20 TypeORM Interview Questions and Answers

TypeORM is an Object Relational Mapper (ORM) for Node.js and TypeScript. It is a powerful tool that helps developers to easily connect to databases and manipulate data. If you are applying for a position that requires knowledge of TypeORM, it is important to be prepared for questions about this tool. In this article, we will review some common TypeORM interview questions and provide guidance on how to answer them.

TypeORM Interview Questions and Answers

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

1. What is TypeORM?

TypeORM is an Object Relational Mapper (ORM) for TypeScript and JavaScript. It allows you to work with your data in a more object-oriented fashion, making it easier to work with databases in a more abstract way.

2. Can you explain how to use TypeORM in a Node.js server application?

TypeORM is a Node.js ORM that can be used with TypeScript and JavaScript. It is a powerful tool that provides a way to manage databases in a Node.js application. To use TypeORM, you first need to install it in your project. You can do this with the following command:

npm install typeorm –save

Once TypeORM is installed, you can use it in your Node.js server application by importing the library and creating a connection to your database. TypeORM provides a variety of ways to interact with your database, including creating models, running queries, and more.

3. What are the main features of TypeORM?

TypeORM is an ORM that can run in NodeJS, Browser, Cordova, PhoneGap, Ionic, React Native, NativeScript, Expo, and Electron platforms and can be used with TypeScript and JavaScript (ES5, ES6, ES7, ES8). It supports both Active Record and Data Mapper patterns, unlike most other ORM frameworks that only support one of the two. It also has an extremely active and helpful community.

4. How do you migrate from one version to another of your database schema with TypeORM?

To migrate from one version to another of your database schema with TypeORM, you will need to use the TypeORM CLI. This tool will allow you to automatically generate migration files based on the changes you have made to your entities. Once you have generated these migration files, you can then run them to update your database schema.

5. What are some advantages of using TypeORM over other ORMs like Sequelize or Mongoose?

TypeORM is a newer ORM that has gained popularity due to its robust feature set and ease of use. Some of the advantages of using TypeORM include its support for multiple databases (including MySQL, PostgreSQL, and MongoDB), its ability to automatically generate database schemas, and its support for Promises and async/await.

6. What libraries can be used for writing unit tests in Typescript?

There are many libraries that can be used for writing unit tests in Typescript. Some popular ones include Jest, Mocha, and Chai.

7. Is it possible to write custom decorators with TypeORM? If yes, then how?

Yes, it is possible to write custom decorators with TypeORM. This can be done by creating a custom decorator function and then applying that function to the desired entity class.

8. What does the @Entity() annotation do when applied to a class?

The @Entity() annotation marks a class as a TypeORM entity, which means it will be stored in a database. The annotation can also be used to specify options for the entity, such as the name of the table that should be used to store it.

9. Can you explain what an abstract entity is and why would someone want to use it?

An abstract entity is an entity that is not mapped to a database table. This can be useful if you want to create a base class that other entities can inherit from. By making an entity abstract, you can prevent it from being instantiated on its own.

10. Why should you avoid calling methods on Entities directly?

When you call methods on Entities directly, you bypass the EntityManager and its ability to track changes to your Entities. This means that any changes you make to your Entities will not be persisted to the database unless you explicitly call EntityManager#persist(…) or EntityManager#flush().

11. Can you give me examples of the different types of relations that can be defined between entities using TypeORM?

There are three types of relations that can be defined between entities using TypeORM: one-to-one, one-to-many, and many-to-many. A one-to-one relation means that each entity is related to only one other entity. A one-to-many relation means that each entity is related to multiple other entities. A many-to-many relation means that each entity is related to multiple other entities, and those other entities are also related to multiple other entities.

12. What’s the difference between a primary and secondary key in TypeORM?

A primary key is a column that is used to uniquely identify a row in a table. A secondary key is a column that is used to provide an additional way to identify a row in a table.

13. What are the different ways to define a query using TypeORM?

There are three different ways to define a query using TypeORM:

1) The first way is to use the find method. This method will return all entities that match the given criteria.

2) The second way is to use the findOne method. This method will return the first entity that matches the given criteria.

3) The third way is to use the query method. This method will allow you to write a custom SQL query.

14. What happens if a method’s input parameter doesn’t match its type definition?

If a method’s input parameter doesn’t match its type definition, TypeORM will throw an error.

15. What are some common pitfalls that people make when using TypeORM?

A common mistake that people make when using TypeORM is not specifying the data type for columns in their database tables. This can lead to problems when trying to insert or update data, as TypeORM will not know how to handle the data if it is not of the correct type. Another mistake is not properly configuring the relationship between entities, which can lead to errors when querying for data.

16. What is the best way to handle errors while running queries using TypeORM?

TypeORM provides a built-in error handler that can be used to handle errors that occur while running queries. This error handler will log the error and provide information about the query that caused the error.

17. What is the benefit of separating out the configuration settings from code in TypeORM?

By separating out the configuration settings from the code, it becomes much easier to manage and change those settings without having to wade through code. It also makes it easier to share configuration settings between different projects, or to have different settings for different environments.

18. What are the benefits of using TypeORM?

TypeORM is a great tool for working with relational databases in JavaScript. It has a wide range of features, including the ability to automatically generate database schema based on your data models, and support for various database types including MySQL, PostgreSQL, and SQLite. It also has a robust query builder that makes it easy to construct complex SQL queries.

19. What are the disadvantages of using TypeORM?

While TypeORM is a great tool, it does have some disadvantages. One is that it can be slow when used with large databases. Another is that it doesn’t support some features that other ORMs do, such as eager loading.

20. What are some alternatives to TypeORM?

Some alternatives to TypeORM are Sequelize, Doctrine, and Propel.