Generic functions

Generic Functions

Name Description
CURRENT_DOCUMENT Returns the document currently being processed in the pipeline.
CONCAT Concatenates two or more values of same type.
LENGTH Calculates the length of a String, Bytes, Array, Vector, or Map.
REVERSE Reverses a String, Bytes, or Array.

CURRENT_DOCUMENT

Syntax:

current_document() -> MAP

Description:

Evaluates to a map that holds all fields defined in the current scope. This is useful when merging or aggregating multiple documents together or when wanting to dynamically inspect the field names in the document.

For example, to get a list of documents grouped by a field:

Node.js

const cities = await db.pipeline()
  .collection("/restaurants")
  .aggregate({
    groups: [ field("location.state").as("state") ],
    accumulators: [ arrayAgg(currentDocument().as("restaurants")) ]
   })
  .execute();

CONCAT

Syntax:

concat[T <: STRING | BYTES | ARRAY](values:T ...) -> T

Description:

Concatenates two or more values of same type.

Examples:

values concat(values)
"abc", "def" "abcdef"
[1, 2], [3, 4] [1, 2, 3, 4]
b"abc", b"def" b"abcdef"
"abc", [1,2,3], "ghi" error
[1,2,3] error
"abc", null null
Node.js
concat(constant("Author ID: "), field("authorId"));
test.firestore.js

Web

concat(constant("Author ID: "), field("authorId"));
test.firestore.js
Swift
let displayString = Constant("Author ID: ").concat([Field("authorId")])
PipelineSnippets.swift

Kotlin

val displayString = constant("Author ID: ").concat(field("authorId"))

DocSnippets.kt

Java

Expression displayString = constant("Author ID: ").concat(field("authorId"));
DocSnippets.java
Python
Constant.of("Author ID: ").concat(Field.of("authorId"))
firestore_pipelines.py

LENGTH

Syntax:

length[T <: STRING | BYTES | ARRAY | VECTOR | MAP](value: T) -> INT64

Description:

Calculates the length of a String, Bytes, Array, Vector, or Map value.

Examples:

value length(value)
"hello" 5
[1, 2, 3, 4] 4
b"abcde" 5
null null
1 error

REVERSE

Syntax:

reverse[T <: STRING | BYTES | ARRAY](value: T) -> T

Description:

Reverses a String, Bytes, or Array value.

Examples:

value reverse(value)
"hello" "olleh"
[1, 2, 3] [3, 2, 1]
b"abc" b"cba"
23 error
null null