Functions take a set of arguments of specific types and return a single value of a specific type. They may be polymorphic, i.e. accept several argument type variations possibly returning different types, and may take a variable number of arguments. Function calls return null if arguments have invalid types, and an error if the function does not exist.

Known issue

Functions may throw errors rather than return null on type conflicts.


coalesce(<any>...) <any>

Takes a variable number of arguments of any type, and returns the first non-null argument if any, otherwise null - e.g. coalesce(null, 1, "a") returns 1.


count(<array>) <integer>

Returns the number of elements in the passed array, e.g. count([1,2,3]) returns 3.


defined(<any>) boolean

Returns true if the argument is non-null and not an empty array or object, otherwise false.


identity() string

Returns the identity (user ID) of the user performing the current action, or the special values <anonymous> for unauthenticated users and <system> for system-initiated actions.


length(<array|string>) <integer>

Returns the length of the argument, either the number of elements in an array or the number of Unicode characters in a string, e.g. length([1,2,3]) returns 3 and length("Hi! 👋") returns 5.


now() datetime

Returns the current time in ISO 8601-format with microsecond resolution in the UTC time zone, e.g. 2019-03-06T15:51:24.846513Z. The current time is stable within an operation such that multiple calls return identical values, and this generally refers to the start time of the operation except for listener queries which refer to the event's transaction time.


Mutations using query parameters triggers two separate operations internally: first execution of queries to determine which documents to update, then a transaction to actually update the documents. now() will return different times for these two operations, referring to the start time of each operation.


path(<string>) <path>

Coerces the passed string to a path, e.g. "a.b" in path("a.*").


references(<path|string>) <boolean>

Implicitly takes the document at the root of the current scope and recursively checks whether it contains any references to the given document ID. It is typically used in query filters, e.g. *[ references("abc") ] will return any documents that contains a reference to the document abc.


round(<integer|float>[, <integer>]) <integer|float>

Rounds the given number to the nearest integer, or to the number of decimal places given by the second, optional argument - e.g. round(3.14) yields 3 and round(3.14, 1) yields 3.1.


select(<pair|any>...) <any>

Used for conditionals, i.e. "if-else" expressions. Takes a variable number of arguments that are either pairs or any other type and iterates over them. When encountering a pair whose left-hand value evaluates to true, the right-hand value is returned immediately. When encountering a non-pair argument, that argument is returned immediately. Falls back to returning null.

For example, the following call returns "adult" if age >= 18, otherwise "teen" if age >= 13, otherwise "child":

  age >= 18 => "adult",
  age >= 13 => "teen",

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