Difference between revisions of "EclipseLink/UserGuide/SDO/Introduction to EclipseLink SDO (ELUG)"

Revision as of 11:21, 23 April 2009

This section introduces EclipseLink implementation of Service Data Objects (SDO) specification, as well as provides information on how you can use it in your application development.

Using SDO Metadata

SDO metadata is represented as Type and Property objects. You define the metadata at run time either programmatically, or from an XML schema.

Using Type

SDO Type acts similarly to a Class in Java, and provides much of the same metadata as the Java Reflection API provides for Java classes.

In EclipseLink, a Type wraps an object-XML mapping (OXM) descriptor (see ...).

A Type can have supertypes, which corresponds to the EclipseLink concept of an inheritance policy (see ...).

For more information, see Type API.

What You May Need to Know About Open Sequenced Type

...

What You May Need to Know About DataObject Types for Data Types

...

Using Property

SDO Property acts similarly to a property in Java and provides much of the same metadata as the Java Reflection API provides for Java fields or methods.

In EclipseLink, a Property wraps an object-XML mapping (see ...) in the following way:

• DataType=true + isMany=false (see OXM Direct Mapping (or an OXM Binary Mapping))
• DataType=true + isMany=true (see OXM Direct Collection Mapping (or an OXM Binary Collection Mapping))
• DataType=false + isMany=false + containment=true (see OXM Composite Object Mapping)
• DataType=false + isMany=true + containment=true (see OXM Composite Collection Mapping)
• DataType=false + isMany=false + containment=false (see OXM Reference Mapping)
• DataType=false + isMany=true + containment=false (see OXM Collection Reference Mapping)

For more information, see Property API.

Defining Metadata

You can use the following EclipseLink helper classes to define SDO metadata (information pending: document how the underlying EclipseLink metadata can be accessed and modified).

How to Define Metadata with EclipseLink XSDHelper

You use the XSDHelper to do the following:

• Define SDO metadata, where SDO metadata is derived from XML schemas.
• Generate XML schemas from SDO types.

You can customize metadata using the following annotations that you apply to the XML schema:

• Standard annotations (information pending: list them).
• EclipseLink annotations.

You can also use various APIs to determine the XML representation about the SDO metadata.

How to Define Metadata with EclipseLink TypeHelper

You use the TypeHelper to do the following:

• Look up SDO metadata.
• Programmatically define SDO metadata (note that this is not the typical usage for the TypeHelper).

Using Data

...

Using DataObject (see 17.2.6 “Mapping converters and transformers” in JITDG/ELUG)

DataObject in SDO corresponds to a Java Object (POJO). To define object-XML mappings, you map the DataObject to XML. You can create your DataObject as either dynamic (see Dynamic DataObject Examples), or static by applying a type-safe interface to it (see Static DataObject Examples). The DataObject provides an XPath-like (see ...) means of data access. For example, the following code is valid in SDO:

customerDO.getDataObject("contact-info/phone-number[2]"); 

The standard JAXB, however, would require the following:

customer.getContactInfo().getPhoneNumbers().get(1); 

For more information, see DataObject API

What You May Need to Know About Serialization in SDO (see 17.2.6.1 in JITDG/ELUG)

SDO has its own Java serialization format.

Using XMLDocument

When you marshall (save) to, or unmarshall (load from) XML a DataObject, the XMLDocument class contains information about the root of the XML document.

What You May Need to Know About Sequence, ChangeSummary, and DataGraph

The following SDO classes... :(information pending)

• Sequence
• ChangeSummary
• DataGraph -- essentially deprecated.