org.apache.metamodel

Class QueryPostprocessDataContext

java.lang.Object

org.apache.metamodel.AbstractDataContext

org.apache.metamodel.QueryPostprocessDataContext

All Implemented Interfaces:

HasReadTypeConverters, DataContext

Direct Known Subclasses:

CassandraDataContext, CouchDbDataContext, CsvDataContext, ElasticSearchDataContext, ExcelDataContext, FixedWidthDataContext, HBaseDataContext, JsonDataContext, MongoDbDataContext, PojoDataContext, QueryPostprocessDelegate, SalesforceDataContext, SugarCrmDataContext, XmlDomDataContext, XmlSaxDataContext

public abstract class QueryPostprocessDataContext
extends AbstractDataContext
implements HasReadTypeConverters

Abstract DataContext for data sources that do not support SQL queries natively. Instead this superclass only requires that a subclass can materialize a single table at a time. Then the query will be executed by post processing the datasets client-side.

Field Summary

Fields

Modifier and Type	Field and Description
static String	INFORMATION_SCHEMA_NAME

Constructor Summary

Constructors

Constructor and Description
QueryPostprocessDataContext()

Method Summary

Methods

Modifier and Type	Method and Description
void	addConverter(Column column, TypeConverter<?,?> converter) Adds a TypeConverter to this DataContext's query engine (Query Postprocessor) for read operations.
protected Number	executeCountQuery(Table table, List<FilterItem> whereItems, boolean functionApproximationAllowed) Executes a simple count query, if possible.
protected Row	executePrimaryKeyLookupQuery(Table table, List<SelectItem> selectItems, Column primaryKeyColumn, Object keyValue) Executes a query which obtains a row by primary key (as defined by Column.isPrimaryKey()).
DataSet	executeQuery(Query query) Executes a query against the DataContext.
protected String	getDefaultSchemaName() Gets the name of the default schema.
protected abstract Schema	getMainSchema()
protected Schema	getMainSchemaInternal() Deprecated. use AbstractDataContext.getDefaultSchema() instead
protected abstract String	getMainSchemaName()
protected Schema	getSchemaByNameInternal(String name) Gets a specific schema from the non-abstract implementation.
protected String[]	getSchemaNamesInternal() Gets schema names from the non-abstract implementation.
protected boolean	isMainSchemaTable(Table table)
protected boolean	isScalarFunctionMaterialized(ScalarFunction function) Determines if the subclass of this class can materialize SelectItems with the given ScalarFunction.
protected DataSet	materializeFromItem(FromItem fromItem, List<SelectItem> selectItems)
protected abstract DataSet	materializeMainSchemaTable(Table table, Column[] columns, int maxRows) Executes a simple one-table query against a table in the main schema of the subclasses of this class.
protected DataSet	materializeMainSchemaTable(Table table, Column[] columns, int firstRow, int maxRows) Executes a simple one-table query against a table in the main schema of the subclasses of this class.
protected DataSet	materializeMainSchemaTable(Table table, List<SelectItem> selectItems, int firstRow, int maxRows) Executes a simple one-table query against a table in the main schema of the subclasses of this class.
protected DataSet	materializeMainSchemaTable(Table table, List<SelectItem> selectItems, List<FilterItem> whereItems, int firstRow, int maxRows) Execute a simple one-table query against a table in the main schema of the subclasses of this class.
protected DataSet	materializeTable(Table table, List<SelectItem> selectItems, int firstRow, int maxRows) Deprecated.
protected DataSet	materializeTable(Table table, List<SelectItem> selectItems, List<FilterItem> whereItems, int firstRow, int maxRows)

Methods inherited from class org.apache.metamodel.AbstractDataContext

compileQuery, executeQuery, executeQuery, getColumnByQualifiedLabel, getDefaultSchema, getSchemaByName, getSchemaNames, getSchemas, getTableByQualifiedLabel, isQualifiedPathDelim, onSchemaCacheRefreshed, parseQuery, query, refreshSchemas

Methods inherited from class java.lang.Object

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

Field Detail

INFORMATION_SCHEMA_NAME

public static final String INFORMATION_SCHEMA_NAME

See Also:

Constant Field Values

Constructor Detail

QueryPostprocessDataContext

public QueryPostprocessDataContext()

Method Detail

executeQuery

public DataSet executeQuery(Query query)

Description copied from interface: DataContext

Executes a query against the DataContext.

Specified by:

executeQuery in interface DataContext

Parameters:

query - the query object to execute

Returns:

the DataSet produced from executing the query

executeCountQuery

protected Number executeCountQuery(Table table,
                       List<FilterItem> whereItems,
                       boolean functionApproximationAllowed)

Executes a simple count query, if possible. This method is provided to allow subclasses to optimize count queries since they are quite common and often a datastore can retrieve the count using some specialized means which is much more performant than counting all records manually.

Parameters:

table - the table on which the count is requested.

whereItems - a (sometimes empty) list of WHERE items.

functionApproximationAllowed - whether approximation is allowed or not.

Returns:

the count of the particular table, or null if not available.

executePrimaryKeyLookupQuery

protected Row executePrimaryKeyLookupQuery(Table table,
                               List<SelectItem> selectItems,
                               Column primaryKeyColumn,
                               Object keyValue)

Executes a query which obtains a row by primary key (as defined by Column.isPrimaryKey()). This method is provided to allow subclasses to optimize lookup queries since they are quite common and often a datastore can retrieve the row using some specialized means which is much more performant than scanning all records manually.

Parameters:

table - the table on which the lookup is requested.

selectItems - the items to select from the lookup query.

primaryKeyColumn - the column that is the primary key

keyValue - the primary key value that is specified in the lookup query.

Returns:

the row if the particular table, or null if not available.

materializeFromItem

protected DataSet materializeFromItem(FromItem fromItem,
                          List<SelectItem> selectItems)

materializeTable

protected DataSet materializeTable(Table table,
                       List<SelectItem> selectItems,
                       List<FilterItem> whereItems,
                       int firstRow,
                       int maxRows)

isScalarFunctionMaterialized

protected boolean isScalarFunctionMaterialized(ScalarFunction function)

Determines if the subclass of this class can materialize SelectItems with the given ScalarFunction. Usually scalar functions are applied by MetaModel on the client side, but when possible they can also be handled by e.g. materializeMainSchemaTable(Table, List, int, int) and materializeMainSchemaTable(Table, List, List, int, int) in which case MetaModel will not evaluate it client-side.

Parameters:

function -

Returns:

materializeTable

@Deprecated
protected DataSet materializeTable(Table table,
                                  List<SelectItem> selectItems,
                                  int firstRow,
                                  int maxRows)

Deprecated.

isMainSchemaTable

protected boolean isMainSchemaTable(Table table)

getSchemaNamesInternal

protected final String[] getSchemaNamesInternal()
                                         throws MetaModelException

Description copied from class: AbstractDataContext

Gets schema names from the non-abstract implementation. These schema names will be cached except if the AbstractDataContext.refreshSchemas() method is called.

Specified by:

getSchemaNamesInternal in class AbstractDataContext

Returns:

an array of schema names.

Throws:

MetaModelException

getDefaultSchemaName

protected String getDefaultSchemaName()
                               throws MetaModelException

Description copied from class: AbstractDataContext

Gets the name of the default schema.

Specified by:

getDefaultSchemaName in class AbstractDataContext

Returns:

the default schema name.

Throws:

MetaModelException

getSchemaByNameInternal

protected final Schema getSchemaByNameInternal(String name)
                                        throws MetaModelException

Description copied from class: AbstractDataContext

Gets a specific schema from the non-abstract implementation. This schema object will be cached except if the AbstractDataContext.refreshSchemas() method is called.

Specified by:

getSchemaByNameInternal in class AbstractDataContext

Parameters:

name - the name of the schema to get

Returns:

a schema object representing the named schema, or null if no such schema exists.

Throws:

MetaModelException

getMainSchemaInternal

@Deprecated
protected Schema getMainSchemaInternal()

Deprecated. use AbstractDataContext.getDefaultSchema() instead

Returns:

addConverter

public void addConverter(Column column,
                TypeConverter<?,?> converter)

Adds a TypeConverter to this DataContext's query engine (Query Postprocessor) for read operations. Note that this method should NOT be invoked directly by consuming code. Rather use Converters.addTypeConverter(DataContext, Column, TypeConverter) to ensure conversion on both reads and writes.

Specified by:

addConverter in interface HasReadTypeConverters

getMainSchema

protected abstract Schema getMainSchema()
                                 throws MetaModelException

Returns:

the main schema that subclasses of this class produce

Throws:

MetaModelException

getMainSchemaName

protected abstract String getMainSchemaName()
                                     throws MetaModelException

Returns:

the name of the main schema that subclasses of this class produce

Throws:

MetaModelException

materializeMainSchemaTable

protected DataSet materializeMainSchemaTable(Table table,
                                 List<SelectItem> selectItems,
                                 List<FilterItem> whereItems,
                                 int firstRow,
                                 int maxRows)

Execute a simple one-table query against a table in the main schema of the subclasses of this class. This default implementation will delegate to materializeMainSchemaTable(Table, List, int, int) and apply WHERE item filtering afterwards.

Parameters:

table -

selectItems -

whereItems -

firstRow -

maxRows -

Returns:

materializeMainSchemaTable

protected DataSet materializeMainSchemaTable(Table table,
                                 List<SelectItem> selectItems,
                                 int firstRow,
                                 int maxRows)

Executes a simple one-table query against a table in the main schema of the subclasses of this class. This default implementation will delegate to materializeMainSchemaTable(Table, Column[], int, int).

Parameters:

table -

selectItems -

firstRow -

maxRows -

Returns:

materializeMainSchemaTable

protected DataSet materializeMainSchemaTable(Table table,
                                 Column[] columns,
                                 int firstRow,
                                 int maxRows)

Executes a simple one-table query against a table in the main schema of the subclasses of this class. This default implementation will delegate to materializeMainSchemaTable(Table, Column[], int) and apply a FirstRowDataSet if necessary.

Parameters:

table -

columns -

firstRow -

maxRows -

Returns:

materializeMainSchemaTable

protected abstract DataSet materializeMainSchemaTable(Table table,
                                 Column[] columns,
                                 int maxRows)

Executes a simple one-table query against a table in the main schema of the subclasses of this class.

Parameters:

table - the table to query

columns - the columns of the table to query

maxRows - the maximum amount of rows needed or -1 if all rows are wanted.

Returns:

a dataset with the raw table/column content.