4.2 - Schema Manager

The API and the ApacheDS server components must to keep schema elements available to interrogate and use. This is done through what we call a SchemaManager. It hides the internal structure of the schema objects from the users.



The SchemaManager stores all the Schema elements (AttributeTypes (e), ObjectClasses (e), … Internally, we store these elements into what is call a Registries. Registries are hives where each Schema Object is stored. Each schema element has a dedicated Registry associated with it. Think of it as a Map which returns a reference to a specific Schema Element according to its name or OID.

Note : 
Each Schema Element is properly defined by one of its names or <b>OID</b>. The <b>OID</b> must be unique across all schema elements, 
when the name can be used in different schema element (for instance, the <b>audio</b> <b>AttributeType</b> or <b>ObjectClass</b>)

From the user point of view, the SchemaManager is seen as a representation of the available LDAP schema elements. It can of course be extended, or modified, by adding or removing schema elements. For historic reasons, the schema elements are gathered into what we call a schema. Usually, this is what you load into a schemaManager

The server has one instance of a SchemaManager, which is used internally, and a users aren’t allowed to control it. On the client side, we can load a SchemaManager either from the server (which will be a duplicated instance), or from existing schema files. We can even create a brand new SchemaManager and fill it with anything needed.

The various pieces of the puzzle…

Creating a SchemaManager results in a complex structure being created, and involves a lot of other helper class. We will separate the description into three groups:

  • The elements stored in the SchemaManager
  • The containers in which those SchemaObject instances are stored, called Registries
  • The classes used to initialize the SchemaManager, called the SchemaLoader (which comes in various flavors)

Getting a SchemaManager

The very first thing we do to access the schema elements is to gain access to the SchemaManager. This can be done in many ways:

  • you can create one from scratch, and load it with the elements you want
  • you can use a default SchemaManager, with some default schema elements
  • you can create a SchemaManager, and load the schema elements from a destination
  • last, not least - and probably the most interesting possibility -, you can connect to a LDAP server and load the schema from it.

We will show how to proceed in each of these four use cases.

Using a SchemaManager

Let’s first assume you have an instance of a SchemaManager (we will see later how to get such an instance).