Control flow functions

AQL offers the following functions to let the user control the flow of operations:

• NOT_NULL(alternative, …): Returns the first alternative that is not null, and null if all alternatives are null themselves

• FIRST_LIST(alternative, …): Returns the first alternative that is an array, and null if none of the alternatives is an array

• FIRST_DOCUMENT(alternative, …): Returns the first alternative that is a document, and null if none of the alternatives is a document

Miscellaneous functions

Finally, AQL supports the following functions that do not belong to any of the other function categories:

• COLLECTIONS(): Returns an array of collections. Each collection is returned as a document with attributes name and _id

• CURRENT_USER(): Returns 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.

• DOCUMENT(collection, id): Returns the document which is uniquely identified by the id. ArangoDB will try to find the document using the _id value of the document in the specified collection. If there is a mismatch between the collection passed and the collection specified in id, then null will be returned. Additionally, if the collection matches the collection value specified in id but the document cannot be found, null will be returned. This function also allows id to be an array of ids. In this case, the function will return an array of all documents that could be found.

Examples

  DOCUMENT(users, "users/john")
  DOCUMENT(users, "john")

  DOCUMENT(users, [ "users/john", "users/amy" ])
  DOCUMENT(users, [ "john", "amy" ])

Note: The DOCUMENT function is polymorphic since ArangoDB 1.4. It can now be used with a single parameter id as follows:

• DOCUMENT(id): In this case, id must either be a document handle string (consisting of collection name and document key) or an array of document handle strings, e.g.

  DOCUMENT("users/john")
  DOCUMENT([ "users/john", "users/amy" ])
  

• CALL(function, arg1, …, argN): Dynamically calls the function with name function with the arguments specified. Both built-in and user-defined functions can be called. Arguments are passed as separate parameters to the called function.

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

• APPLY(function, arguments): Dynamically calls the function with name function with the arguments specified. Both built-in and user-defined functions can be called. Arguments are passed as separate parameters to the called function.

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