-performance data access scenarios, including:

– retrieving data from a large number of records in a database table (e.g. millions of records)
– retrieving data from a database that is under high load
– retrieving data from a database that is located in a remote location

Dapper has also been used in scenarios where the data being accessed is complex in nature, such as when retrieving data from an XML document or from a JSON object.

15. Can you explain what dynamic parameters are? When should they be used?

Dynamic parameters are a type of object that can be used in place of traditional parameters when making a database call. They are useful when you do not know the number or types of parameters that will be needed ahead of time. For example, if you were building a search function that allowed users to specify any number of filters, you could use a dynamic parameter to pass in all of the filters as a single object.

16. What are some best practices for improving the performance of Dapper applications?

Some best practices for improving the performance of Dapper applications include using async methods wherever possible, using compiled queries, and avoiding dynamic type mapping. Additionally, batching SQL statements can also help improve performance.

17. Can you tell me which extension methods exist for the IDbConnection interface?

The IDbConnection interface has a number of extension methods available for working with data. These methods include Execute, Query, and ExecuteScalar.

18. Can you give me some examples where you have implemented complex object-relational mappings in a Dapper application?

I have implemented complex object-relational mappings in a Dapper application in a few different ways. One way is to use the built-in Dapper methods to map objects to relational data. Another way is to use a custom mapper to map objects to relational data. Finally, I have also used a combination of both methods to achieve the desired results.

19. Can you explain why Dapper uses DynamicParameters instead of SqlParameterCollection?

Dapper uses DynamicParameters instead of SqlParameterCollection because it is more efficient and easier to use. With DynamicParameters, you can simply add parameters to your SQL query without having to create a separate SqlParameterCollection. This makes it easier to write and maintain your code, and it also makes your code more efficient.

20. Are there any disadvantages of using Dapper?

While Dapper is incredibly fast and easy to use, it does have some disadvantages. One is that it is not as feature-rich as some other ORMs, so it may not be the best choice for more complex applications. Additionally, because it is not as widely used as some other ORMs, there can be a learning curve in getting started with it.

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