A path expression (or simply a path) represents a set of values that are reachable by traversing a given sequence of links or properties from some source set of objects.
Consider the following schema:
type User {
required property email -> str;
multi link friends -> User;
}
type BlogPost {
required property title -> str;
required link author -> User;
}The simplest path is simply User. This is a set reference that refers to all User objects in the database.
select User;Paths can traverse links. The path below refers to all Users who are the friend of another User.
select User.friends;Paths can traverse arbitrarily many links.
select BlogPost.author.friends.friends;Paths can terminate with a property reference.
select BlogPost.title; # all blog post titles
select BlogPost.author.email; # all author emails
select User.friends.email; # all friends' emailsAll examples thus far have traversed links in the forward direction, however
it’s also possible to traverse links backwards with .< notation. These
are called backlinks.
Starting from each user, the path below traverses all incoming links labeled
author and returns the union of their sources.
select User.<author;As written, EdgeDB infers the type of this expression to be
BaseObject, not BlogPost. Why? Because in theory, there may be
several links named author that point to User.
BaseObject is the root ancestor of all object types and it only contains
a single property, id.
Consider the following addition to the schema:
type User {
# as before
}
type BlogPost {
required link author -> User;
}
type Comment {
required link author -> User;
}With the above schema, the path User.<author would return a mixed set of
BlogPost and Comment objects. This may be desirable in some cases, but
commonly you’ll want to narrow the results to a particular type. To do so, use
the type intersection operator: [is Foo]:
select User.<author[is BlogPost]; # returns all blog posts
select User.<author[is Comment]; # returns all commentsPaths can also reference link properties
with @ notation. To demonstrate this, let’s add a property to the User.
friends link:
type User {
required property email -> str;
multi link friends -> User;
multi link friends -> User {
property since -> cal::local_date;
}
}The following represents a set of all dates on which friendships were formed.
select User.friends@since;For simplicity, all examples above use set references like User as the root
of the path; however, the root can be any expression returning object types.
Below, the root of the path is a subquery.
db> ... ... ...
with edgedb_lovers := (
select BlogPost filter .title ilike "EdgeDB is awesome"
)
select edgedb_lovers.author;This expression returns a set of all Users who have written a blog post
titled “EdgeDB is awesome”.
For a full syntax definition, see the Reference > Paths.
