Entity in TypeORM is a class that represents a database table or a group of linked data. It determines the structure and relationships of the data that will be kept in the database. The creation of objects (rows) that will be kept in the database is outlined by an entity.

The use of entities in TypeORM is intended to simplify type-safe, object-oriented database interaction for developers. Entity definition allows TypeORM to produce the required SQL queries and control database and application communication. As a result, manual SQL coding is no longer required, and it is simpler to manage the database schema over time.

Entities in TypeORM can be decorated with additional metadata to indicate the sort of data they represent, how they should be stored to the database, and how they can be searched. They can also have properties and relationships with other entities. Developers may interact with databases in a comfortable and natural way with the aid of TypeORM, free from having to worry about the nitty-gritty of database communication.

Properties and Relationships in Entity

In TypeORM, entities are classes that represent tables or collections of data in a database. An entity class defines the structure and relationships of the data that will be stored in the database.

Properties: An entity class has properties that correspond to columns in the database table. Each property represents a piece of data that will be stored in the database. Properties can be decorated with metadata to specify the data type, whether it's required or optional, and other constraints.

Entity Relationships: Entities can have relationships with other entities, such as one-to-one, one-to-many, or many-to-many relationships. These relationships represent how the data in the entities is related to each other. For example, a one-to-one relationship between two entities means that each entity instance is associated with a single instance of the other entity.

Entity Decorators: TypeORM provides several decorators that can be used to decorate entity properties and relationships. Some of the most commonly used entity decorators are:

• @Column: Used to decorate a property and specify its data type and other constraints.

• @PrimaryGeneratedColumn: Used to decorate a property and specify that it should be automatically generated by the database (such as an auto-incrementing primary key).e.g id

• @OneToOne: Used to decorate a relationship and specify a one-to-one relationship between two entities.

• @OneToMany: Used to decorate a relationship and specify a one-to-many relationship between two entities.

• @ManyToMany: Used to decorate a relationship and specify a many-to-many relationship between two entities.

By understanding entities in TypeORM, developers can work with databases in a more efficient and intuitive way, without having to write raw SQL statements. With the help of TypeORM, they can create entities that represent the structure and relationships of the data they want to store and then use those entities to interact with the database in a type-safe and object-oriented manner.

Creating and using Entity

Creating an Entity in TypeORM:

1. Setting up the Project: To create an entity in TypeORM, you need to have a project setup with TypeORM installed. You can use npm or yarn to install TypeORM in your project.

2. Creating the Entity Class: Once the project is set up, you can create a new entity class. An entity class is a normal TypeScript class that has properties that correspond to columns in the database table. The properties can be decorated with metadata to specify the data type and other constraints.

3. Mapping the Entity to the Database: To map the entity class to the database, you need to use the @Entity decorator from TypeORM. This decorator is used to specify that the class is an entity and the name of the database table that it corresponds to.

4. Creating Entity Instances: After the entity is mapped to the database, you can create instances of the entity class to represent rows in the database table.

Using Entities in TypeORM:

1. Saving Entity Instances: To save an entity instance to the database, you can use the Entity Manager's save method. This method will persist the entity instance to the database and automatically generate the necessary SQL statements.

2. Querying Entity Data: To retrieve data from the database, you can use the Entity Manager's find method. This method allows you to query the database and retrieve entity instances that match certain criteria. You can also use advanced queries to retrieve data based on relationships between entities.

3. Updating Entity Instances: To update an entity instance, you can modify its properties and then save the instance back to the database using the Entity Manager's save method. TypeORM will automatically generate the necessary SQL statements to update the database.

4. Deleting Entity Instances: To delete an entity instance, you can use the Entity Manager's remove method. This method will delete the entity instance from the database and automatically generate the necessary SQL statements.

In conclusion, entities in TypeORM provide a powerful and convenient way to work with databases. By defining entities as classes that represent the structure and relationships of the data you want to store, you can interact with the database in a type-safe and object-oriented manner. With the help of the Entity Manager, you can save, retrieve, update, and delete data from the database with ease, without having to write raw SQL statements.

The benefits of using entities in TypeORM include:

1. Type-Safety: Entities in TypeORM provide type-safety, meaning that you can work with databases in a way that ensures that your data is always of the correct type.

2. Object-Oriented Approach: Entities in TypeORM allow you to work with databases in an object-oriented way, meaning that you can define entities as classes and use instances of those classes to represent rows in the database.

3. Abstraction from SQL: TypeORM provides a high level of abstraction from SQL, meaning that you don't have to write raw SQL statements to interact with the database.

4. Improved Productivity: By using entities in TypeORM, you can improve your productivity by working with databases in a more efficient and intuitive way.

5. Strong Entity Relationships: TypeORM supports strong entity relationships, meaning that you can define relationships between entities and retrieve data based on those relationships.

In summary, entities in TypeORM provide a powerful and convenient way to work with databases, allowing you to improve your productivity and work with databases in a type-safe and object-oriented manner. Whether you're working on a small project or a large enterprise application, TypeORM's entities can help you to achieve your goals more efficiently and effectively.