Paths

A path expression (or simply a path) represents a set of values that are reachable when traversing a given sequence of links or properties from some source set.

The result of a path expression is:

1. if a path does not end with a property reference, then it represents a unique set of objects reachable from the set at the root of the path;

2. if a path does end with a property reference, then it represents a list of property values for every element in the unique set of objects reachable from the set at the root of the path.

The syntactic form of a path is:

expression path-step [ path-step ... ]

where path-step is:
  step-direction pointer-name

The individual path components are:

expression

Any valid expression.

step-direction

It can be one of the following:

• . for an outgoing or “forward” link reference

• .< for an incoming or “backward” link reference

• @ for a link property reference

pointer-name

This must be a valid link or link property name.

Consider the following schema:

type User {
    required property name -> str;
    multi link friends -> User {
        property since -> cal::local_date;
    }
}

abstract type Owned {
    required link owner -> User;
}

type Issue extending Owned {
    required property title -> str;
}

The example below shows a path that represents the names of all friends of all User objects in the database.

SELECT User.friends.name;

And this represents all sources of the owner links that have a User as target:

SELECT User.<owner;

By default backward links don’t infer any type information beyond the fact that it’s an Object. To ensure that this path specifically reaches Issue a type intersection operator must be used:

SELECT User.<owner[IS Issue];

The following represents a set of all dates on which users became friends, if since is defined as a link property on the User.friends link:

SELECT User.friends@since;