Question

98

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

rated 0 times [ 101] [ 3] / answers: 1 / hits: 6211 / 4 Years ago, mon, march 30, 2020, 12:00:00

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;

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asalewisc

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answered 4 Years ago cristoferjordih · Accepted Answer

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;

    }

  };