TypeOrm-Postgres-NestJs @Column('decimal') is returning string

Question

I have some columns with type decimal. I am using query builder for aggregation. The only problem is after aggregating the result the fields that have decimal values are returning as string after executing the query.

I want to set it globally across my project to consider decimal numbers in entity as decimal numbers only while executing queries and not string.

I have tried using transformer with @Column() but it is not working.

  @Column('decimal', {
    transformer: {
      to(value) {
        return value;
      },
      from(value) {
        return parseFloat(value);
      },
    },
  })
  price: number;

but even if it works I don't want to write same thing for all columns. I want to make this setting globally.

Answer 1

This is known safeguard in postgresql, because aggregate operations can result in values that can fall outside the range of number type in JavaScript. Hence as a safety, these values are returned as string.

A similar safeguard exists in mysql as well (which can be handled using supportBigNumbers: false setting in node-mysql package).

You can create a NestJS transformer (like below) and then reuse it in your entities. You can adjust the precision and scale to suite your needs.

// transformer
export class DecimalColumnTransformer {
    to(data: number): number {
        return data;
    }
    from(data: string): number {
        return parseFloat(data);
    }
}

// entity
@Column('decimal', {
    precision: 5,
    scale: 2,
    transformer: new DecimalColumnTransformer(),
})
price: number;