How to Use SQL Databases in a NestJS Application With TypeORM
An Object-Relational Mapper (ORM) is a library that implements the Object-Relational mapping technique. This lets you write SQL database queries using the object-oriented paradigm of your preferred language.
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NestJS provides high-level support for TypeORM out-of-the-box. The dedicated TypeORM package makes integration relatively easy.
Step 1: Installing Dependencies
Before using TypeORM in a NestJS application, you must install it with its native NestJS package and your preferred SQL database. SQLite is a simple, install-free option.
Run the following command to install TypeORM and its native NestJS package, usingthe npm package manager:
Run the following command to install SQLite:
Step 2: Creating an Entity
An entity is a collection of fields defining the data stored in a database. TypeORM uses the entity file to create a table in your database.
Follow the steps below to create an entity:
For example:
The entity file above creates this table in your database:
PRIMARY KEY AUTO_INCREMENT
property_1
varchar(255)
property_2
property_3
TheTypeORM documentationcovers entities in further detail.
Step 3: Connecting Your Application to a Database
Now that your entity is set up, you’ll need to connect your application to a database. This example uses SQLite.
Follow the steps below to connect your application to a database:
Step 4: Creating a Repository
A repository is an entity’s access layer used to make queries (insert, delete, save, find, etc.) on a table created by the entity in the database. TypeORM supports the repository design pattern, thus, each entity has its own repository.
TypeORM automatically creates a repository for your entity when you follow the steps below:
Step 5: Injecting Your Repository to Its Service Using Dependency Injection
Dependency injection is a software engineering technique that is a form of the inversion of control principle. It shifts the burden of dependency management from client code to the library or service it depends upon.
Follow the steps below to inject your repository into a service:
Now that your setup is complete, it’s possible to makeSQL querieson it to retrieve or modify data.
Making SQL Queries with TypeORM
You can make any simple SQL query by calling TypeORM’s repository methods on therepovariable inside your service class. You can also create complex SQL queries by using TypeORM’s query builder.
Want to learn more about SQL? Having a handle on the various SQL query commands is a great way to get ahead.
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