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Lesson 4.2: Inserting polymorphic data

Inferring types

In the previous lesson, we saw how we could use match clauses in Insert queries in order to have new data reference existing data. In this lesson, we’ll see how we can use that strategy to perform polymorphic inserts. We have already created a new promotion entity for the Spring Sale with this query from a previous exercise.

insert
$spring-sale isa promotion,
    has code "SPR24",
    has name "Spring Sale 2024",
    has start-timestamp 2024-03-15T00:00:00,
    has end-timestamp 2024-03-31T23:59:59;

studio fail Do not run

However, we have not yet assigned any books to this sale. This sale is a pretty big one, so we’re going to assign every book in the store to it with a 10% discount.

match
$spring-sale isa promotion, has code "SPR24";
$book isa book;
insert
(promotion: $spring-sale, item: $book) isa promotion-inclusion,
    has discount 0.10;

studio runstudio check Run and commit

By matching books using the supertype book, this query will add all books to the promotion, regardless of whether they are paperbacks, hardbacks, or ebooks. In this case, TypeDB is using type inference to resolve the inheritance polymorphism in the write query. We can just as easily use interface or parametric polymorphism in data writes!

Exercise

Write three new Insert queries. The first should create a new promotion with the following details:

  • The code "SFF24".

  • The name "Sci-Fi & Fantasy Festival 2024".

  • The start date (inclusive) 19th April 2024.

  • The end date (exclusive) 27th April 2024.

The second should match any book with a genre attribute with the value "science fiction" and add it to the promotion with a 15% discount. The third should match any book with the genre "fantasy" and add it with a 20% discount.

Sample solution 
insert
$sff-festival isa promotion,
    has code "SFF24",
    has name "Sci-Fi & Fantasy Festival 2024",
    has start-timestamp 2024-04-19T00:00:00,
    has end-timestamp 2024-04-26T23:59:59;

studio run Run

match
$sff-festival isa promotion, has code "SFF24";
$book isa book, has genre "science fiction";
insert
(promotion: $sff-festival, item: $book) isa promotion-inclusion,
    has discount 0.15;

studio run Run

match
$sff-festival isa promotion, has code "SFF24";
$book isa book, has genre "fantasy";
insert
(promotion: $sff-festival, item: $book) isa promotion-inclusion,
    has discount 0.20;

studio runstudio check Run and commit

Inferring roles

In addition to inferring types of referenced data, TypeDB is able to infer the roles of roleplayers when inserting new relations. This allows us to write significantly more concise Insert queries. For example, in the following query, we insert rating and action-execution relations without specifying roles!

match
$user-13 isa user, has id "u0013";
$frankenstein isa book, has isbn-13 "9780486282114";
insert
$review isa review, has id "r0034",
    has score 8;
($review, $frankenstein) isa rating;
($review, $user-13) isa action-execution,
    has timestamp 2024-03-19T03:32:00.073;

studio runstudio check Run and commit

For this query, TypeDB is able to infer that $review plays the review role and $frankenstein plays the rated role in rating. This is because:

  • rating has roles rating:review and rating:rated.

  • $review is of type review.

  • review plays rating:review but not rating:rated.

  • $frankenstein is of type book.

  • book plays rating:rated but not rating:review.

These constraints mean that TypeDB can infer the roles of $review and $frankenstein unambiguously, as they could not play any other roles. The same applies to the action-execution relation. Conversely, if one or more of the roleplayers can play multiple roles, then TypeDB is unable to infer them and throws an exception. Consider the following query, for instance.

match
$us isa country, has name "United States";
$ma isa state, has name "Massachusetts";
insert
($us, $ma) isa locating;

studio run Try running

The types country and state can play both location:location and location:located, so any of the following four combinations of roles would be valid:

  • (location: $us, located: $ga) isa locating;

  • (located: $us, location: $ga) isa locating;

  • (location: $us, location: $ga) isa locating;

  • (located: $us, located: $ga) isa locating;

It is obvious to us that the first statement is the correct one, but TypeDB cannot determine this unambiguously, so we would have to specify the roles when inserting this particular locating relation.

Exercise

Frankenstein is often considered to be one of the earliest works of science fiction, but is instead listed under the "horror" genre in the bookstore database. As a result, it wasn’t added to the Sci-Fi & Fantasy Festival promotion by our previous query. Insert a new relation to explicitly add it to the promotion with a 15% discount, and use role inference to avoid specifying any necessary roles.

Sample solution 
match
$sff-festival isa promotion, has code "SFF24";
$frankenstein isa book, has isbn-13 "9780486282114";
insert
($sff-festival, $frankenstein) isa promotion-inclusion,
    has discount 0.15;

studio runstudio check Run and commit