Operator Delegates

Table of Contents
  1. Introduction
  2. Operator Delegate Interfaces
  3. Operator Delegate Registry
  4. Operator Delegate Lookup
  5. Roadmap

Introduction

Tree-ware has default handling for entities defined in a meta-model. But sometimes there is a need to handle a particular entity in a custom way. For example, consider the following entity for the latitude/longitude of a location:

{
  "name": "point",
  "fields": [
    {
      "name": "latitude",
      "type": "double"
    },
    {
      "name": "longitude",
      "type": "double"
    }
  ]
}

Tree-ware’s default handling would be to use two numeric columns to store the fields of this entity in a DB. But if the DB has support for geospatial columns, then those two fields might have to be saved in a single geospatial column.

To permit the above custom handling, model operators in tree-ware can delegate handling of entities to operator-specific delegates.

Operator Delegate Interfaces

Model operators support custom handling of entities by defining and using operator-specific delegate interfaces.

Operator Delegate Registry

Implementations of operator delegate interfaces must be registered in a delegate registry when the system starts. The registration must identify the entity in the meta-model, the operator, and provide an implementation for that operator’s delegate interface.

The entity is identified by its fully-qualified-name in the meta-model. For example, if the point entity in the example above is defined in a meta-model package called geo, then its fully-qualified-name is /geo/point.

Operators are defined in different libraries and identifying them with strings cannot guarantee uniqueness. So operators define objects that extend the OperatorId marker interface, and these objects are used as operators IDs.

There are two registries for performance reasons:

  1. OperatorDelegateRegistry is the main registry and is used for registering entity IDs, operator IDs, and delegate implementations.
  2. DelegateRegistry contains the entity ID to delegate implementation mappings for a single operator in order to speed up lookups in that operator.

Operator Delegate Lookup

Model operators are provided access to the operator delegate registry. When they visit an entity, they look up the registry for a delegate for that entity, and if one is available, they delegate handling of the entity to that delegate.

Roadmap

  • To reduce deployment package size, the build should automatically include only the delegates that are needed based on entities in the meta-model and operators used in the system.