In TypeORM how do I have a pre-calculated field on an Entity based on other fields of that Entity?

Question

I want to make a 'rating' field on my User Entity. The User Entity has a relationship to the Rating Entity, on User there is a field called ratingsReceived, which is an eager load of all Ratings assigned to that User.

I want the 'rating' field on User to be a mean calculation of all rating values which is a field on Rating Entity called 'ratingValue'.

So essentially I want this calculation to be the value of every User 'rating' field:

ratingsReceived.reduce((acc, curr) => acc + curr.ratingValue, 0) / ratingsReceived.length

The fields in question are 'ratingsReceived' on User:

  @OneToMany(
    () => Rating,
    rating => rating.ratingTo
  )
  ratingsReceived: Rating[];

And 'ratingValue' on Rating:

  @Column('decimal')
  @Min(0)
  @Max(5)
  ratingValue: number;

Answer 1

After trial and error, managed to create a workaround for this like so:

// After load is called after the entity loads during find() and similar
// I placed this decorator on my User Entity
@AfterLoad()
  calculateRating = async () => {
    const result = await getRepository(Rating)
      .createQueryBuilder('ratings')
      .where('ratings."ratingToId" = :id', { id: this.id })
      .getRawAndEntities();

    const ratingsAboveZero = result?.entities?.filter(x => parseFloat(x.ratingValue));
    const count = ratingsAboveZero.length;

    if (count > 0) {
      this.rating =
        ratingsAboveZero.reduce((acc, curr) => {
          return acc + parseFloat(curr.ratingValue);
        }, 0) / count;

      this.ratingCount = count;
    } else {
      this.rating = 0;
      this.ratingCount = 0;
    }
  };