View source for Introduction to EclipseLink Support for Oracle Spatial (ELUG)

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This section provides an overview of the EclipseLink support for Oracle Spatial, as well as demonstrates the ways to extend EclipseLink to support the mapping and querying of Oracle Spatial columns (<tt>MDSYS.SDO_GEOMETRY</tt>).

For more information about Oracle Spatial, see <tt>http://www.oracle.com/technology/products/spatial/index.html</tt>



==EclipseLink Support for Oracle Spatial==

EclipseLink provides support for direct mappings of database columns of type <tt>MDSYS.SDO_GEOMETRY</tt> to attributes of the <tt>oracle.spatial.geometry.JGeometry</tt> data type. Because this conversion requires an active JDBC connection, perform the conversion in the database platform (see [[Introduction%20to%20Data%20Access%20(ELUG)#Database Platforms|Database Platforms]]) during retrieval from the JDBC result set. Then you must convert into a <tt>STRUCT</tt> type (for writing back into a SQL statement).

Consider the following:
* You cannot express the <tt>JGeometry</tt> data type using literal SQL–always convert it to a <tt>STRUCT</tt> type, and then bind.
* The object-relational data type structure mapping (see [[Introduction%20to%20Object-Relational%20Data%20Type%20Mappings%20(ELUG)#Object-Relational Data Type Structure Mapping|Object-Relational Data Type Structure Mapping]]) enables EclipseLink to build a Java object from the returned <tt>STRUCT</tt> type–instead, allow <tt>JGeometry</tt> to perform the conversion.

EclipseLink also provides support for spatial operators (see [[#How to Perform Queries Using Spatial Operator Expressions|How to Perform Queries Using Spatial Operator Expressions]]) through the EclipseLink expression framework (see [[Introduction%20to%20EclipseLink%20Expressions%20(ELUG)#Introduction to EclipseLink Expressions|Introduction to EclipseLink Expressions]]), as well as for custom object types that wrap <tt>SDO_GEOMETRY</tt>.

For information on configuring OC4J application server to use the EclipseLink structure converter, see ''Oracle Fusion Middleware Administration and Application Deployment Guide for Oracle Containers for Java EE''.

For information on using EclipseLink structure converter with other application servers (for example, JBoss, BEA WebLogic Server or SunAS), see the relevant server documentation.

==Using Structure Converters==
In EclipseLink, a <tt>org.eclipse.persistence.platform.database.DatabasePlatform</tt> (see [[Introduction%20to%20Data%20Access%20(ELUG)#Database Platforms|Database Platforms]]) stores a list of structure converters.

To create a custom converter, implement the <tt>org.eclipse.persistence.platform.database.converters.StructConverter</tt> interface and register it on your direct-to-field mapping (see [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Direct-to-Field Mapping|Direct-to-Field Mapping]]).

To use the <tt>StructConverter</tt>, do the following:
# Configure the database platform (see [[#How to Configure the Database Platform to Use Structure Convertes|How to Configure the Database Platform to Use Structure Convertes]]).
# Set up a mapping (see [[#How to Set Up Mappings Using Structure Converters|How to Set Up Mappings Using Structure Converters]]).


===How to Configure the Database Platform to Use Structure Convertes===
EclipseLink uses a database platform (see [[Introduction%20to%20Data%20Access%20(ELUG)#Database Platforms|Database Platforms]]) to control the usage of database vendor-specific and version-specific operations such as SQL dialect, stored procedure calls, sequencing, as well as platform-specific type handling. You need to configure the platform to allow EclipseLink to use the advanced features of the database.

To add your structure converter to the <tt>DatabasePlatform</tt>, call <tt>addStructConverter(StructConverter converter)</tt> method of the <tt>DatabasePlatform</tt>. Call this method within your EclipseLink session (server or database) prior to the session login (see [[Configuring%20a%20Session%20(ELUG)#Configuring a Session Login|Configuring a Session Login]]).

===How to Set Up Mappings Using Structure Converters===
Use direct-to-field mappings (see [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Direct-to-Field Mapping|Direct-to-Field Mapping]]) to map your <tt>STRUCT</tt> types. For each mapping that maps to the type defined by the structure converter, set its field type to the <tt>STRUCT</tt> data type, as follows:
 mapping.setFieldType(java.sql.Types.STRUCT);

==Using JGeometry==

To use the <tt>oracle.spatial.geometry.JGeometry</tt>, do the following:

# Configure the database platform (see [[#How to Configure the Database Platform to Use JGeometry|How to Configure the Database Platform to Use JGeometry]]).
# Set up a mapping (see [[#How to Map JGeometry Attributes|How to Map JGeometry Attributes]]).

You can query your mapped entities with expressions that use Spatial operators. For more information, see [[#How to Perform Queries Using Spatial Operator Expressions|How to Perform Queries Using Spatial Operator Expressions]].



===How to Configure the Database Platform to Use JGeometry===
To configure the database platform, add a structure converter in a form of the <tt>oracle.toplink.platform.database.oracle.converters.JGeometryConverter</tt> as follows:
 
 databasePlatform.addStructConverter(new JGeometryConverter());

You must configure this platform within your EclipseLink session prior to the session login (see [[Configuring%20a%20Session%20(ELUG)|Configuring a Session Login]]).



===How to Map JGeometry Attributes===
Use direct-to-field mappings (see [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Direct-to-Field Mapping|Direct-to-Field Mapping]]) to map your <tt>STRUCT</tt> types. For each mapping that maps to the type defined by the structure converter (<tt>JGeometry</tt>), set its field type to the <tt>STRUCT</tt> data type, as follows:
 mapping.setFieldType(java.sql.Types.STRUCT);



===How to Perform Queries Using Spatial Operator Expressions===
With the configured database platform, you can read and write persistent entities with <tt>JGeometry</tt> attributes mapped to <tt>SDO_GEOMETRY</tt> columns. With this support, you can query for these mapped entities with native SQL queries using Oracle Spatial operators.

Spatial operators are special SQL functions supported by the Oracle Database to enable querying and comparison of columns containing geometry types. The spatial operators take the following format:
 <SPATIAL-OP>(geometry1, geometry2, parameters) = 'TRUE' 

For more information on spatial operators, see ''Oracle Spatial API Documentation'' at <tt>http://download.oracle.com/docs/cd/B28359_01/appdev.111/b28401/toc.htm</tt>.

EclipseLink provides the expression support for the following Spatial operators:
* <tt>SDO_WITHIN_DISTANCE</tt>
* <tt>SDO_RELATE</tt>
* <tt>SDO_FILTER</tt>
* <tt>SDO_NN</tt>

Use the following methods of the <tt>org.eclipse.persistence.expressions.spatial.SpatialExpressionFactory</tt> class to build expressions that use Spatial operators:
* <tt>withinDistance</tt>
* <tt>relate</tt>
* <tt>filter</tt>
* <tt>nearestNeighbor</tt>

All these methods have the following common set of parameters:
# an expression (org.eclipse.persistence.expressions.Expression) that points to <tt>JGeometry</tt><nowiki>;</nowiki>
# <tt>JGeometry</tt> object or an <tt>Expression</tt><nowiki>;</nowiki>
# an <tt>org.eclipse.persistence.expressions.spatial.SpatialParameters</tt> object that defines the parameters to the function call.

The <tt>SpatialParameters</tt> class provides convenience methods that let you set the parameters representing the following:
* minimum resolution;
* maximum resolution;
* units;
* distance;
* query type;
* masks;
* <tt>String</tt> of parameters.


This example demonstrates how to construct a Spatial operator expression, and then relate it to an existing <tt>JGeometry</tt> with <tt>SpatialParameters</tt> created using a <tt>String</tt>.<br>

<span id="Example 108-1"></span>


''''' Relating an Expression Using String of Spatial Parameters'''''
 SpatialParameters parameters = new SpatialParameters("MASK=ANYINTERACT QUERYTYPE=WINDOW");
 Expression selectionCriteria = 
           SpatialExpressionFactory.relate(expressionBuilder.get("geometry"),
                                           rectangle,
                                           parameters);


The following example demonstrates how to relate two expressions with <tt>SpatialParameters</tt> constructed using convenience methods.<br>


<span id="Example 108-2"></span>


''''' Relating Two Expressions'''''
 SpatialParameters parameters = new SpatialParameters();
 parameters.setQueryType(SpatialParameters.QueryType.WINDOW.setMask(Mask.ANYINTERACT);
 Expression selectionCriteria = 
           SpatialExpressionFactory.relate(expressionBuilder1.get("geometry"),
                                           expressionBuilder2.get("geometry"),
                                           parameters);



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