relationship
Relationships
Relationships in Red are defined by the is relationship trait. It should receive (at least) a Str named parameter called :model
that represents the related model, a Callable positional parameter that will return one (or more) referencing columns, and it must have a sigil. The sigil can be:
$- Represents abelongs torelationship that "stores" only 1 element. Red will run the callable passing the model itself as the only parameter.@- Represents ahas manyrelationship that "stores" aResultSeqof elements. Red will run the callable passing the model defined by the:modelnamed parameter.
(for the experimental has-one, please take a look at experimental doc)
So, for example:
# Person.rakumod
use Red:ver<2>;
model Person {
has UInt $!id is serial;
has Str $.name is column;
has @.books is relationship(*.author-id, :model<Book>);
}# Book.rakumod
use Red:ver<2>;
model Book {
has UInt $!id is serial;
has Str $.name is column;
has UInt $!author-id is referencing(*.id, :model<Person>);
has $.author is relationship(*.author-id, :model<Person>);
}Book has a foreign key (.author)
that's auto pre-fetched using a join based on book.author_id = person.id.
Person has no foreign key but it does have a relationship (@.books) that isn't pre-fetched because it's a has many relationship. So when its value is accessed
a new query is run.
On that example, to create a new book related to (written by) a given person, one could do something like:
my $author = Person.^all.first: *.name eq "Chico Buarque";
$author.books.create: :name<Benjamin>;As mentioned, @.books is a ResultSeq, so it accepts any of its methods, eg:
$author.books.grep(*.starts-with: "Ben").elemsFor getting the number of books written by "Chico Buarque" that starts with "Ben".