com.luciad.format.sqlite.spatialite

LuciadFusionClass TLcdSpatiaLiteModelDecoder

java.lang.Object

com.luciad.format.sqlite.spatialite.TLcdSpatiaLiteModelDecoder

All Implemented Interfaces:

ILcdModelDecoder

@LcdService(service=ILcdModelDecoder.class,
            priority=20000)
public class TLcdSpatiaLiteModelDecoder
extends Object
implements ILcdModelDecoder

This model decoder decodes spatial tables from SQLite SpatiaLite databases.

Input files

File	Required	Entry point	Description
*.spl		x	Java properties file containing all the necessary properties to access the spatial data

Alternatively, a Properties object can be constructed programmatically and passed to the model decoder.

The common properties needed to establish a connection are:

• driver (default = org.sqlite.JDBC): the JDBC driver that will be used to connect to the database.
• url: the database URL, absolute or relative to the location of the properties file.

Other JDBC properties that can help to tune the database connection are passed on to JDBC as well.

The properties that identify the tables, columns, rows, etc. within the database are:

• table: the name of the table containing the geometries. The table name may be qualified by prepending the database schema. It may be followed by one or more spaces and an alias, which can be used instead of the original name to disambiguate columns in the other properties.
• spatialColumn: the column containing the geometries.
• spatialQueryColumn: an optional column containing the geometries that should be used in spatial queries. By default, this column is equal to the spatialColumn. It should not be changed for most typical applications.
• featureNames.0, ...: the column names that should be retrieved as object features in the model. For read-only models, more complex SQL expressions, or columns from selection tables (see below) are accepted too.
• featureDisplayNames.0, ...: optional display names corresponding to the feature names.
• primaryFeatureIndex (default = 0): the index of the feature that serves as a primary key.
• primaryFeatureAutoGenerated (default = false): specifies whether the database automatically generates the primary key whenever a geometry is inserted into the spatial table. The primary feature on the java side will then be updated with this generated value.
• selectionTables (default = null): an optional comma-separated list of tables required to constrain the geometries of the model. These tables will be added after the main table in the FROM parts of SELECT queries. A name may be followed by one or more spaces and an alias, which can be used instead of the original name to disambiguate columns in the other properties.
• selectionFilter (default = null): an optional SQL select query to constrain the geometries of the model. This query will be added after the spatial query in the WHERE parts of SELECT queries.

If a schema name, table name, or spatial column name is surrounded by double quotes (") then the quotes are stripped and the remaining string is passed unmodified to SQLite. If a name is not quoted, then it is converted to lower case before being passed on to the database. See the SQLite documentation for a more detailed explanation. A schema name may be quoted separately from the actual table name.

Supported file transfer protocols

• This model decoder supports all transfer protocols that are supported by java.io.File.

Model structure

• This model decoder creates a model per spatial table.
• The models returned by this decoder are instances of TLcdDatabaseModel or TLcdDatabaseReadOnlyModel, depending on whether this decoder creates read-only models or not.
• All models returned by this model decoder implement ILcd2DBoundsIndexedModel.

Model descriptor

• The model descriptor of a decoded model is a TLcdSpatiaLiteModelDescriptor.

Three optional properties allow to override some metadata in the model descriptor:

• sourceName (default = the source name that is passed to the model decoder): the source name of the model descriptor.
• typeName (default = the display name of the model decoder): the type name of the model descriptor. The type name is also used when composing the name of the data model.
• displayName (default = the spatial table name): the display name of the model descriptor. The display name is also used when composing the name of the data model and the name of the data type.

Model reference

By default, the model reference of a decoded model is determined by the EPSG code or the WKT reference of the spatial table. If no model reference can be created the default model reference set on this decoder will be used (see setDefaultModelReference(com.luciad.model.ILcdModelReference)).

Model elements

• A decoded database model contains ILcdShape objects, decoded from the Well-Known Binary representation that SpatiaLite provides:

  FROM WKB GEOMETRY	TO ILcdShape
  POINT	ILcdShapeList with an ILcd2DEditablePoint object
  LINESTRING	ILcdShapeList with an ILcd2DEditablePolyline object
  POLYGON	ILcdShapeList with an ILcdComplexPolygon object
  MULTIPOINT	ILcdShapeList with an ILcd2DEditablePolypoint object
  MULTILINESTRING	ILcdShapeList with ILcd2DEditablePolyline objects
  MULTIPOLYGON	ILcdShapeList with ILcdComplexPolygon objects
  GEOMETRYCOLLECTION	ILcdShapeList with objects from this table (also recursive)

• The elements also implement the ILcdFeatured interface and the ILcdDataObject interface, providing access to their features.
• Instead of static typing, sqlite uses manifest typing, i.e. the datatype is a property of the value itself, not a column property. Sqlite allows to store any datatype in any column. As a result all the element's properties are of type TLcdCoreDataTypes.OBJECT_TYPE.

Useful settings

• The decoder property readOnly can be set to specify whether the model will be used as a read-only model.

Sample code

Decoding SQLite data and visualizing it on a Lightspeed map:

    //First create the model
    ILcdModelDecoder decoder =
        new TLcdCompositeModelDecoder(TLcdServiceLoader.getInstance(ILcdModelDecoder.class));
    ILcdModel model = decoder.decode("Data/Sqlite/states.spl");

    //Create a layer for the model with default styling
    ILspLayer layer = TLspShapeLayerBuilder.newBuilder()
                                           .model(model)
                                           .build();

    //Add the layer to the Lightspeed view (an ILspView)
    view.addLayer(layer);

Decoding SQLite data and visualizing it on a GXY map:

    //First create the model
    ILcdModelDecoder decoder =
        new TLcdCompositeModelDecoder(TLcdServiceLoader.getInstance(ILcdModelDecoder.class));
    ILcdModel model = decoder.decode("Data/Sqlite/states.spl");

    //Create a layer for the model with default styling
    ILcdGXYLayer layer = TLcdGXYLayer.create(model);
    //Wrap the layer with an async layer wrapper to ensure
    //that the view remains responsive while data is being painted
    layer = ILcdGXYAsynchronousLayerWrapper.create(layer);

    //Add the async layer to the GXY view (an ILcdGXYView)
    view.addGXYLayer(layer);

An example of the states.spl file is available in the samples.

Performance tips

Some optional properties in the properties file or object can help to tune the database access:

• alwaysCloseConnection (default = false): an optional boolean to specify that the database connection should be closed after each query.
• maxCacheSize (default = 100, or the value set on the decoder): the maximum number of objects in the cache. Using a cache will improve performance if transferring and decoding geometries and their features is relatively expensive compared to performing the original SQL queries. The current implementation of the decoder will then perform queries in two passes, first retrieving the relevant primary keys and then retrieving and decoding the actual geometries and features that are not in the cache. On the other hand, setting the cache size to 0 may be better if performing SQL queries is relatively expensive. The current implementation of the decoder will then perform queries in a single pass, retrieving and decoding the relevant geometries every time.

Thread safety

• The decoding of models is thread-safe, as long as no properties are changed during the decoding.
• The decoded models are thread-safe for read access.

Supported versions and specifications

• SQLite SpatiaLite files, up to version 3.x of SpatiaLite.

Known limitations

• Some rare EPSG and WKT model references are not supported.
• Updating database views and data sets involving additional tables is generally not possible.
• The decoder does not respect the user's schema search path when decoding some GIS-specific metadata (srid and geometry type). If you have tables/columns with identical names but under different schemas it is therefore possible that a wrong model reference might be used. To avoid this problem it is recommended that you specify the table name as a qualified name (including the schema).

Since:

11.0

Constructor Summary

Constructors

Constructor and Description
TLcdSpatiaLiteModelDecoder() Creates a new, read-write SQLite SpatiaLite model decoder.
TLcdSpatiaLiteModelDecoder(boolean aReadOnly) Creates a new SQLite SpatiaLite model decoder.

Method Summary

Modifier and Type	Method and Description
boolean	canDecodeSource(String aSourceAsString) Checks whether this model decoder can decode the specified data source.
ILcdModel	decode(Properties aProperties) Decodes a new database model based on the given properties.
ILcdModel	decode(String aSourceName) Decodes a new database model based on the properties specified in the given file.
int	getDefaultMaxCacheSize() Return the default maximum size of the cache, expressed in number of elements (rows|geometries).
ILcdModelReference	getDefaultModelReference() Returns the default model reference to be assigned to decoded models.
String	getDisplayName() Returns a short, displayable name for the format that is decoded by this ILcdModelDecoder.
boolean	getReadOnly()
void	setDefaultMaxCacheSize(int aDefaultMaxCacheSize) Sets the default maximum size of the cache.
void	setDefaultModelReference(ILcdModelReference aDefaultModelReference) Sets the default model reference to be assigned to decoded models if no model reference can be created based on information from the database.
void	setReadOnly(boolean aReadOnly) Specifies whether the decoded models should be read-only or not.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.luciad.model.ILcdModelDecoder

canDecodeSource, decodeModelMetadata, decodeModelMetadata, decodeSource, discoverDataSources

Constructor Detail

TLcdSpatiaLiteModelDecoder

public TLcdSpatiaLiteModelDecoder()

Creates a new, read-write SQLite SpatiaLite model decoder.

TLcdSpatiaLiteModelDecoder

public TLcdSpatiaLiteModelDecoder(boolean aReadOnly)

Creates a new SQLite SpatiaLite model decoder.

Parameters:

aReadOnly - specifies the type of models the decoder should construct.

Method Detail

setDefaultModelReference

public void setDefaultModelReference(ILcdModelReference aDefaultModelReference)

Sets the default model reference to be assigned to decoded models if no model reference can be created based on information from the database.

Parameters:

aDefaultModelReference - the default model reference.

See Also:

getDefaultModelReference()

getDefaultModelReference

public ILcdModelReference getDefaultModelReference()

Returns the default model reference to be assigned to decoded models.

Returns:

the default model reference.

See Also:

setDefaultModelReference(com.luciad.model.ILcdModelReference)

setDefaultMaxCacheSize

public void setDefaultMaxCacheSize(int aDefaultMaxCacheSize)

Sets the default maximum size of the cache. It is possible to override this value by means of the maxCacheSize property in the properties file.

Parameters:

aDefaultMaxCacheSize - the default maximum number of objects in the cache.

getDefaultMaxCacheSize

public int getDefaultMaxCacheSize()

Return the default maximum size of the cache, expressed in number of elements (rows|geometries).

setReadOnly

public void setReadOnly(boolean aReadOnly)

Specifies whether the decoded models should be read-only or not.

Parameters:

aReadOnly - specifies the type of models the decoder should construct. If true, the decoder will create TLcdDatabaseReadOnlyModel objects. If false, the decoder will create TLcdDatabaseModel objects.

getReadOnly

public boolean getReadOnly()

See Also:

setReadOnly()

getDisplayName

public String getDisplayName()

Description copied from interface: ILcdModelDecoder

Returns a short, displayable name for the format that is decoded by this ILcdModelDecoder.

Specified by:

getDisplayName in interface ILcdModelDecoder

Returns:

the displayable name of this ILcdModelDecoder.

canDecodeSource

public boolean canDecodeSource(String aSourceAsString)

Description copied from interface: ILcdModelDecoder

Checks whether this model decoder can decode the specified data source. It is acceptable for this method to return true for a source name while decode throws an exception for that same source name.

For performance reasons, we strongly recommend that this will only be a simple test. For example: check the file extension of a file, but not that the file exists or contains expected content.

Specified by:

canDecodeSource in interface ILcdModelDecoder

Parameters:

aSourceAsString - the data source to be verified; typically a file name or a URL.

Returns:

true if this decoder can likely decode the data specified by the source name, false otherwise.

See Also:

ILcdModelDecoder.decode(String), ILcdModelDecoder.decodeModelMetadata(String)

decode

public ILcdModel decode(String aSourceName)
                 throws IOException

Decodes a new database model based on the properties specified in the given file.

Specified by:

decode in interface ILcdModelDecoder

Parameters:

aSourceName - the data source to be decoded; typically a file name or a URL.

Returns:

A model containing the decoded data. While null is allowed, implementors are advised to throw an error instead.

Throws:

IOException - for any exceptions caused by IO problems or invalid data. Since decoding invalid data almost always results in RunTimeExceptions (NullPointerException, IndexOutOfBoundsException, IllegalArgumentException, ...) on unexpected places, implementations are advised to catch RuntimeExceptions in their decode() method, and wrap them into an IOException, as illustrated in the code snippet below.

   public ILcdModel decode( String aSourceName ) throws IOException {
      try (InputStream input = fInputStreamFactory.createInputStream(aSourceName)) {
         // Perform decoding ...
      } catch (RuntimeException e) {
         throw new IOException(e);
      }
   }
 

InterruptedIOException - When the thread on which this method is called is interrupted: it is recommended to stop the decoding and throw an InterruptedIOException. This same exception can also be used if the decoder shows UI to the user, and the user cancels the decoding through the UI.

See Also:

ILcdModelDecoder.canDecodeSource(String)

decode

public ILcdModel decode(Properties aProperties)
                 throws IOException

Decodes a new database model based on the given properties.

Throws:

IOException