Database Methods

Collection

returns a single collection or null db._collection(collection-name)

Returns the collection with the given name or null if no such collection exists.

db._collection(collection-identifier)

Returns the collection with the given identifier or null if no such collection exists. Accessing collections by identifier is discouraged for end users. End users should access collections using the collection name.

Examples

Get a collection by name:

arangosh> db._collection("demo");
[ArangoCollection 92, "demo" (type document, status loaded)]

Get a collection by id:

arangosh> db._collection(123456);
[ArangoCollection 123456, "demo" (type document, status loaded)]

Unknown collection:

arangosh> db._collection("unknown");
null

Create

creates a new document or edge collection db._create(collection-name)

Creates a new document collection named collection-name. If the collection name already exists or if the name format is invalid, an error is thrown. For more information on valid collection names please refer to the naming conventions.

db._create(collection-name, properties)

properties must be an object with the following attributes:

  • waitForSync (optional, default false): If true creating a document will only return after the data was synced to disk.

  • journalSize (optional, default is a configuration parameter: The maximal size of a journal or datafile. Note that this also limits the maximal size of a single object. Must be at least 1MB.

  • isSystem (optional, default is false): If true, create a system collection. In this case collection-name should start with an underscore. End users should normally create non-system collections only. API implementors may be required to create system collections in very special occasions, but normally a regular collection will do.

  • isVolatile (optional, default is false): If true then the collection data is kept in-memory only and not made persistent. Unloading the collection will cause the collection data to be discarded. Stopping or re-starting the server will also cause full loss of data in the collection. The collection itself will remain however (only the data is volatile). Setting this option will make the resulting collection be slightly faster than regular collections because ArangoDB does not enforce any synchronization to disk and does not calculate any CRC checksums for datafiles (as there are no datafiles). This option is meaningful for the MMFiles storage engine only.

  • keyOptions (optional): additional options for key generation. If specified, then keyOptions should be a JSON object containing the following attributes (note: some of them are optional):

    • type: specifies the type of the key generator. The currently available generators are traditional and autoincrement. (note: autoincrement is currently only supported for non-sharded collections)
    • allowUserKeys: if set to true, then it is allowed to supply own key values in the _key attribute of a document. If set to false, then the key generator will solely be responsible for generating keys and supplying own key values in the _key attribute of documents is considered an error.
    • increment: increment value for autoincrement key generator. Not used for other key generator types.
    • offset: initial offset value for autoincrement key generator. Not used for other key generator types.

  • numberOfShards (optional, default is 1): in a cluster, this value determines the number of shards to create for the collection. In a single server setup, this option is meaningless.

  • shardKeys (optional, default is [ "_key" ]): in a cluster, this attribute determines which document attributes are used to determine the target shard for documents. Documents are sent to shards based on the values they have in their shard key attributes. The values of all shard key attributes in a document are hashed, and the hash value is used to determine the target shard. Note that values of shard key attributes cannot be changed once set. This option is meaningless in a single server setup.

    When choosing the shard keys, one must be aware of the following rules and limitations: In a sharded collection with more than one shard it is not possible to set up a unique constraint on an attribute that is not the one and only shard key given in shardKeys. This is because enforcing a unique constraint would otherwise make a global index necessary or need extensive communication for every single write operation. Furthermore, if _key is not the one and only shard key, then it is not possible to set the _key attribute when inserting a document, provided the collection has more than one shard. Again, this is because the database has to enforce the unique constraint on the _key attribute and this can only be done efficiently if this is the only shard key by delegating to the individual shards.

  • replicationFactor (optional, default is 1): in a cluster, this attribute determines how many copies of each shard are kept on different DBServers. The value 1 means that only one copy (no synchronous replication) is kept. A value of k means that k-1 replicas are kept. Any two copies reside on different DBServers. Replication between them is synchronous, that is, every write operation to the "leader" copy will be replicated to all "follower" replicas, before the write operation is reported successful.

    If a server fails, this is detected automatically and one of the servers holding copies take over, usually without an error being reported.

  • distributeShardsLike distribute the shards of this collection cloning the shard distribution of another.

    When using the Enterprise version of ArangoDB the replicationFactor may be set to "satellite" making the collection locally joinable on every database server. This reduces the number of network hops dramatically when using joins in AQL at the costs of reduced write performance on these collections.

db._create(collection-name, properties, type)

Specifies the optional type of the collection, it can either be document or edge. On default it is document. Instead of giving a type you can also use db._createEdgeCollection or db._createDocumentCollection.

db._create(collection-name, properties[, type], options)

As an optional third (if the type string is being omitted) or fourth parameter you can specify an optional options map that controls how the cluster will create the collection. These options are only relevant at creation time and will not be persisted:

  • waitForSyncReplication (default: true) When enabled the server will only report success back to the client if all replicas have created the collection. Set to false if you want faster server responses and don't care about full replication.

  • enforceReplicationFactor (default: true) When enabled which means the server will check if there are enough replicas available at creation time and bail out otherwise. Set to false to disable this extra check.

Examples

With defaults:

arangosh> c = db._create("users");
arangosh> c.properties();
show execution results

With properties:

arangosh> c = db._create("users", { waitForSync : true,
........> journalSize : 1024 * 1204});
arangosh> c.properties();
show execution results

With a key generator:

arangosh> db._create("users",
........> { keyOptions: { type: "autoincrement", offset: 10, increment: 5 } });
arangosh> db.users.save({ name: "user 1" });
arangosh> db.users.save({ name: "user 2" });
arangosh> db.users.save({ name: "user 3" });
show execution results

With a special key option:

arangosh> db._create("users", { keyOptions: { allowUserKeys: false } });
arangosh> db.users.save({ name: "user 1" });
arangosh> db.users.save({ name: "user 2", _key: "myuser" });
arangosh> db.users.save({ name: "user 3" });
show execution results

creates a new edge collection db._createEdgeCollection(collection-name)

Creates a new edge collection named collection-name. If the collection name already exists an error is thrown. The default value for waitForSync is false.

db._createEdgeCollection(collection-name, properties)

properties must be an object with the following attributes:

  • waitForSync (optional, default false): If true creating a document will only return after the data was synced to disk.
  • journalSize (optional, default is "configuration parameter"): The maximal size of a journal or datafile. Note that this also limits the maximal size of a single object and must be at least 1MB.

creates a new document collection db._createDocumentCollection(collection-name)

Creates a new document collection named collection-name. If the document name already exists and error is thrown.

All Collections

returns all collections db._collections()

Returns all collections of the given database.

Examples

arangosh> db._collections();
show execution results

Collection Name

selects a collection from the vocbase db.collection-name

Returns the collection with the given collection-name. If no such collection exists, create a collection named collection-name with the default properties.

Examples

arangosh> db.example;
[ArangoCollection 16616, "example" (type document, status loaded)]

Drop

drops a collection db._drop(collection)

Drops a collection and all its indexes and data.

db._drop(collection-identifier)

Drops a collection identified by collection-identifier with all its indexes and data. No error is thrown if there is no such collection.

db._drop(collection-name)

Drops a collection named collection-name and all its indexes. No error is thrown if there is no such collection.

db._drop(collection-name, options)

In order to drop a system collection, one must specify an options object with attribute isSystem set to true. Otherwise it is not possible to drop system collections.

Note: cluster collection, which are prototypes for collections with distributeShardsLike parameter, cannot be dropped.

Examples

Drops a collection:

arangosh> col = db.example;
[ArangoCollection 16711, "example" (type document, status loaded)]
arangosh> db._drop(col);
arangosh> col;
[ArangoCollection 16711, "example" (type document, status loaded)]

Drops a collection identified by name:

arangosh> col = db.example;
[ArangoCollection 16722, "example" (type document, status loaded)]
arangosh> db._drop("example");
arangosh> col;
[ArangoCollection 16722, "example" (type document, status deleted)]

Drops a system collection

arangosh> col = db._example;
[ArangoCollection 16733, "_example" (type document, status loaded)]
arangosh> db._drop("_example", { isSystem: true });
arangosh> col;
[ArangoCollection 16733, "_example" (type document, status deleted)]

Truncate

truncates a collection db._truncate(collection)

Truncates a collection, removing all documents but keeping all its indexes.

db._truncate(collection-identifier)

Truncates a collection identified by collection-identified. No error is thrown if there is no such collection.

db._truncate(collection-name)

Truncates a collection named collection-name. No error is thrown if there is no such collection.

Examples

Truncates a collection:

arangosh> col = db.example;
arangosh> col.save({ "Hello" : "World" });
arangosh> col.count();
arangosh> db._truncate(col);
arangosh> col.count();
show execution results

Truncates a collection identified by name:

arangosh> col = db.example;
arangosh> col.save({ "Hello" : "World" });
arangosh> col.count();
arangosh> db._truncate("example");
arangosh> col.count();
show execution results

© ArangoDB - the native multi-model NoSQL database