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

Latest revision as of 11:16, 23 July 2012

For the latest EclipseLink documentation, please see http://www.eclipse.org/eclipselink/documentation/

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.

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 using EclipseLink structure converter with application servers (for example, Oracle WebLogic Server, JBoss, 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 Converters

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 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 org.eclipse.persistence.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.

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 http://download.oracle.com/docs/cd/B28359_01/appdev.111/b28401/toc.htm.

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 org.eclipse.persistence.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 (org.eclipse.persistence.expressions.Expression) that points to JGeometry;
2. JGeometry object or an Expression;
3. an org.eclipse.persistence.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.

The following 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);

The following 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);

Using Nearest Neighbor

SpatialParameters parameters = new SpatialParameters();
parameters.setParams("sdo_num_res=10");
Expression expression = SpatialExpressionFactory.nearestNeighbor(expressionBuilder.get("geometry"), geom, parameters);

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