Types​

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Type expressions​

Type expressions are exactly what they sound like: EdgeQL expressions that refer to a type. Most commonly, these are simply the names of established types: str, int64, BlogPost, etc. Arrays and tuples have a dedicated type syntax.

For additional details on type syntax, see Schema > Primitive Types.

Type casting​

Type casting is used to convert primitive values into another type. Casts are indicated with angle brackets containing a type expression.

db> 

select <str>10;

{"10"}

db> 

select <bigint>10;

{10n}

db> 

select <array<str>>[1, 2, 3];

{['1', '2', '3']}

db> 

select <tuple<str, float64, bigint>>(1, 2, 3);

{('1', 2, 3n)}

Type casts are useful for declaring literals for types like datetime, uuid, and int16 that don't have a dedicated syntax.

db> 

select <datetime>'1999-03-31T15:17:00Z';

{<datetime>'1999-03-31T15:17:00Z'}

db> 

select <int16>42;

{42}

db> 

select <uuid>'89381587-705d-458f-b837-860822e1b219';

{89381587-705d-458f-b837-860822e1b219}

There are limits to what values can be cast to a certain type. In some cases two types are entirely incompatible, like bool and int64; in other cases, the source data must be in a particular format, like casting str to datetime. For a comprehensive table of castability, see Standard Library > Casts.

Type casts can only be used on primitive expressions, not object type expressions. Every object stored in the database is strongly and immutably typed; you can't simply convert an object to an object of a different type.

db> 

select <BlogPost>10;

QueryError: cannot cast 'std::int64' to 'default::BlogPost'

db> 

select <int64>'asdf';

InvalidValueError: invalid input syntax for type std::int64: "asdf"

db> 

select <int16>100000000000000n;

NumericOutOfRangeError: std::int16 out of range

You can cast a UUID into an object:

db> 

select <Hero><uuid>'01d9cc22-b776-11ed-8bef-73f84c7e91e7';

{default::Hero {id: 01d9cc22-b776-11ed-8bef-73f84c7e91e7}}

If you try to cast a UUID that no object of the type has as its id property, you'll get an error:

db> 

select <Hero><uuid>'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa';

gel error: CardinalityViolationError: 'default::Hero' with id 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa' does not exist

Type intersections​

All elements of a given set have the same type; however, in the context of sets of objects, this type might be abstract and contain elements of multiple concrete subtypes. For instance, a set of Media objects may contain both Movie and TVShow objects.

db> 

select Media;

{
  default::Movie {id: 9d2ce01c-35e8-11ec-acc3-83b1377efea0},
  default::Movie {id: 3bfe4900-3743-11ec-90ee-cb73d2740820},
  default::TVShow {id: b0e0dd0c-35e8-11ec-acc3-abf1752973be},
}

We can use the type intersection operator to restrict the elements of a set by subtype.

db> 

select Media[is Movie];

{
  default::Movie {id: 9d2ce01c-35e8-11ec-acc3-83b1377efea0},
  default::Movie {id: 3bfe4900-3743-11ec-90ee-cb73d2740820},
}

Logically, this computes the intersection of the Media and Movie sets; since only Movie objects occur in both sets, this can be conceptualized as a "filter" that removes all elements that aren't of type Movie.

Type checking​

The [is foo] "type intersection" syntax should not be confused with the type checking operator is.

db> 

select 5 is int64;

{true}

db> 

select {3.14, 2.718} is not int64;

{true, true}

db> 

select Media is Movie;

{true, true, false}

The typeof operator​

The type of any expression can be extracted with the typeof operator. This can be used in any expression that expects a type.

db> 

select <typeof 5>'100';

{100}

db> 

select "tuna" is typeof "trout";

{true}

Introspection​

The entire type system of Gel is stored inside Gel. All types are introspectable as instances of the schema::Type type. For a set of introspection examples, see Guides > Introspection.