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

Revision as of 14:32, 28 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 SDOType wraps an object-XML mapping (OXM) descriptor.

A Type can have supertypes, which corresponds to the EclipseLink concept of inheritance policy (see Inheritance Policy in Descriptor API).

For more information, see Type API.

What You May Need to Know About Open Sequenced Type

For information, see OpenSequencedType.

What You May Need to Know About DataObjectType for Data Types

For information, see SDODataObjectType.

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 SDOProperty wraps an object-XML mapping in the following way:

• DataType=true + isMany=false

Corresponds to EclipseLink OXM direct mappings and OXM binary mappings.

• DataType=true + isMany=true

Corresponds to EclipseLink OXM direct collection mappings and OXM binary collection mappings.

• DataType=false + isMany=false + containment=true

Corresponds to EclipseLink OXM composite object mappings.

• DataType=false + isMany=true + containment=true

Corresponds to EclipseLink OXM composite collection mappings.

• DataType=false + isMany=false + containment=false

Corresponds to EclipseLink OXM reference mappings.

• DataType=false + isMany=true + containment=false

Corresponds to EclipseLink OXM collection reference mappings.

For more information, see Property API.

Defining Metadata

You can use the following EclipseLink helper classes to define SDO metadata:

• SDOXSDHelper
• SDOTypeHelper

Information pending: modifying and accessing the underlying EclipseLink metadata

For more information, see the following:

• XSDHelper API
• TypeHelper API

How to Define Metadata with EclipseLink SDOXSDHelper

You use the SDOXSDHelper 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
• EclipseLink annotations:
  • Information pending

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

How to Define Metadata with EclipseLink SDOTypeHelper

You use the SDOTypeHelper to do the following:

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

Using Data

You can use the following SDO classes to work with data:

• XSDHelper
• XMLDocument

Using DataObject

A DataObject in SDO corresponds to a Java Object (POJO). To define object-XML mappings, you map the DataObject to XML. You can create your data object 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 Mappings and XPath) 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); 

Note that you can use the EclipseLink XPathHelper to query data objects using an XPath expression.

For more information, see EclipseLinkSDODataObject API

What You May Need to Know About Serialization in SDO

SDO has its own Java serialization format. The DataObject implements the Serializable interface.

Information pending.

Using XMLDocument

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

For more information, see EclipseLink SDOXMLDocument API.

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

The following SDO classes allow you to obtain additional information about data objects:

• Sequence -- provides a list of properties and their corresponding values.
• ChangeSummary -- records changes to data objects.

Note that the DataGraph class has been deprecated.

For more information, see the following EclipseLink API:

• SDOSequence
• SDOChangeSummary

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