Package org.geotools.jdbc

Class SQLDialect

  • Direct Known Subclasses:
    BasicSQLDialect, DB2SQLDialect, H2Dialect, MySQLDialect, PreparedStatementSQLDialect
    public abstract class SQLDialect
extends Object
    The driver used by JDBCDataStore to directly communicate with the database.

    This class encapsulates all the database specific operations that JDBCDataStore needs to function. It is implemented on a per-database basis.

    Type Mapping

    One of the jobs of a dialect is to map sql types to java types and vice versa. This abstract implementation provides default mappings for "primitive" java types. The following mappings are provided. A '*' denotes that the mapping is the default java to sql mapping as well.
    • VARCHAR -> String *
    • CHAR -> String
    • LONGVARCHAR -> String
    • BIT -> Boolean
    • BOOLEAN -> Boolean *
    • SMALLINT -> Short *
    • TINYINT -> Short
    • INTEGER -> Integer *
    • BIGINT -> Long *
    • REAL -> Float *
    • DOUBLE -> Double *
    • FLOAT -> Double
    • NUMERIC -> BigDecimal *
    • DECIMAL -> BigDecimal
    • DATE -> java.sql.Date *
    • TIME -> java.sql.Time *
    • TIMESTAMP -> java.sql.Timestmap *
    Subclasses should extend (not override) the following methods to configure the mappings:

    This class is intended to be stateless, therefore subclasses should not maintain any internal state. If for some reason a subclass must keep some state around (not recommended), it must ensure that the state is accessed in a thread safe manner.

    Author:
    Justin Deoliveira, The Open Planning Project

    • Field Detail

      • LOGGER

        protected static final Logger LOGGER

      • BASE_DBMS_CAPABILITIES

        public static FilterCapabilities BASE_DBMS_CAPABILITIES
        The basic filter capabilities all databases should have

      • UNWRAPPER_NOT_FOUND

        protected static final UnWrapper UNWRAPPER_NOT_FOUND
        Sentinel value used to mark that the unwrapper lookup happened already, and an unwrapper was not found

      • uwMap

        protected final Map<Class<? extends Connection>,​UnWrapper> uwMap
        Map of UnWrapper objects keyed by the class of Connection it is an unwrapper for. This avoids the overhead of searching the DataSourceFinder service registry at each unwrap.

      • dataStore

        protected JDBCDataStore dataStore
        The datastore using the dialect

    • Constructor Detail

      • SQLDialect

        protected SQLDialect​(JDBCDataStore dataStore)
        Creates the dialect.
        Parameters:
        dataStore - The dataStore using the dialect.

    • Method Detail

      • initializeConnection

        public void initializeConnection​(Connection cx)
                          throws SQLException
        Initializes a newly created database connection.

        Subclasses should override this method if there is some additional action that needs to be taken when a new connection to the database is created. The default implementation does nothing.

        Parameters:
        cx - The new database connection.
        Throws:
        SQLException

      • includeTable

        public boolean includeTable​(String schemaName,
                            String tableName,
                            Connection cx)
                     throws SQLException
        Determines if the specified table should be included in those published by the datastore.

        This method returns true if the table should be published as a feature type, otherwise it returns false. Subclasses should override this method, this default implementation returns true.

        A database connection is provided to the dialect but it should not be closed. However any statements objects or result sets that are instantiated from it must be closed.

        Parameters:
        schemaName - The schema of the table, might be null..
        tableName - The name of the table.
        cx - Database connection.
        Throws:
        SQLException

      • registerSqlTypeNameToClassMappings

        public void registerSqlTypeNameToClassMappings​(Map<String,​Class<?>> mappings)
        Registers the sql type name to java type mappings that the dialect uses when reading and writing objects to and from the database.

        Subclasses should extend (not override) this method to provide additional mappings, or to override mappings provided by this implementation. This implementation provides the following mappings:

      • getRestrictions

        public Filter getRestrictions​(ResultSet columnMetaData,
                              Connection cx)
                       throws SQLException
        Allows the dialect to setup restrictions for attribute at hand
        Parameters:
        columnMetaData - The column metadata
        cx - The connection used to retrieve the metadata
        Returns:
        The restriction, or null if no restriction applies
        Throws:
        SQLException

      • handleUserDefinedType

        public void handleUserDefinedType​(ResultSet columnMetaData,
                                  ColumnMetadata metadata,
                                  Connection cx)
                           throws SQLException
        Handles the mapping for a user defined type.

        This method is called after getMapping(ResultSet, Connection) but before the rest of the type mapping heuristics are applied.

        Implementing this method is optional. It is used to allow for handling user defined types or "DOMAINS". Dialects that implement this method should set the appropriate information on the metadata object to allow the column to be mapped via the regular type mapping heuristics.

        Parameters:
        columnMetaData - The column metdata.
        metadata - The column metadata object that collections mapping information.
        cx - The database connection, not to be closed.
        Throws:
        SQLException

      • registerSqlTypeToClassMappings

        public void registerSqlTypeToClassMappings​(Map<Integer,​Class<?>> mappings)
        Registers the sql type to java type mappings that the dialect uses when reading and writing objects to and from the database.

        Subclasses should extend (not override) this method to provide additional mappings, or to override mappings provided by this implementation. This implementation provides the following mappings:

      • registerClassToSqlMappings

        public void registerClassToSqlMappings​(Map<Class<?>,​Integer> mappings)
        Registers the java type to sql type mappings that the datastore uses when reading and writing objects to and from the database. *

        Subclasses should extend (not override) this method to provide additional mappings, or to override mappings provided by this implementation. This implementation provides the following mappings:

      • registerSqlTypeToSqlTypeNameOverrides

        public void registerSqlTypeToSqlTypeNameOverrides​(Map<Integer,​String> overrides)
        Registers any overrides that should occur when mapping an integer sql type value to an underlying sql type name.

        The default implementation of this method does nothing. Subclasses should override in cases where:

        • database type metadata does not provide enough information to properly map
        • to support custom types (those not in Types)

      • registerAggregateFunctions

        public void registerAggregateFunctions​(Map<Class<? extends FeatureVisitor>,​String> aggregates)
        Registers the set of aggregate functions the dialect is capable of handling.

        Aggregate functions are handled via visitors of special types. The aggregates maps the class of the visitor to the associated function name. This base implementation handles some of the well known mappings:

        Subclasses should extend (not override) to provide additional functions.

      • getNameEscape

        public String getNameEscape()
        Returns the string used to escape names.

        This value is used to escape any name in a query. This includes columns, tables, schemas, indexes, etc... If no escape is necessary this method should return the empty string, and never return null.

        This default implementation returns a single double quote ("), subclasses must override to provide a different espcape.

      • escapeName

        public String escapeName​(String name)
        Surrounds a name with the SQL escape string.

        If the name contains the SQL escape string, the SQL escape string is duplicated.

      • encodeColumnName

        public void encodeColumnName​(String prefix,
                             String raw,
                             StringBuffer sql)
        Encodes the name of a column in an SQL statement.

        This method escapes raw using method escapeName(String). Subclasses usually don't override this method and instead override getNameEscape().

        The prefix parameter may be null so subclasses that do override must handle that case.

      • encodeColumnType

        public void encodeColumnType​(String sqlTypeName,
                             StringBuffer sql)
        Encodes the type of a column in an SQL CREATE TABLE statement.

        The default implementation simply outputs the sqlTypeName argument as is. Subclasses may override this method. Such cases might include:

        • A type definition requires some parameter, ex: size of a varchar
        • The provided attribute (att) contains some additional restrictions that can be encoded in the type, ex: field length

      • encodeColumnAlias

        public void encodeColumnAlias​(String raw,
                              StringBuffer sql)
        Encodes the alias of a column in an sql query.

        This default implementation uses the syntax: 

        as "alias"
        . Subclasses should override to provide a different syntax.

      • encodeTableAlias

        public void encodeTableAlias​(String raw,
                             StringBuffer sql)
        Encodes the alias of a table in an sql query.

        This default implementation uses the syntax: 

        as "alias"
        . Subclasses should override to provide a different syntax.

      • encodeTableName

        public void encodeTableName​(String raw,
                            StringBuffer sql)
        Encodes the name of a table in an SQL statement.

        This method escapes raw using method escapeName(String). Subclasses usually dont override this method and instead override getNameEscape().

      • encodeSchemaName

        public void encodeSchemaName​(String raw,
                             StringBuffer sql)
        Encodes the name of a schema in an SQL statement.

        This method escapes raw using method escapeName(String). Subclasses usually dont override this method and instead override getNameEscape().

      • getGeometryTypeName

        public String getGeometryTypeName​(Integer type)
        Returns the name of a geometric type based on its integer constant.

        The constant, type, is registered in registerSqlTypeNameToClassMappings(Map).

        This default implementation returns null, subclasses should override.

      • getGeometrySRID

        public Integer getGeometrySRID​(String schemaName,
                               String tableName,
                               String columnName,
                               Connection cx)
                        throws SQLException
        Returns the spatial reference system identifier (srid) for a particular geometry column.

        This method is given a direct connection to the database. The connection must not be closed. However any statements or result sets instantiated from the connection must be closed.

        In the event that the srid cannot be determined, this method should return null .

        Parameters:
        schemaName - The database schema, could be null.
        tableName - The table, never null.
        columnName - The column name, never null
        cx - The database connection.
        Throws:
        SQLException

      • getGeometryDimension

        public int getGeometryDimension​(String schemaName,
                                String tableName,
                                String columnName,
                                Connection cx)
                         throws SQLException
        Returns the dimension of the coordinates in the geometry. Defaults to 2, subclasses can override it.

        This method is given a direct connection to the database. The connection must not be closed. However any statements or result sets instantiated from the connection must be closed.

        In the event that the dimension cannot be determined, this method should return 2

        Parameters:
        schemaName - The database schema, could be null.
        tableName - The table, never null.
        columnName - The column name, never null
        cx - The database connection.
        Throws:
        SQLException

      • createCRS

        public CoordinateReferenceSystem createCRS​(int srid,
                                           Connection cx)
                                    throws SQLException
        Turns the specified srid into a CoordinateReferenceSystem, or returns null if not possible.

        Note this implementation takes account of forceLongitudeFirst which should be set when longitude first (XY) axis ordering is required.

        The implementation might just use CRS.decode("EPSG:" + srid), but most spatial databases will have their own SRS database that can be queried as well.

        As a rule of thumb you should override this method if your spatial database uses codes that are not part of the EPSG standard database, of if for some reason you deem it preferable to use your database definition instead of an official EPSG one.

        Most overrides will try out to decode the official EPSG code first, and fall back on the custom database definition otherwise

        Throws:
        SQLException

      • getOptimizedBounds

        public List<ReferencedEnvelope> getOptimizedBounds​(String schema,
                                                   SimpleFeatureType featureType,
                                                   Connection cx)
                                            throws SQLException,
                                                   IOException
        Returns the bounds of all geometry columns in the layer using any approach that proves to be faster than the plain bounds aggregation (e.g., better than the "plain select extent(geom) from table" on PostGIS), or null if none exists or the fast method has not been enabled (e.g., if the fast method is just an estimate of the bounds you probably want the user to enable it manually)
        Parameters:
        schema - The database schema, if any, or null
        featureType - The feature type containing the geometry columns whose bounds need to computed. Mind, it may be retyped and thus contain less geometry columns than the table
        Returns:
        a list of referenced envelopes (some of which may be null or empty)
        Throws:
        SQLException
        IOException

      • encodeGeometryEnvelope

        public abstract void encodeGeometryEnvelope​(String tableName,
                                            String geometryColumn,
                                            StringBuffer sql)
        Encodes the spatial extent function of a geometry column in a SELECT statement.

        This method must also be sure to properly encode the name of the column with the #encodeColumnName(String, StringBuffer) function.

      • decodeGeometryEnvelope

        public abstract Envelope decodeGeometryEnvelope​(ResultSet rs,
                                                int column,
                                                Connection cx)
                                         throws SQLException,
                                                IOException
        Decodes the result of a spatial extent function in a SELECT statement.

        This method is given direct access to a result set. The column parameter is the index into the result set which contains the spatial extent value. The query for this value is build with the encodeGeometryEnvelope(String, String, StringBuffer) method.

        This method must not read any other objects from the result set other then the one referenced by column.

        Parameters:
        rs - A result set
        column - Index into the result set which points at the spatial extent value.
        cx - The database connection.
        Throws:
        SQLException
        IOException

      • encodeGeometryColumn

        public void encodeGeometryColumn​(GeometryDescriptor gatt,
                                 String prefix,
                                 int srid,
                                 Hints hints,
                                 StringBuffer sql)
        Encodes the name of a geometry column in a SELECT statement.

        This method should wrap the column name in any functions that are used to retrieve its value. For instance, often it is necessary to use the function asText, or asWKB when fetching a geometry.

        This method must also be sure to properly encode the name of the column with the encodeColumnName(String, String, StringBuffer) function.

        Example: 

           
   sql.append( "asText(" );
   column( gatt.getLocalName(), sql );
   sql.append( ")" );

      • decodeGeometryValue

        public abstract Geometry decodeGeometryValue​(GeometryDescriptor descriptor,
                                             ResultSet rs,
                                             String column,
                                             GeometryFactory factory,
                                             Connection cx,
                                             Hints hints)
                                      throws IOException,
                                             SQLException
        Decodes a geometry value from the result of a query.

        This method is given direct access to a result set. The column parameter is the index into the result set which contains the geometric value.

        An implementation should deserialize the value provided by the result set into Geometry object. For example, consider an implementation which deserializes from well known text: 

           String wkt = rs.getString( column );
   if ( wkt == null ) {
     return null;
   }
   return new WKTReader(factory).read( wkt );
        Note that implementations must handle null values.

        The factory parameter should be used to instantiate any geometry objects.

        Throws:
        IOException
        SQLException

      • encodePrimaryKey

        public void encodePrimaryKey​(String column,
                             StringBuffer sql)
        Encodes the primary key definition in a CREATE TABLE statement.

        Subclasses should override this method if need be, the default implementation does the following: 

           
   encodeColumnName( column, sql );
   sql.append( " int PRIMARY KEY" );

      • encodeJoin

        public void encodeJoin​(Join.Type joinType,
                       StringBuffer sql)
        Encodes the syntax for a join between two tables.

      • encodeCreateTable

        public void encodeCreateTable​(StringBuffer sql)
        Encodes the CREATE TABLE statement.

        Default implementation adds "CREATE TABLE" to the sql buffer. Subclasses may choose to override to handle db specific syntax.

      • encodePostColumnCreateTable

        public void encodePostColumnCreateTable​(AttributeDescriptor att,
                                        StringBuffer sql)
        Encodes anything post a column in a CREATE TABLE statement.

        This is appended after the column name and type. Subclasses may choose to override this method, the default implementation does nothing.

        Parameters:
        att - The attribute corresponding to the column.

      • encodePostCreateTable

        public void encodePostCreateTable​(String tableName,
                                  StringBuffer sql)
        Encodes anything post a CREATE TABLE statement.

        This is appended to a CREATE TABLE statement after the column definitions. This default implementation does nothing, subclasses should override as need be.

      • encodePostSelect

        public void encodePostSelect​(SimpleFeatureType featureType,
                             StringBuffer sql)
        Encodes anything after the SELECT clause and before the FROM clause.

        This method does not nothing, subclass may override to add additional columns.

        Parameters:
        featureType - The feature type being queried.

      • postCreateTable

        public void postCreateTable​(String schemaName,
                            SimpleFeatureType featureType,
                            Connection cx)
                     throws SQLException,
                            IOException
        Callback to execute any additional sql statements post a create table statement.

        This method should be implemented by subclasses that need to do some post processing on the database after a table has been created. Examples might include:

        • Creating a sequence for a primary key
        • Registering geometry column metadata
        • Creating a spatial index

        A common case is creating an auto incrementing sequence for the primary key of a table. It should be noted that all tables created through the datastore use the column "fid" as the primary key.

        A direct connection to the database is provided (cx). This connection must not be closed, however any statements or result sets instantiated from the connection must be closed.

        Parameters:
        schemaName - The name of the schema, may be null.
        featureType - The feature type that has just been created on the database.
        cx - Database connection.
        Throws:
        SQLException
        IOException

      • postCreateAttribute

        public void postCreateAttribute​(AttributeDescriptor att,
                                String tableName,
                                String schemaName,
                                Connection cx)
                         throws SQLException
        Callback which executes after an attribute descriptor has been built from a table column.

        The result set columnMetadata should not be modified in any way (including scrolling) , it should only be read from.

        This base implementation does nothing, subclasses should override as need be.

        Parameters:
        att - The built attribute descriptor.
        tableName - The name of the table containing the column
        schemaName - The name of the database scheam containing the table containing the column
        cx - The database connection.
        Throws:
        SQLException

      • postCreateFeatureType

        public void postCreateFeatureType​(SimpleFeatureType featureType,
                                  DatabaseMetaData metadata,
                                  String schemaName,
                                  Connection cx)
                           throws SQLException
        Callback which executes after a feature type has been built from a database table.

        This base implementation does nothing, subclasses should override as need be.

        Parameters:
        featureType - The build feature type.
        metadata - The database metadata.
        schemaName - The name of the database scheam containing the table containing the column
        cx - The database connection.
        Throws:
        SQLException

      • preDropTable

        public void preDropTable​(String schemaName,
                         SimpleFeatureType featureType,
                         Connection cx)
                  throws SQLException
        Callback which executes before a table is about to be dropped.

        This base implementation does nothing, subclasses should override as need be.

        Parameters:
        schemaName - The database schema containing the table.
        featureType - The featureType/table being dropped.
        cx - The database connection.
        Throws:
        SQLException

      • postDropTable

        public void postDropTable​(String schemaName,
                          SimpleFeatureType featureType,
                          Connection cx)
                   throws SQLException
        Callback which executes after a table has been dropped.

        This base implementation does nothing, subclasses should override as need be.

        Parameters:
        schemaName - The database schema containing the table.
        featureType - The featureType/table being dropped.
        cx - The database connection.
        Throws:
        SQLException

      • getNextAutoGeneratedValue

        public Object getNextAutoGeneratedValue​(String schemaName,
                                        String tableName,
                                        String columnName,
                                        Connection cx)
                                 throws SQLException
        Obtains the next value of an auto generated column.

        Implementations should determine the next value of a column for which values are automatically generated by the database.

        This method is given a direct connection to the database, but this connection should never be closed. However any statements or result sets instantiated from the connection must be closed.

        Implementations should handle the case where schemaName is null.

        Parameters:
        schemaName - The schema name, this might be null.
        tableName - The name of the table.
        columnName - The column.
        cx - The database connection.
        Returns:
        The next value of the column, or null.
        Throws:
        SQLException

      • getLastAutoGeneratedValue

        public Object getLastAutoGeneratedValue​(String schemaName,
                                        String tableName,
                                        String columnName,
                                        Connection cx,
                                        Statement st)
                                 throws SQLException
        Obtains the last value of an auto generated column.

        This method is only called when lookupGeneratedValuesPostInsert() returns true. Implementations should determine the previous value of a column for which was automatically generated by the database.

        This method is given a direct connection to the database, but this connection should never be closed. However any statements or result sets instantiated from the connection must be closed.

        Implementations should handle the case where schemaName is null.

        Parameters:
        schemaName - The schema name, this might be null.
        tableName - The name of the table.
        columnName - The column.
        cx - The database connection.
        st - The statement used for the insert
        Returns:
        The previous value of the column, or null.
        Throws:
        SQLException

      • getLastAutoGeneratedValue

        public Object getLastAutoGeneratedValue​(String schemaName,
                                        String tableName,
                                        String columnName,
                                        Connection cx)
                                 throws SQLException
        Obtains the last value of an auto generated column.

        This method is only called when lookupGeneratedValuesPostInsert() returns true. Implementations should determine the previous value of a column for which was automatically generated by the database.

        This method is given a direct connection to the database, but this connection should never be closed. However any statements or result sets instantiated from the connection must be closed.

        Implementations should handle the case where schemaName is null.

        Parameters:
        schemaName - The schema name, this might be null.
        tableName - The name of the table.
        columnName - The column.
        cx - The database connection.
        Returns:
        The previous value of the column, or null.
        Throws:
        SQLException

      • getSequenceForColumn

        public String getSequenceForColumn​(String schemaName,
                                   String tableName,
                                   String columnName,
                                   Connection cx)
                            throws SQLException
        Determines the name of the sequence (if any) which is used to increment generate values for a table column.

        This method should return null if no such sequence exists.

        This method is given a direct connection to the database, but this connection should never be closed. However any statements or result sets instantiated from the connection must be closed.

        Parameters:
        schemaName - The schema name, this might be null.
        tableName - The table name.
        columnName - The column name.
        cx - The database connection.
        Throws:
        SQLException

      • getNextSequenceValue

        public Object getNextSequenceValue​(String schemaName,
                                   String sequenceName,
                                   Connection cx)
                            throws SQLException
        Obtains the next value of a sequence, incrementing the sequence to the next state in the process.

        Implementations should determine the next value of a column for which values are automatically generated by the database.

        This method is given a direct connection to the database, but this connection should never be closed. However any statements or result sets instantiated from the connection must be closed.

        Implementations should handle the case where schemaName is null.

        Parameters:
        schemaName - The schema name, this might be null.
        sequenceName - The name of the sequence.
        cx - The database connection.
        Returns:
        The next value of the sequence, or null.
        Throws:
        SQLException

      • encodeNextSequenceValue

        public String encodeNextSequenceValue​(String schemaName,
                                      String sequenceName)
        Encodes how to get the next sequence value from the DB.

        Implementations should handle the case where schemaName is null.

      • isAggregatedSortSupported

        public boolean isAggregatedSortSupported​(String function)
        Returns true if this dialect supports sorting together with the given aggregation function.

      • isGroupBySupported

        public boolean isGroupBySupported()
        Returns true if this dialect supports group by clause.

      • applyLimitOffset

        public void applyLimitOffset​(StringBuffer sql,
                             int limit,
                             int offset)
        Alters the query provided so that limit and offset are natively dealt with. This might mean simply appending some extra directive to the query, or wrapping it into a bigger one.

      • getDefaultVarcharSize

        public int getDefaultVarcharSize()
        Determines the default length that a varchar field should be when creating datastore tables from feature types.

        Some dialects allow no length to be specified for varchar fields (PostGIS for example) however others require a maximum length to be set.

        Subclasses can override this method and either return -1 to specify that no length is required, or otherwise return an appropriate default length for varchars of that dialect.

      • isAutoCommitQuery

        public boolean isAutoCommitQuery()
        Determine if a read query should be set to autocommit.

        Some databases (like postgres) want this enabled to respect fetch size. The default implementation is to return false.

        Returns:
        true if read queries should remain autocommit, false otherwise

      • supportsSchemaForIndex

        protected boolean supportsSchemaForIndex()
        Return true if the database supports individual schemas for indices.

        The SQL encoding would be CREATE INDEX SCHEMANAME.INDEXNAME ON ....

        The default is false and the encoding is CREATE INDEX INDEXNAME ON ....

        Returns:
        true or false

      • createIndex

        public void createIndex​(Connection cx,
                        SimpleFeatureType schema,
                        String databaseSchema,
                        Index index)
                 throws SQLException
        Performs the class "create [unique] indexName on tableName(att1, att2, ..., attN)" call.

        Subclasses can override to handle special indexes (like spatial ones) and/or the hints

        Throws:
        SQLException

      • handleSelectHints

        public void handleSelectHints​(StringBuffer sql,
                              SimpleFeatureType featureType,
                              Query query)
        Used to apply search hints on the fully generated SQL (complete of select, from, where, sort, limit/offset)

      • applyHintsOnVirtualTables

        public boolean applyHintsOnVirtualTables()
        Controls whether select hints should be added to queries on virtual tables.
        Returns:
        True if select hints hould be added to queries on virtual tables, false otherwise.

      • getDesiredTablesType

        public String[] getDesiredTablesType()
        Returns:
        Table types filtered from jdbc DatabaseMetaData

      • splitFilter

        public Filter[] splitFilter​(Filter filter,
                            SimpleFeatureType schema)
        Splits the filter into two parts, an encodable one, and a non encodable one. The default implementation uses the filter capabilities to split the filter, subclasses can implement their own logic if need be.

      • canSimplifyPoints

        public boolean canSimplifyPoints()
        Returns if points can be returned in simplified form (e.g reduced precision, like TWKB encoding)

      • getResultTypes

        protected Optional<List<Class>> getResultTypes​(FeatureVisitor visitor,
                                               SimpleFeatureType featureType)
        Returns the list of aggregation output types for the given visitor and feature type (or an empty Optional if could not determine it)

      • getAggregateConverter

        public Function<Object,​Object> getAggregateConverter​(FeatureVisitor visitor,
                                                           SimpleFeatureType featureType)
        Returns a converter used to transform the results of an aggregation, for the given visitor and feature type. The default implementation returns an identify function, databases with type system limitations can use it to convert the result to the desired type. Implementations overriding this method might use getResultTypes(FeatureVisitor, SimpleFeatureType) to compute the expected result type of the aggregation expressions.
        Parameters:
        visitor -
        featureType -
        Returns:

      • getSQLType

        public Integer getSQLType​(AttributeDescriptor ad)
        Gives an opportunity to the dialect to do its own custom type mapping, based on the full description of the attribute. Defaults to return null, subclasses can override
        Parameters:
        ad - The attribute descriptor
        Returns:
        A SQL type from Types, or null if customization is needed

      • convertValue

        public Object convertValue​(Object value,
                           AttributeDescriptor ad)
        Convertes the given value to the target type. The default implementation uses converters to match the attribute descriptor binding, subclasses can override.

      • canGroupOnGeometry

        public boolean canGroupOnGeometry()
        Returns true if this database can "group by" on a Geometry column. Defaults to false, specific implementations with this capability should override

      • getMapping

        public Class<?> getMapping​(String sqlTypeName)
        Returns the java type mapped to the a specified sql type name defined by the dialect.

        If there is no such type mapped to sqlTypeName, null is returned.

        Parameters:
        sqlTypeName - The name of the sql type.
        Returns:
        The mapped java class, or null. if no such mapping exists.