The select
command retrieves or computes a set of values. We’ve already
seen simple queries that select primitive values.
db>
select 'hello world';
{'hello world'}
db>
select [1, 2, 3];
{[1, 2, 3]}
db>
select {1, 2, 3};
{1, 2, 3}
With the help of a with
block, we can add filters, ordering, and
pagination clauses.
db> ... ...
with x := {1, 2, 3, 4, 5}
select x
filter x >= 3;
{3, 4, 5}
db> ... ...
with x := {1, 2, 3, 4, 5}
select x
order by x desc;
{5, 4, 3, 2, 1}
db> ... ...
with x := {1, 2, 3, 4, 5}
select x
offset 1 limit 3;
{2, 3, 4}
These queries can also be rewritten to use inline aliases, like so:
db> ...
select x := {1, 2, 3, 4, 5}
filter x >= 3;
However most queries are selecting objects that live in the database. For demonstration purposes, the queries below assume the following schema.
module default {
abstract type Person {
required property name -> str { constraint exclusive };
}
type Hero extending Person {
property secret_identity -> str;
multi link villains := .<nemesis[is Villain];
}
type Villain extending Person {
link nemesis -> Hero;
}
type Movie {
required property title -> str { constraint exclusive };
required property release_year -> int64;
multi link characters -> Person;
}
}
Let’s start by selecting all Villains
objects in the database. In this
example, there are only three. Remember, Villain
is a reference to the set of all Villain objects.
db>
select Villain;
{ default::Villain {id: ea7bad4c...}, default::Villain {id: 6ddbb04a...}, default::Villain {id: b233ca98...}, }
For the sake of readability, the id
values have been truncated.
By default, this only returns the id
of each object. If serialized to JSON,
this result would look like this:
[
{"id": "ea7bad4c-35d6-11ec-9519-0361f8abd380"},
{"id": "6ddbb04a-3c23-11ec-b81f-7b7516f2a868"},
{"id": "b233ca98-3c23-11ec-b81f-6ba8c4f0084e"},
]
To specify which properties to select, we attach a shape to Hero
. A
shape can be attached to any object type expression in EdgeQL.
db>
select Villain { id, name };
{ default::Villain { id: ea7bad4c..., name: 'Whiplash' }, default::Villain { id: 6ddbb04a..., name: 'Green Goblin', }, default::Villain { id: b233ca98..., name: 'Doc Ock' }, }
Nested shapes can be used to fetch linked objects and their properties. Here we
fetch all Villain
objects and their nemeses.
db> ... ... ...
select Villain {
name,
nemesis: { name }
};
{ default::Villain { name: 'Green Goblin', nemesis: default::Hero {name: 'Spider-Man'}, }, ... }
In the context of EdgeQL, computed links like Hero.villains
are treated
identically to concrete/non-computed links like Villain.nemesis
.
db> ... ... ...
select Hero {
name,
villains: { name }
};
{ default::Hero { name: 'Spider-Man', villains: { default::Villain {name: 'Green Goblin'}, default::Villain {name: 'Doc Ock'}, }, }, ... }
To filter the set of selected objects, use a filter <expr>
clause. The
<expr>
that follows the filter
keyword can be any boolean expression.
To reference the name
property of the Villain
objects being selected,
we use Villain.name
.
db> ...
select Villain {id, name}
filter Villain.name = "Doc Ock";
{default::Villain {id: b233ca98..., name: 'Doc Ock'}}
This query contains two occurrences of Villain
. The first
(outer) is passed as the argument to select
and refers to the set of all
Villain
objects. However the inner occurrence is inside the scope of
the select
statement and refers to the object being
selected.
However, this looks a little clunky, so EdgeQL provides a shorthand: just drop
Villain
entirely and simply use .name
. Since we are selecting a set of
Villains, it’s clear from context that .name
must refer to a link/property
of the Villain
type. In other words, we are in the scope of the
Villain
type.
db> ...
select Villain {name}
filter .name = "Doc Ock";
{default::Villain {name: 'Doc Ock'}}
To filter by id
, remember to cast the desired ID to uuid:
db> ...
select Villain {id, name}
filter .id = <uuid>"b233ca98-3c23-11ec-b81f-6ba8c4f0084e";
{ default::Villain { id: 'b233ca98-3c23-11ec-b81f-6ba8c4f0084e', name: 'Doc Ock' } }
Filters can be added at every level of shape nesting. The query below applies a
filter to both the selected Hero
objects and their linked villains
.
db> ... ... ... ... ...
select Hero {
name,
villains: {
name
} filter .name ilike "%er"
} filter .name ilike "%man";
{ default::Hero { name: 'Iron Man', villains: {default::Villain {name: 'Justin Hammer'}}, }, default::Hero { name: 'Spider-Man', villains: { default::Villain {name: 'Shocker'}, default::Villain {name: 'Tinkerer'}, default::Villain {name: 'Kraven the Hunter'}, }, }, }
Note that the scope changes inside nested shapes. When we use .name
in
the outer filter
, it refers to the name of the hero. But when we use
.name
in the nested villains
shape, the scope has changed to
Villain
.
Order the result of a query with an order by
clause.
db> ...
select Villain { name }
order by .name;
{ default::Villain {name: 'Abomination'}, default::Villain {name: 'Doc Ock'}, default::Villain {name: 'Green Goblin'}, default::Villain {name: 'Justin Hammer'}, default::Villain {name: 'Kraven the Hunter'}, default::Villain {name: 'Loki'}, default::Villain {name: 'Shocker'}, default::Villain {name: 'The Vulture'}, default::Villain {name: 'Tinkerer'}, default::Villain {name: 'Zemo'}, }
The expression provided to order by
may be any singleton
expression, primitive or otherwise.
In EdgeDB all values are orderable. Objects are compared using their id
;
tuples and arrays are compared element-by-element from left to right. By
extension, the generic comparison operators =
,
<
, >
, etc. can be used with any two
expressions of the same type.
You can also order by multiple
expressions and specify the direction with an asc
(default) or desc
modifier.
When ordering by multiple expressions, arrays, or tuples, the leftmost expression/element is compared. If these elements are the same, the next element is used to “break the tie”, and so on. If all elements are the same, the order is not well defined.
db> ... ... ...
select Movie { title, release_year }
order by
.release_year desc then
str_trim(.title) desc;
{ default::Movie {title: 'Spider-Man: No Way Home', release_year: 2021}, ... default::Movie {title: 'Iron Man', release_year: 2008}, }
When ordering by multiple expressions, each expression is separated with the
then
keyword. For a full reference on ordering, including how empty values
are handled, see Reference > Commands > Select.
EdgeDB supports limit
and offset
clauses. These are
typically used in conjunction with order by
to maintain a consistent
ordering across pagination queries.
db> ... ... ...
select Villain { name }
order by .name
offset 3
limit 3;
{ default::Villain {name: 'Hela'}, default::Villain {name: 'Justin Hammer'}, default::Villain {name: 'Kraven the Hunter'}, }
The expressions passed to limit
and offset
can be any singleton
int64
expression. This query fetches all Villains except the last (sorted
by name).
db> ... ...
select Villain {name}
order by .name
limit count(Villain) - 1;
{ default::Villain {name: 'Abomination'}, default::Villain {name: 'Doc Ock'}, ... default::Villain {name: 'Winter Soldier'}, # no Zemo }
Shapes can contain computed fields. These are EdgeQL expressions that are
computed on the fly during the execution of the query. As with other clauses,
we can use leading dot notation (e.g. .name
) to
refer to the properties and links of the object type currently in scope.
db> ... ... ...
select Villain {
name,
name_upper := str_upper(.name)
};
{ default::Villain { id: 4114dd56..., name: 'Abomination', name_upper: 'ABOMINATION', }, ... }
As with nested filters, the current scope changes inside nested shapes.
db> ... ... ... ... ... ... ... ...
select Villain {
id,
name,
name_upper := str_upper(.name),
nemesis: {
secret_identity,
real_name_upper := str_upper(.secret_identity)
}
};
{ default::Villain { id: 6ddbb04a..., name: 'Green Goblin', name_upper: 'GREEN GOBLIN', nemesis: default::Hero { secret_identity: 'Peter Parker', real_name_upper: 'PETER PARKER', }, }, ... }
Fetching backlinks is a common use case for computed fields. To demonstrate this, let’s fetch a list of all movies starring a particular Hero.
db> ... ... ...
select Hero {
name,
movies := .<characters[is Movie] { title }
} filter .name = "Iron Man";
{ default::Hero { name: 'Iron Man', movies: { default::Movie {title: 'Iron Man'}, default::Movie {title: 'Iron Man 2'}, default::Movie {title: 'Iron Man 3'}, default::Movie {title: 'Captain America: Civil War'}, default::Movie {title: 'The Avengers'}, }, }, }
The computed backlink villains
is a combination of the backlink
operator
.<
and a type intersection [is Villain]
. For a full
reference on backlink syntax, see EdgeQL > Paths.
Instead of re-declaring backlinks inside every query where they’re needed, it’s common to add them directly into your schema as computed links.
abstract type Person {
required property name -> str {
constraint exclusive;
};
multi link movies := .<characters[is Movie]
}
In the example above, the Person.movies
is a multi link
. Including
these keywords is optional, since EdgeDB can infer this from the assigned
expression .<characters[is Movie]
. However, it’s a good practice to
include the explicit keywords to make the schema more readable and “sanity
check” the cardinality.
This simplifies future queries; Person.movies
can now be traversed in
shapes just like a non-computed link.
select Hero {
name,
movies: { title }
} filter .name = "Iron Man";
There’s no limit to the complexity of computed expressions. EdgeQL is designed to be fully composable; entire queries can be embedded inside each other. Below, we use a subquery to select all movies containing a villain’s nemesis.
db> ... ... ... ... ... ... ...
select Villain {
name,
nemesis_name := .nemesis.name,
movies_with_nemesis := (
select Movie { title }
filter Villain.nemesis in .characters
)
};
{ default::Villain { name: 'Loki', nemesis_name: 'Thor', movies_with_nemesis: { default::Movie {title: 'Thor'}, default::Movie {title: 'Thor: The Dark World'}, default::Movie {title: 'Thor: Ragnarok'}, default::Movie {title: 'The Avengers'}, }, }, ... }
All queries thus far have referenced concrete object types: Hero
and
Villain
. However, both of these types extend the abstract type Person
,
from which they inherit the name
property.
It’s possible to directly query all Person
objects; the resulting set with
be a mix of Hero
and Villain
objects (and possibly other subtypes of
Person
, should they be declared).
db>
select Person { name };
{ default::Villain {name: 'Abomination'}, default::Villain {name: 'Zemo'}, default::Hero {name: 'The Hulk'}, default::Hero {name: 'Iron Man'}, ... }
You may also encounter such “mixed sets” when querying a link that points to an
abstract type (such as Movie.characters
) or a union type
.
db> ... ... ... ... ... ...
select Movie {
title,
characters: {
name
}
}
filter .title = "Iron Man 2";
{ default::Movie { title: 'Iron Man 2', characters: { default::Villain {name: 'Whiplash'}, default::Villain {name: 'Justin Hammer'}, default::Hero {name: 'Iron Man'}, default::Hero {name: 'Black Widow'}, }, }, }
We can fetch different properties conditional on the subtype of each object
by prefixing property/link references with [is <type>]
. This is known as a
polymorphic query.
db> ... ... ... ... ... ... ...
select Person {
name,
secret_identity := [is Hero].secret_identity,
number_of_villains := count([is Hero].villains),
nemesis := [is Villain].nemesis {
name
}
};
{ default::Villain { name: 'Green Goblin', secret_identity: {}, number_of_villains: 0, nemesis: default::Hero {name: 'Spider-Man'}, }, default::Hero { name: 'Spider-Man', secret_identity: 'Peter Parker', number_of_villains: 6, nemesis: {}, }, ... }
This syntax might look familiar; it’s the type intersection again. In effect, this operator conditionally returns the value of the referenced field only if the object matches a particular type. If the match fails, an empty set is returned.
The line secret_identity := [is Hero].secret_identity
is a bit redundant,
since the computed property has the same name as the polymorphic field. In
these cases, EdgeQL supports a shorthand.
db> ... ... ... ... ... ...
select Person {
name,
[is Hero].secret_identity,
[is Villain].nemesis: {
name
}
};
{ default::Villain { name: 'Green Goblin', secret_identity: {}, nemesis: default::Hero {name: 'Spider-Man'}, }, default::Hero { name: 'Spider-Man', secret_identity: 'Peter Parker', nemesis: {}, }, ... }
Relatedly, it’s possible to filter polymorphic links by subtype. Below, we
exclusively fetch the Movie.characters
of type Hero
.
db> ... ... ... ... ...
select Movie {
title,
characters[is Hero]: {
secret_identity
},
};
{ default::Movie { title: 'Spider-Man: Homecoming', characters: {default::Hero {secret_identity: 'Peter Parker'}}, }, default::Movie { title: 'Iron Man', characters: {default::Hero {secret_identity: 'Tony Stark'}}, }, ... }
To select several values simultaneously, you can “bundle” them into a “free object”. Free objects are a set of key-value pairs that can contain any expression. Here, the term “free” is used to indicate that the object in question is not an instance of a particular object type; instead, it’s constructed ad hoc inside the query.
db> ... ... ... ... ...
select {
my_string := "This is a string",
my_number := 42,
several_numbers := {1, 2, 3},
all_heroes := Hero { name }
};
{ { my_string: 'This is a string', my_number: 42, several_numbers: {1, 2, 3}, all_heroes: { default::Hero {name: 'The Hulk'}, default::Hero {name: 'Iron Man'}, default::Hero {name: 'Spider-Man'}, default::Hero {name: 'Thor'}, default::Hero {name: 'Captain America'}, default::Hero {name: 'Black Widow'}, }, }, }
Note that the result is a singleton but each key corresponds to a set of values, which may have any cardinality.
All top-level EdgeQL statements (select
, insert
, update
, and
delete
) can be prefixed with a with
block. These blocks let you declare
standalone expressions that can be used in your query.
db> ... ...
with hero_name := "Iron Man"
select Hero { secret_identity }
filter .name = hero_name;
{default::Hero {secret_identity: 'Tony Stark'}}
For full documentation on with
, see EdgeQL > With.