org.apache.metamodel

Class MetaModelHelper

java.lang.Object

org.apache.metamodel.MetaModelHelper

public final class MetaModelHelper
extends Object

This class contains various helper functionality to common tasks in MetaModel, eg.:

• Easy-access for traversing common schema items
• Manipulate data in memory. These methods are primarily used to enable queries for non-queryable data sources like CSV files and spreadsheets.
• Query rewriting, traversing and manipulation.

The class is mainly intended for internal use within the framework operations, but is kept stable, so it can also be used by framework users.

Method Summary

Methods

Modifier and Type	Method and Description
static SelectItem[]	createSelectItems(Column... columns)
static Row	executeSingleRowQuery(DataContext dataContext, Query query) Executes a single row query, like "SELECT COUNT(*), MAX(SOME_COLUMN) FROM MY_TABLE" or similar.
static DataSet	getAggregated(List<SelectItem> workSelectItems, DataSet dataSet) Applies aggregate values to a dataset.
static DataSet	getCarthesianProduct(DataSet... fromDataSets)
static DataSet	getCarthesianProduct(DataSet[] fromDataSets, FilterItem... filterItems)
static DataSet	getCarthesianProduct(DataSet[] fromDataSets, Iterable<FilterItem> whereItems)
static Column[]	getColumnsBySuperType(Column[] columns, SuperColumnType superColumnType)
static Column[]	getColumnsByType(Column[] columns, ColumnType columnType)
static DataSet	getDistinct(DataSet dataSet)
static DataSet	getFiltered(DataSet dataSet, FilterItem... filterItems)
static DataSet	getFiltered(DataSet dataSet, Iterable<FilterItem> filterItems)
static List<SelectItem>	getFunctionSelectItems(Iterable<SelectItem> selectItems)
static DataSet	getGrouped(List<SelectItem> selectItems, DataSet dataSet, Collection<GroupByItem> groupByItems)
static DataSet	getGrouped(List<SelectItem> selectItems, DataSet dataSet, GroupByItem[] groupByItems)
static DataSet	getLeftJoin(DataSet ds1, DataSet ds2, FilterItem[] onConditions) Performs a left join (aka left outer join) operation on two datasets.
static DataSet	getOrdered(DataSet dataSet, List<OrderByItem> orderByItems)
static DataSet	getOrdered(DataSet dataSet, OrderByItem... orderByItems)
static DataSet	getRightJoin(DataSet ds1, DataSet ds2, FilterItem[] onConditions) Performs a right join (aka right outer join) operation on two datasets.
static DataSet	getSelection(List<SelectItem> selectItems, DataSet dataSet)
static DataSet	getSelection(SelectItem[] selectItems, DataSet dataSet)
static Column[]	getTableColumns(Table table, Column[] columns) Creates a subset array of columns, where only columns that are contained within the specified table are included.
static Column[]	getTableColumns(Table table, Iterable<Column> columns) Creates a subset array of columns, where only columns that are contained within the specified table are included.
static List<FromItem>	getTableFromItems(FromItem item)
static FromItem[]	getTableFromItems(Query q) Examines a query and extracts an array of FromItem's that refer (directly) to tables (hence Joined FromItems and SubQuery FromItems are traversed but not included).
static Table[]	getTables(Collection<Table> tableList, Iterable<Column> columnList) Creates an array of tables where all occurences of tables in the provided list of tables and columns are included
static Table[]	getTables(Column[] columns)
static Table[]	getTables(Iterable<Column> columns) Converts a list of columns to a corresponding array of tables
static boolean	isInformationSchema(Schema schema) Determines if a schema is an information schema
static boolean	isInformationSchema(String name) Determines if a schema name is the name of an information schema
static Query	parseQuery(DataContext dc, String queryString)
static List<Row>	readDataSetFull(DataSet dataSet)

Methods inherited from class java.lang.Object

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

Method Detail

getTables

public static Table[] getTables(Collection<Table> tableList,
                Iterable<Column> columnList)

Creates an array of tables where all occurences of tables in the provided list of tables and columns are included

isInformationSchema

public static boolean isInformationSchema(Schema schema)

Determines if a schema is an information schema

Parameters:

schema -

Returns:

isInformationSchema

public static boolean isInformationSchema(String name)

Determines if a schema name is the name of an information schema

Parameters:

name -

Returns:

getTables

public static Table[] getTables(Iterable<Column> columns)

Converts a list of columns to a corresponding array of tables

Parameters:

columns - the columns that the tables will be extracted from

Returns:

an array containing the tables of the provided columns.

getTableColumns

public static Column[] getTableColumns(Table table,
                       Iterable<Column> columns)

Creates a subset array of columns, where only columns that are contained within the specified table are included.

Parameters:

table -

columns -

Returns:

an array containing the columns that exist in the table

getTableColumns

public static Column[] getTableColumns(Table table,
                       Column[] columns)

Creates a subset array of columns, where only columns that are contained within the specified table are included.

Parameters:

table -

columns -

Returns:

an array containing the columns that exist in the table

getCarthesianProduct

public static DataSet getCarthesianProduct(DataSet... fromDataSets)

getCarthesianProduct

public static DataSet getCarthesianProduct(DataSet[] fromDataSets,
                           Iterable<FilterItem> whereItems)

getCarthesianProduct

public static DataSet getCarthesianProduct(DataSet[] fromDataSets,
                           FilterItem... filterItems)

getFiltered

public static DataSet getFiltered(DataSet dataSet,
                  Iterable<FilterItem> filterItems)

getFiltered

public static DataSet getFiltered(DataSet dataSet,
                  FilterItem... filterItems)

getSelection

public static DataSet getSelection(List<SelectItem> selectItems,
                   DataSet dataSet)

getSelection

public static DataSet getSelection(SelectItem[] selectItems,
                   DataSet dataSet)

getGrouped

public static DataSet getGrouped(List<SelectItem> selectItems,
                 DataSet dataSet,
                 Collection<GroupByItem> groupByItems)

getGrouped

public static DataSet getGrouped(List<SelectItem> selectItems,
                 DataSet dataSet,
                 GroupByItem[] groupByItems)

getAggregated

public static DataSet getAggregated(List<SelectItem> workSelectItems,
                    DataSet dataSet)

Applies aggregate values to a dataset. This method is to be invoked AFTER any filters have been applied.

Parameters:

workSelectItems - all select items included in the processing of the query (including those originating from other clauses than the SELECT clause).

dataSet -

Returns:

getFunctionSelectItems

public static List<SelectItem> getFunctionSelectItems(Iterable<SelectItem> selectItems)

getOrdered

public static DataSet getOrdered(DataSet dataSet,
                 List<OrderByItem> orderByItems)

getOrdered

public static DataSet getOrdered(DataSet dataSet,
                 OrderByItem... orderByItems)

readDataSetFull

public static List<Row> readDataSetFull(DataSet dataSet)

getTableFromItems

public static FromItem[] getTableFromItems(Query q)

Examines a query and extracts an array of FromItem's that refer (directly) to tables (hence Joined FromItems and SubQuery FromItems are traversed but not included).

Parameters:

q - the query to examine

Returns:

an array of FromItem's that refer directly to tables

getTableFromItems

public static List<FromItem> getTableFromItems(FromItem item)

executeSingleRowQuery

public static Row executeSingleRowQuery(DataContext dataContext,
                        Query query)
                                 throws MetaModelException

Executes a single row query, like "SELECT COUNT(*), MAX(SOME_COLUMN) FROM MY_TABLE" or similar.

Parameters:

dataContext - the DataContext object to use for executing the query

query - the query to execute

Returns:

a row object representing the single row returned from the query

Throws:

MetaModelException - if less or more than one Row is returned from the query

getLeftJoin

public static DataSet getLeftJoin(DataSet ds1,
                  DataSet ds2,
                  FilterItem[] onConditions)

Performs a left join (aka left outer join) operation on two datasets.

Parameters:

ds1 - the left dataset

ds2 - the right dataset

onConditions - the conditions to join by

Returns:

the left joined result dataset

getRightJoin

public static DataSet getRightJoin(DataSet ds1,
                   DataSet ds2,
                   FilterItem[] onConditions)

Performs a right join (aka right outer join) operation on two datasets.

Parameters:

ds1 - the left dataset

ds2 - the right dataset

onConditions - the conditions to join by

Returns:

the right joined result dataset

createSelectItems

public static SelectItem[] createSelectItems(Column... columns)

getDistinct

public static DataSet getDistinct(DataSet dataSet)

getTables

public static Table[] getTables(Column[] columns)

getColumnsByType

public static Column[] getColumnsByType(Column[] columns,
                        ColumnType columnType)

getColumnsBySuperType

public static Column[] getColumnsBySuperType(Column[] columns,
                             SuperColumnType superColumnType)

parseQuery

public static Query parseQuery(DataContext dc,
               String queryString)