Nestjs , How to get entity table name?

When working with TypeORM in NestJS, you might need to retrieve the table name associated with an entity in the database under certain circumstances. This can be accomplished in various ways, primarily by leveraging TypeORM's API and decorators. Below is one method to retrieve the table name of a TypeORM entity:

1. Using Entity Metadata Explorer:

TypeORM provides a robust API for exploring the metadata of all entities managed by the entity manager. Through this metadata, you can access details such as the table name corresponding to the entity. Here is an example of how to use this API:

typescript
import { Injectable } from '@nestjs/common';
import { InjectEntityManager } from '@nestjs/typeorm';
import { EntityManager } from 'typeorm';

@Injectable()
export class YourService {
    constructor(@InjectEntityManager() private entityManager: EntityManager) {}

    getTableName(entity: Function): string {
        // Retrieve the entity's metadata
        const metadata = this.entityManager.getMetadata(entity);
        // Return the table name
        return metadata.tableName;
    }
}

In this example, the YourService class includes a method getTableName that accepts an entity class as a parameter. It uses the EntityManager's getMetadata method to fetch the entity's metadata, from which you can access the tableName property storing the corresponding database table name.

1. Using Decorators and Reflection:

If you prefer a method that doesn't rely directly on the TypeORM EntityManager, you can utilize TypeScript's decorators and reflection API. This approach requires defining the table name information via a custom decorator when the entity is declared, and then retrieving this information using reflection when needed.

typescript
import 'reflect-metadata';

// Custom decorator to define and reflect the table name
function Table(name: string): ClassDecorator {
    return (target) => {
        Reflect.defineMetadata('tableName', name, target);
    };
}

@Table('your_table_name')
export class YourEntity {}

// In the service, read the table name
@Injectable()
export class YourService {
    getTableName(entity: Function): string {
        return Reflect.getMetadata('tableName', entity);
    }
}

Both methods are applicable in NestJS applications for retrieving the table name of a TypeORM entity. The choice between them depends on your specific requirements and preferences.

When using TypeORM with NestJS, to retrieve the table name of an entity, you can utilize the getMetadata() method of TypeORM. This method can be invoked on the DataSource or EntityManager to obtain metadata about registered entities. Here is an example of retrieving the entity's table name:

First, ensure that your NestJS project has set up TypeORM and created entities. For example, we have an entity named User:

typescript
@Entity('users')
export class User {
  // Entity properties...
}

In this entity, we use the @Entity decorator to specify that this entity will be mapped to the database table named 'users'.

To retrieve the table name of this entity, you can inject the DataSource and use it to access the entity's metadata. Here is a possible service class method to achieve this:

typescript
import { Injectable } from '@nestjs/common';
import { DataSource } from 'typeorm';
import { User } from './user.entity';

@Injectable()
export class UserService {
  constructor(private dataSource: DataSource) {}

  getTableName() {
    const userRepository = this.dataSource.getRepository(User);
    const metadata = userRepository.metadata;
    return metadata.tableName; // This will return 'users'
  }
}

In the code above, we:

1. Inject the DataSource.
2. Use dataSource.getRepository(User) to obtain the repository for the User entity.
3. Access the metadata property of the repository to retrieve the tableName.

This allows us to obtain the table name mapped to the entity. This method is highly useful in various scenarios, such as when building generic features where knowing the specific table name is required.