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Select​

The select command retrieves or computes a set of values. We’ve already seen simple queries that select primitive values.

Copy
db> 
select 'hello world';
{'hello world'}
Copy
db> 
select [1, 2, 3];
{[1, 2, 3]}
Copy
db> 
select {1, 2, 3};
{1, 2, 3}

With the help of a with block, we can add filters, ordering, and pagination clauses.

Copy
db> 
... 
... 
with x := {1, 2, 3, 4, 5}
select x
filter x >= 3;
{3, 4, 5}
Copy
db> 
... 
... 
with x := {1, 2, 3, 4, 5}
select x
order by x desc;
{5, 4, 3, 2, 1}
Copy
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:

Copy
db> 
... 
select x := {1, 2, 3, 4, 5}
filter x >= 3;




Selecting objects​


However most queries are selecting objects that live in the database. For
                demonstration purposes, the queries below assume the following schema.


Copy
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;
  }
}







Selecting objects​


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.


Copy
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"},
]





Shapes​


To specify which properties to select, we attach a shape to Hero. A
                    shape can be attached to any object type expression in EdgeQL.


Copy
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​


Nested shapes can be used to fetch linked objects and their properties. Here we
                    fetch all Villain objects and their nemeses.


Copy
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.


Copy
db> 
... 
... 
... 
select Hero {
  name,
  villains: { name }
};
{
  default::Hero {
    name: 'Spider-Man',
    villains: {
      default::Villain {name: 'Green Goblin'},
      default::Villain {name: 'Doc Ock'},
    },
  },
  ...
}









Filtering​


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.


Copy
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.


Copy
db> 
... 
select Villain {name}
filter .name = "Doc Ock";
{default::Villain {name: 'Doc Ock'}}




Filtering by ID​


To filter by id, remember to cast the desired ID to uuid:


Copy
db> 
... 
select Villain {id, name}
filter .id = <uuid>"b233ca98-3c23-11ec-b81f-6ba8c4f0084e";
{
  default::Villain {
    id: 'b233ca98-3c23-11ec-b81f-6ba8c4f0084e',
    name: 'Doc Ock'
  }
}






Nested filters​


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.


Copy
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.









Ordering​


Order the result of a query with an order by clause.


Copy
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.




Copy
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.









Computed fields​


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.


Copy
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.


Copy
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',
    },
  },
  ...
}





Backlinks​


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.


Copy
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.


Copy
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.


Copy
select Hero {
  name,
  movies: { title }
} filter .name = "Iron Man";






Subqueries​


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.


Copy
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'},
    },
  },
  ...
}









Polymorphic queries​



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.




Polymorphic sets​


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).


Copy
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.


Copy
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'},
    },
  },
}






Polymorphic fields​


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.


Copy
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.


Copy
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: {},
  },
  ...
}






Filtering polymorphic links​


Relatedly, it’s possible to filter polymorphic links by subtype. Below, we
                    exclusively fetch the Movie.characters of type Hero.


Copy
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'}},
  },
  ...
}









Free objects​


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.


Copy
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.







With block​


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.


Copy
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.







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