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Difference between revisions of "Introduction to EclipseLink Support for Oracle Spatial (ELUG)"

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To add your structure converter to the DatabasePlatform, 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]]).
 
To add your structure converter to the DatabasePlatform, 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]]).
 
 
 
  
  

Revision as of 11:13, 17 December 2007

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 (MDSYS.SDO_GEOMETRY).

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


EclipseLink Support for Oracle Spatial

EclipseLink provides support for direct mappings of database columns of type MDSYS.SDO_GEOMETRY to attributes of the oracle.spatial.geometry.JGeometry data type. Because this conversion requires an active JDBC connection, perform the conversion in the database platform (see Database Platforms) during retrieval from the JDBC result set. Then you must convert into a STRUCT type (for writing back into a SQL statement).

Consider the following:

  • You cannot express the JGeometry data type using literal SQL–always convert it to a STRUCT type, and then bind.
  • The object-relational data type structure mapping (see Object-Relational Data Type Structure Mapping) enables EclipseLink to build a Java object from the returned STRUCT type–instead, allow JGeometry to perform the conversion.

EclipseLink also provides support for spatial operators (see How to Perform Queries Using Spatial Operator Expressions) through the EclipseLink expression framework (see Introduction to EclipseLink Expressions), as well as for custom object types that wrap SDO_GEOMETRY.

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 org.eclipse.persistence.platform.database.DatabasePlatform (see Database Platforms) stores a list of structure converters.

To create a custom converter, implement the org.eclipse.persistence.platform.database.converters.StructConverter interface and register it on your direct-to-field mapping (see Direct-to-Field Mapping).

To use the StructConverter, do the following:

  1. Configure the database platform (see How to Configure the Database Platform to Use Structure Convertes).
  2. Set up a mapping (see How to Set Up Mappings Using Structure Converters).


How to Configure the Database Platform to Use Structure Convertes

EclipseLink uses a database platform (see 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 DatabasePlatform, call addStructConverter(StructConverter converter) method of the DatabasePlatform. Call this method within your EclipseLink session (server or database) prior to the session login (see Configuring a Session Login).


How to Set Up Mappings Using Structure Converters

Use direct-to-field mappings (see Direct-to-Field Mapping) to map your STRUCT types. For each mapping that maps to the type defined by the structure converter, set its field type to the STRUCT data type, as follows:

mapping.setFieldType(java.sql.Types.STRUCT);

Using JGeometry

To use the oracle.spatial.geometry.JGeometry, do the following:

  1. Configure the database platform (see How to Configure the Database Platform to Use JGeometry).
  2. Set up a mapping (see How to Map JGeometry Attributes).

You can query your mapped entities with expressions that use Spatial operators. For more information, see ow 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 oracle.toplink.platform.database.oracle.converters.JGeometryConverter as follows:

databasePlatform.addStructConverter(new JGeometryConverter());

You must configure this platform within your EclipseLink session prior to the session login (see Configuring a Session Login).


How to Map JGeometry Attributes

Use direct-to-field mappings (see Direct-to-Field Mapping) to map your STRUCT types. For each mapping that maps to the type defined by the structure converter (JGeometry), set its field type to the STRUCT 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 JGeometry attributes mapped to SDO_GEOMETRY columns. With this support, you can query for these mapped entities with native SQL queries using Oracle Spatial operators (see http://download-west.oracle.com/docs/cd/B19306_01/appdev.102/b14255/sdo_operat.htm#i76448).

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.

In its oracle.toplink.expressions.spatial package, EclipseLink provides the expression support for the following Spatial operators:

  • SDO_WITHIN_DISTANCE
  • SDO_RELATE
  • SDO_FILTER
  • SDO_NN

Use the following methods of the oracle.toplink.expressions.spatial.SpatialExpressionFactory class to build expressions that use Spatial operators:

  • withinDistance
  • relate
  • filter
  • nearestNeighbor

All these methods have the following common set of parameters:

  1. an expression (oracle.toplink.expressions.Expression) that points to JGeometry;
  2. JGeometry object or an Expression;
  3. an oracle.toplink.expressions.spatial.SpatialParameters object that defines the parameters to the function call.

The SpatialParameters class provides convenience methods that let you set the parameters representing the following:

  • minimum resolution;
  • maximum resolution;
  • units;
  • distance;
  • query type;
  • masks;
  • String of parameters.


This example demonstrates how to construct a Spatial operator expression, and then relate it to an existing JGeometry with SpatialParameters created using a String. 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);


This example demonstrates how to relate two expressions with SpatialParameters constructed using convenience methods. 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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