Generic Functions Reference

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
Android

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

Java
Android

 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

What's next

See the Pipeline Queries overview

Generic Functions Reference