SQL - CREATE CLASS

Creates a new class in the schema.

Syntax

CREATE CLASS <class> 
[ IF NOT EXISTS ]
[EXTENDS <super-class>] [CLUSTER <cluster-id>*] [CLUSTERS <total-cluster-number>] [ABSTRACT]
  • <class> Defines the name of the class you want to create. You must use a letter, underscore or dollar for the first character, for all other characters you can use alphanumeric characters, underscores and dollar.
  • IF NOT EXISTS Specifying this option, the class creation will just be ignored if the class already exists (instead of failing with an error)
  • <super-class> Defines the super-class you want to extend with this class.
  • <cluster-id> Defines in a comma-separated list the ID's of the clusters you want this class to use.
  • <total-cluster-number> Defines the total number of clusters you want to create for this class. The default value is 1. This feature was introduced in version 2.1.
  • ABSTRACT Defines whether the class is abstract. For abstract classes, you cannot create instances of the class.

In the event that a cluster of the same name exists in the cluster, the new class uses this cluster by default. If you do not define a cluster in the command and a cluster of this name does not exist, OrientDB creates one. The new cluster has the same name as the class, but in lower-case.

When working with multiple cores, it is recommended that you use multiple clusters to improve concurrency during inserts. To change the number of clusters created by default, ALTER DATABASE command to update the minimumclusters property. Beginning with version 2.1, you can also define the number of clusters you want to create using the CLUSTERS option when you create the class.

Examples

  • Create the class Account:

    orientdb> CREATE CLASS Account

  • Create the class Car to extend Vehicle:

    orientdb> CREATE CLASS Car EXTENDS Vehicle

  • Create the class Car, using the cluster ID of 10:

    orientdb> CREATE CLASS Car CLUSTER 10

  • Create the class Person as an abstract class:

    orientdb> CREATE CLASS Person ABSTRACT

Cluster Selection Strategies

When you create a class, it inherits the cluster selection strategy defined at the database-level. By default this is set to round-robin. You can change the database default using the ALTER DATABASE command and the selection strategy for the class using the ALTER CLASS command.

Supported Strategies:

StrategyDescription
defaultSelects the cluster using the class property defaultClusterId. This was the default selection strategy before version 1.7.
round-robinSelects the next cluster in a circular order, restarting once complete.
balancedSelects the smallest cluster. Allows the class to have all underlying clusters balanced on size. When adding a new cluster to an existing class, it fills the new cluster first. When using a distributed database, this keeps the servers balanced with the same amount of data. It calculates the cluster size every five seconds or more to avoid slow-downs on insertion.

For more information, see