Miscellaneous functions in AQL

Control flow functions

FIRST_DOCUMENT()

FIRST_DOCUMENT(alternative, ...) → doc

Return the first alternative that is a document, and null if none of the alternatives is a document.

• alternative (any, repeatable): input of arbitrary type
• returns doc (object|null): document / object or null

FIRST_LIST()

FIRST_LIST(alternative, ...) → list

Return the first alternative that is an array, and null if none of the alternatives is an array.

• alternative (any, repeatable): input of arbitrary type
• returns list (array|null): array / list or null

MIN_MATCH()

MIN_MATCH(expr1, ... exprN, minMatchCount) → fulfilled

Match documents where at least minMatchCount of the specified AQL expressions are satisfied.

There is a corresponding MIN_MATCH() ArangoSearch function that can utilize View indexes.

• expr (expression, repeatable): any valid AQL expression
• minMatchCount (number): minimum number of expressions that should be satisfied
• returns fulfilled (bool): whether at least minMatchCount of the specified expressions are true

You can use MIN_MATCH() to filter if two out of three conditions evaluate to true for instance:

LET members = [
  { name: "Carol", age: 41, active: true },
  { name: "Doug", age: 56, active: true },
]
FOR doc IN members
  FILTER MIN_MATCH(LENGTH(doc.name) == 5, doc.age >= 50, doc.active, 2)
  RETURN doc

An equivalent filter expression without MIN_MATCH() would be more cumbersome:

  FILTER (LENGTH(doc.name) == 5 AND doc.age >= 50)
    OR (doc.age >= 50 AND doc.active)
    OR (doc.active AND LENGTH(doc.name) == 5)

NOT_NULL()

NOT_NULL(alternative, ...) → value

Return the first element that is not null, and null if all alternatives are null themselves. It is also known as COALESCE() in SQL.

• alternative (any, repeatable): input of arbitrary type
• returns value (any): first non-null parameter, or null if all arguments are null

Ternary operator

For conditional evaluation, check out the ternary operator.

Database functions

CHECK_DOCUMENT()

CHECK_DOCUMENT(document) → checkResult

Returns true if document is a valid document object, i.e. a document without any duplicate attribute names. Will return false for any non-objects/non-documents or documents with duplicate attribute names.

The primary use case for this function is to apply it on all documents in a given collection as follows:

FOR doc IN collection
  FILTER !CHECK_DOCUMENT(doc)
  RETURN JSON_STRINGIFY(doc)

This query will return all documents in the given collection with redundant attribute names and export them. This output can be used for subsequent cleanup operations.

• document (object): an arbitrary document / object
• returns checkResult (bool): true for any valid objects/documents without duplicate attribute names, and false for any non-objects/non-documents or objects/documents with duplicate attribute names

COLLECTION_COUNT()

COLLECTION_COUNT(coll) → count

Determine the amount of documents in a collection. LENGTH() is preferred.

COLLECTIONS()

COLLECTIONS() → docArray

Return an array of collections.

• returns docArray (array): each collection as a document with attributes name and _id in an array

COUNT()

This is an alias for LENGTH().

CURRENT_DATABASE()

CURRENT_DATABASE() → databaseName

Returns the name of the current database.

The current database is the database name that was specified in the URL path of the request (or defaults to _system database).

• returns databaseName (string): the current database name

CURRENT_USER()

CURRENT_USER() → userName

Return the name of the current user.

The current user is the user account name that was specified in the Authorization HTTP header of the request. It will only be populated if authentication on the server is turned on, and if the query was executed inside a request context. Otherwise, the return value of this function will be null.

• returns userName (string|null): the current user name, or null if authentication is disabled

DECODE_REV()

DECODE_REV(revision) → details

Decompose the specified revision string into its components. The resulting object has a date and a count attribute. This function is supposed to be called with the _rev attribute value of a database document as argument.

• revision (string): revision ID string
• returns details (object|null): object with two attributes date (string in ISO 8601 format) and count (integer number), or null

If the input revision ID is not a string or cannot be processed, the function issues a warning and returns null.

Please note that the result structure may change in future versions of ArangoDB in case the internal format of revision strings is modified. Please also note that the date value in the current result provides the date and time of when the document record was put together on the server, but not necessarily the time of insertion into the underlying storage engine. Therefore in case of concurrent document operations the exact document storage order cannot be derived unambiguously from the revision value. It should thus be treated as a rough estimate of when a document was created or last updated.

DECODE_REV( "_YU0HOEG---" )
// { "date" : "2019-03-11T16:15:05.314Z", "count" : 0 }

DOCUMENT()

Dynamically look up one or multiple documents from any collections, either using a collection name and one or more document keys, or one or more document identifiers. The collections do not need to be known at query compile time, they can be computed at runtime.

DOCUMENT(collection, id) → doc

Return the document identified by id (document key or identifier) from the specified collection.

If the document cannot be found, null will be returned. If there is a mismatch between the collection passed and the collection in the document identifier, then null will be returned, too.

The id parameter can also be an array of document keys or identifiers. In this case, the function will return an array of all documents that could be found. The results are not guaranteed to be in the requested order. Documents that could not be found are not indicated in the result (no null values) and do also not raise warnings.

• collection (string): name of a collection
• id (string|array): a document key, a document identifier, or an array of document keys, identifiers, or both
• returns doc (document|array|null): the found document (or null if it was not found), or an array of all found documents in any order

Examples

RETURN DOCUMENT( persons, "persons/alice" )

[ 
  { 
    "_key" : "alice", 
    "_id" : "persons/alice", 
    "_rev" : "_hg5kIDq---", 
    "name" : "Alice" 
  } 
]

RETURN DOCUMENT( persons, "alice" )

[ 
  { 
    "_key" : "alice", 
    "_id" : "persons/alice", 
    "_rev" : "_hg5kIE6---", 
    "name" : "Alice" 
  } 
]

RETURN DOCUMENT( persons, [ "persons/alice", "persons/bob" ] )

[ 
  [ 
    { 
      "_key" : "alice", 
      "_id" : "persons/alice", 
      "_rev" : "_hg5kIHO---", 
      "name" : "Alice" 
    }, 
    { 
      "_key" : "bob", 
      "_id" : "persons/bob", 
      "_rev" : "_hg5kIHO--_", 
      "name" : "Bob" 
    } 
  ] 
]

RETURN DOCUMENT( persons, [ "alice", "bob" ] )

[ 
  [ 
    { 
      "_key" : "alice", 
      "_id" : "persons/alice", 
      "_rev" : "_hg5kIIW---", 
      "name" : "Alice" 
    }, 
    { 
      "_key" : "bob", 
      "_id" : "persons/bob", 
      "_rev" : "_hg5kIIa---", 
      "name" : "Bob" 
    } 
  ] 
]

RETURN DOCUMENT( @@coll, @key ) 

{
  "@coll": "persons",
  "key": "alice"
}

[ 
  { 
    "_key" : "alice", 
    "_id" : "persons/alice", 
    "_rev" : "_hg5kIK2---", 
    "name" : "Alice" 
  } 
]

RETURN DOCUMENT( @@coll, @keys )

{
  "@coll": "persons",
  "keys": [
    "alice",
    "bob"
  ]
}

[ 
  [ 
    { 
      "_key" : "alice", 
      "_id" : "persons/alice", 
      "_rev" : "_hg5kINm---", 
      "name" : "Alice" 
    }, 
    { 
      "_key" : "bob", 
      "_id" : "persons/bob", 
      "_rev" : "_hg5kINm--_", 
      "name" : "Bob" 
    } 
  ] 
]

DOCUMENT(id) → doc

The function can also be used with a single id parameter as follows:

• id (string|array): a document identifier, or an array of identifiers
• returns doc (document|array|null): the found document (or null if it was not found), or an array of the found documents in any order

Examples

RETURN DOCUMENT("persons/alice")

[ 
  { 
    "_key" : "alice", 
    "_id" : "persons/alice", 
    "_rev" : "_hg5kIQO---", 
    "name" : "Alice" 
  } 
]

RETURN DOCUMENT( [ "persons/alice", "persons/bob" ] )

[ 
  [ 
    { 
      "_key" : "alice", 
      "_id" : "persons/alice", 
      "_rev" : "_hg5kIVi--A", 
      "name" : "Alice" 
    }, 
    { 
      "_key" : "bob", 
      "_id" : "persons/bob", 
      "_rev" : "_hg5kIVm---", 
      "name" : "Bob" 
    } 
  ] 
]

RETURN DOCUMENT( @key )

{
  "key": "persons/alice"
}

[ 
  { 
    "_key" : "alice", 
    "_id" : "persons/alice", 
    "_rev" : "_hg5kIZa---", 
    "name" : "Alice" 
  } 
]

RETURN DOCUMENT( @keys )

{
  "keys": [
    "persons/alice",
    "persons/bob"
  ]
}

[ 
  [ 
    { 
      "_key" : "alice", 
      "_id" : "persons/alice", 
      "_rev" : "_hg5kIe---_", 
      "name" : "Alice" 
    }, 
    { 
      "_key" : "bob", 
      "_id" : "persons/bob", 
      "_rev" : "_hg5kIeC---", 
      "name" : "Bob" 
    } 
  ] 
]

RETURN DOCUMENT( CONCAT("persons/", @key) )

{
  "key": "bob"
}

[ 
  { 
    "_key" : "bob", 
    "_id" : "persons/bob", 
    "_rev" : "_hg5kIhe--_", 
    "name" : "Bob" 
  } 
]

LENGTH()

LENGTH(coll) → documentCount

Determine the amount of documents in a collection.

It calls COLLECTION_COUNT() internally.

• coll (collection): a collection (not string)
• returns documentCount (number): the total amount of documents in coll

LENGTH() can also determine the number of elements in an array, the number of attribute keys of an object / document and the character length of a string.

SHARD_ID()

SHARD_ID(collection, shardKeys) → shardId

Return the shard in a collection that contains the specified shard keys.

• collection (string): a collection name
• shardKeys (object): a set of shard keys and values. Any missing shard key is substituted with the null value.
• returns shardId (string): the responsible shard for the specified shard keys in the given collection. On deployments other than clusters, the collection name itself is returned.

RETURN SHARD_ID("observations", { "time": "2021-05-25 07:15:00", "subject": "xh458", "val": 10 })

[ 
  "s6010020" 
]

Hash functions

HASH()

HASH(value) → hashNumber

Calculate a hash value for value.

• value (any): an element of arbitrary type
• returns hashNumber (number): a hash value of value

value is not required to be a string, but can have any data type. The calculated hash value will take the data type of value into account, so for example the number 1 and the string “1” will have different hash values. For arrays the hash values will be equal if the arrays contain exactly the same values (including value types) in the same order. For objects the same hash values will be created if the objects have exactly the same attribute names and values (including value types). The order in which attributes appear inside objects is not important for hashing.

The hash value returned by this function is a number. The hash algorithm is not guaranteed to remain the same in future versions of ArangoDB. The hash values should therefore be used only for temporary calculations, e.g. to compare if two documents are the same, or for grouping values in queries.

MINHASH()

MINHASH(values, numHashes) → hashes

Calculate MinHash signatures for the values using locality-sensitive hashing. The result can be used to approximate the Jaccard similarity of sets.

• values (array): an array with elements of arbitrary type to hash
• numHashes (number): the size of the MinHash signature. Must be greater or equal to 1. The signature size defines the probabilistic error (err = rsqrt(numHashes)). For an error amount that does not exceed 5% (0.05), use a size of 1 / (0.05 * 0.05) = 400.
• returns hashes (array): an array of strings with the encoded hash values

Examples

RETURN MINHASH(["foo", "bar", "baz"], 5)

[ 
  [ 
    "OmvEOSfAYs8", 
    "Jcz+LQgakgs", 
    "YfBzyXaSXIA" 
  ] 
]

MINHASH_COUNT()

MINHASH_COUNT(error) → numHashes

Calculate the number of hashes (MinHash signature size) needed to not exceed the specified error amount.

• error (number): the probabilistic error you can tolerate in the range [0, 1)
• returns numHashes (number): the required number of hashes to not exceed the specified error amount

Examples

RETURN MINHASH_COUNT(0.05)

[ 
  400 
]

MINHASH_ERROR()

MINHASH_ERROR(numHashes) → error

Calculate the error amount based on the number of hashes (MinHash signature size).

• numHashes (number): the number of hashes you want to check
• returns error (number): the probabilistic error to expect with the specified number of hashes

Examples

RETURN MINHASH_ERROR(400)

[ 
  0.05 
]

String-based hashing

See the following string functions:

• CRC32()
• FNV64()
• MD5()
• SHA1()
• SHA512()

Function calling

APPLY()

APPLY(functionName, arguments) → retVal

Dynamically call the function funcName with the arguments specified. Arguments are given as array and are passed as separate parameters to the called function.

Both built-in and user-defined functions can be called.

• funcName (string): a function name
• arguments (array, optional): an array with elements of arbitrary type
• returns retVal (any): the return value of the called function

APPLY( "SUBSTRING", [ "this is a test", 0, 7 ] )
// "this is"

CALL()

CALL(funcName, arg1, arg2, ... argN) → retVal

Dynamically call the function funcName with the arguments specified. Arguments are given as multiple parameters and passed as separate parameters to the called function.

Both built-in and user-defined functions can be called.

• funcName (string): a function name
• args (any, repeatable): an arbitrary number of elements as multiple arguments, can be omitted
• returns retVal (any): the return value of the called function

CALL( "SUBSTRING", "this is a test", 0, 4 )
// "this"

Other functions

ASSERT() / WARN()

ASSERT(expr, message) → retVal
WARN(expr, message) → retVal

The two functions evaluate an expression. In case the expression evaluates to true both functions will return true. If the expression evaluates to false ASSERT will throw an error and WARN will issue a warning and return false. This behavior allows the use of ASSERT and WARN in FILTER conditions.

• expr (expression): AQL expression to be evaluated
• message (string): message that will be used in exception or warning if expression evaluates to false
• returns retVal (bool): returns true if expression evaluates to true

FOR i IN 1..3 FILTER ASSERT(i > 0, "i is not greater 0") RETURN i
FOR i IN 1..3 FILTER WARN(i < 2, "i is not smaller 2") RETURN i

IN_RANGE()

IN_RANGE(value, low, high, includeLow, includeHigh) → included

Returns true if value is greater than (or equal to) low and less than (or equal to) high. The values can be of different types. They are compared as described in Type and value order and is thus identical to the comparison operators <, <=, > and >= in behavior.

• value (any): an element of arbitrary type
• low (any): minimum value of the desired range
• high (any): maximum value of the desired range
• includeLow (bool): whether the minimum value shall be included in the range (left-closed interval) or not (left-open interval)
• includeHigh (bool): whether the maximum value shall be included in the range (right-closed interval) or not (right-open interval)
• returns included (bool): whether value is in the range

If low and high are the same, but includeLow and/or includeHigh is set to false, then nothing will match. If low is greater than high nothing will match either.

LET value = 4
RETURN IN_RANGE(value, 3, 5, true, true)
/* same as:
   RETURN value >= 3 AND value <= 5
*/

[ 
  true 
]

FOR value IN 2..6
  RETURN { value, in_range: IN_RANGE(value, 3, 5, false, true) }
  /* same as:
     RETURN { value, in_range: value > 3 AND value <= 5 }
  */

[ 
  { 
    "value" : 2, 
    "in_range" : false 
  }, 
  { 
    "value" : 3, 
    "in_range" : false 
  }, 
  { 
    "value" : 4, 
    "in_range" : true 
  }, 
  { 
    "value" : 5, 
    "in_range" : true 
  }, 
  { 
    "value" : 6, 
    "in_range" : false 
  } 
]

LET coll = [
  { text: "fennel" },
  { text: "fox grape" },
  { text: "forest strawberry" },
  { text: "fungus" }
]
FOR doc IN coll
  FILTER IN_RANGE(doc.text,"fo", "fp", true, false) // values with prefix "fo"
  /* same as:
     FILTER doc.text >= "fo" AND doc.text < "fp"
  */
  RETURN doc

[ 
  { 
    "text" : "fox grape" 
  }, 
  { 
    "text" : "forest strawberry" 
  } 
]

Internal functions

The following functions are used during development of ArangoDB as a database system, primarily for unit testing. They are not intended to be used by end users, especially not in production environments.

FAIL()

FAIL(reason)

Let a query fail on purpose. Can be used in a conditional branch, or to verify if lazy evaluation / short circuiting is used for instance.

• reason (string): an error message
• returns nothing, because the query is aborted

RETURN 1 == 1 ? "okay" : FAIL("error") // "okay"
RETURN 1 == 1 || FAIL("error") ? true : false // true
RETURN 1 == 2 && FAIL("error") ? true : false // false
RETURN 1 == 1 && FAIL("error") ? true : false // aborted with error

NOOPT() / NOEVAL()

NOOPT(value) → retVal

No-operation that prevents certain query compile-time and run-time optimizations. Constant expressions can be forced to be evaluated at runtime with this. This function is marked as non-deterministic so its argument withstands query optimization.

NOEVAL(value) → retVal

Same as NOOPT(), except that it is marked as deterministic.

There is no need to call these functions explicitly, they are mainly used for internal testing.

• value (any): a value of arbitrary type
• returns retVal (any): value

// differences in execution plan (explain)
FOR i IN 1..3 RETURN (1 + 1)       // const assignment
FOR i IN 1..3 RETURN NOOPT(1 + 1)  // simple expression
FOR i IN 1..3 RETURN NOEVAL(1 + 1) // simple expression

RETURN NOOPT( 123 ) // evaluates 123 at runtime
RETURN NOOPT( CONCAT("a", "b") ) // evaluates concatenation at runtime

PASSTHRU()

PASSTHRU(value) → retVal

Simply returns its call argument unmodified. There is no need to call this function explicitly, it is mainly used for internal testing.

• value (any): a value of arbitrary type
• returns retVal (any): value

SCHEMA_GET()

SCHEMA_GET(collection) → schema

Return the schema definition as defined in the properties of the specified collection.

• collection (string): name of a collection
• returns schema (object): schema definition object

RETURN SCHEMA_GET("myColl")

SCHEMA_VALIDATE()

SCHEMA_VALIDATE(doc, schema) → result

Test if the given document is valid according to the schema definition.

• doc (doc): document
• schema (object): schema definition object
• returns result (object): an object with the following attributes:
  • valid (bool): true if the document fulfills the schema’s requirements, otherwise it will be false and errorMessage will be set
  • errorMessage (string): details about the validation failure

If the input document doc is not an object, the function will return a null value and register a warning in the query.

Using an empty schema object is equivalent to specifying a schema value of null, which will make all input objects successfully pass the validation.

SLEEP()

SLEEP(seconds) → null

Wait for a certain amount of time before continuing the query.

• seconds (number): amount of time to wait
• returns a null value

SLEEP(1)    // wait 1 second
SLEEP(0.02) // wait 20 milliseconds

V8()

V8(expression) → retVal

No-operation that enforces the usage of the V8 JavaScript engine. There is no need to call this function explicitly, it is mainly used for internal testing.

• expression (any): arbitrary expression
• returns retVal (any): the return value of the expression

// differences in execution plan (explain)
FOR i IN 1..3 RETURN (1 + 1)          // const assignment
FOR i IN 1..3 RETURN V8(1 + 1)        // simple expression

VERSION()

VERSION() → serverVersion

Returns the server version as a string. In a cluster, returns the version of the Coordinator.

• returns serverVersion (string): the server version string

RETURN VERSION()        // e.g. "3.10.0"