HTTP Interface for Collections

This is an introduction to ArangoDB’s HTTP interface for collections.

Collections

A collection consists of documents. It is uniquely identified by its collection identifier. It also has a unique name that clients should use to identify and access it. Collections can be renamed. This will change the collection name, but not the collection identifier. Collections have a type that is specified by the user when the collection is created. There are currently two types: document and edge. The default type is document.

Collection Identifier

A collection identifier lets you refer to a collection in a database. It is a string value and is unique within the database. Clients should use a collection’s unique name to access a collection instead of its identifier. ArangoDB currently uses 64bit unsigned integer values to maintain collection ids internally. When returning collection ids to clients, ArangoDB will put them into a string to ensure the collection id is not clipped by clients that do not support big integers. Clients should treat the collection ids returned by ArangoDB as opaque strings when they store or use them locally.

Collection Name

A collection name identifies a collection in a database. It is a string and is unique within the database. Unlike the collection identifier it is supplied by the creator of the collection. The collection name must consist of letters, digits, and the _ (underscore) and - (dash) characters only. Please refer to Naming Conventions in ArangoDB for more information on valid collection names.

Key Generator

ArangoDB allows using key generators for each collection. Key generators have the purpose of auto-generating values for the _key attribute of a document if none was specified by the user. By default, ArangoDB will use the traditional key generator. The traditional key generator will auto-generate key values that are strings with ever-increasing numbers. The increment values it uses are non-deterministic.

Contrary, the auto increment key generator will auto-generate deterministic key values. Both the start value and the increment value can be defined when the collection is created. The default start value is 0 and the default increment is 1, meaning the key values it will create by default are:

1, 2, 3, 4, 5, …

When creating a collection with the auto increment key generator and an increment of 5, the generated keys would be:

1, 6, 11, 16, 21, …

The auto-increment values are increased and handed out on each document insert attempt. Even if an insert fails, the auto-increment value is never rolled back. That means there may exist gaps in the sequence of assigned auto-increment values if inserts fails.

The basic operations (create, read, update, delete) for documents are mapped to the standard HTTP methods (POST, GET, PUT, DELETE).

Address of a Collection

All collections in ArangoDB have a unique identifier and a unique name. ArangoDB internally uses the collection’s unique identifier to look up collections. This identifier however is managed by ArangoDB and the user has no control over it. In order to allow users use their own names, each collection also has a unique name, which is specified by the user. To access a collection from the user perspective, the collection name should be used, i.e.:

http://server:port/_api/collection/collection-name

For example: Assume that the collection identifier is 7254820 and the collection name is demo, then the URL of that collection is:

http://localhost:8529/_api/collection/demo