org.apache.metamodel.cassandra

Class CassandraDataContext

java.lang.Object

org.apache.metamodel.AbstractDataContext

org.apache.metamodel.QueryPostprocessDataContext

org.apache.metamodel.cassandra.CassandraDataContext

All Implemented Interfaces:

HasReadTypeConverters, DataContext

public class CassandraDataContext
extends QueryPostprocessDataContext
implements DataContext

DataContext implementation for Apache Cassandra database. When instantiating this DataContext, a keyspace name is provided. In Cassandra, the keyspace is the container for your application data, similar to a schema in a relational database. Keyspaces are used to group column families together. This implementation supports either automatic discovery of a schema or manual specification of a schema, through the SimpleTableDef class.

Field Summary

Fields inherited from class org.apache.metamodel.QueryPostprocessDataContext

INFORMATION_SCHEMA_NAME

Constructor Summary

Constructors

Constructor and Description
CassandraDataContext(com.datastax.driver.core.Cluster cluster, String keySpace) Constructs a CassandraDataContext and automatically detects the schema structure/view on the keyspace (see detectSchema(Cluster, String)).
CassandraDataContext(com.datastax.driver.core.Cluster cluster, String keySpace, SimpleTableDef... tableDefs) Constructs a CassandraDataContext.

Method Summary

Modifier and Type	Method and Description
static SimpleTableDef[]	detectSchema(com.datastax.driver.core.Cluster cluster, String keyspaceName) Performs an analysis of the given keyspace in a Cassandra cluster Cluster instance and detects the cassandra types structure based on the metadata provided by the datastax cassandra java client.
static SimpleTableDef	detectTable(com.datastax.driver.core.TableMetadata tableMetaData) Performs an analysis of an available table in Cassandra.
protected Number	executeCountQuery(Table table, List<FilterItem> whereItems, boolean functionApproximationAllowed) Executes a simple count query, if possible.
protected Schema	getMainSchema()
protected String	getMainSchemaName()
protected 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.

Methods inherited from class org.apache.metamodel.QueryPostprocessDataContext

addConverter, executePrimaryKeyLookupQuery, executeQuery, getDefaultSchemaName, getMainSchemaInternal, getSchemaByNameInternal, getSchemaNamesInternal, isMainSchemaTable, isScalarFunctionMaterialized, materializeFromItem, materializeMainSchemaTable, materializeMainSchemaTable, materializeMainSchemaTable, materializeTable, materializeTable

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

Methods inherited from interface org.apache.metamodel.DataContext

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

Constructor Detail

CassandraDataContext

public CassandraDataContext(com.datastax.driver.core.Cluster cluster,
                            String keySpace,
                            SimpleTableDef... tableDefs)

Constructs a CassandraDataContext. This constructor accepts a custom array of SimpleTableDefs which allows the user to define his own view on the indexes in the engine.

Parameters:

cluster - the Cassandra cluster

keySpace - the name of the Cassandra keyspace

tableDefs - an array of SimpleTableDefs, which define the table and column model of the ElasticSearch index.

CassandraDataContext

public CassandraDataContext(com.datastax.driver.core.Cluster cluster,
                            String keySpace)

Constructs a CassandraDataContext and automatically detects the schema structure/view on the keyspace (see detectSchema(Cluster, String)).

Parameters:

cluster - the Cassandra cluster

keySpace - the name of the Cassandra keyspace to represent

Method Detail

detectSchema

public static SimpleTableDef[] detectSchema(com.datastax.driver.core.Cluster cluster,
                                            String keyspaceName)

Performs an analysis of the given keyspace in a Cassandra cluster Cluster instance and detects the cassandra types structure based on the metadata provided by the datastax cassandra java client.

Parameters:

cluster - the cluster to inspect

keyspaceName -

Returns:

a mutable schema instance, useful for further fine tuning by the user.

See Also:

detectTable(TableMetadata)

detectTable

public static SimpleTableDef detectTable(com.datastax.driver.core.TableMetadata tableMetaData)

Performs an analysis of an available table in Cassandra.

Parameters:

tableMetaData - the table meta data

Returns:

a table definition for cassandra.

getMainSchema

protected Schema getMainSchema()
                        throws MetaModelException

Specified by:

getMainSchema in class QueryPostprocessDataContext

Returns:

the main schema that subclasses of this class produce

Throws:

MetaModelException

getMainSchemaName

protected String getMainSchemaName()
                            throws MetaModelException

Specified by:

getMainSchemaName in class QueryPostprocessDataContext

Returns:

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

Throws:

MetaModelException

materializeMainSchemaTable

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

Description copied from class: QueryPostprocessDataContext

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

Specified by:

materializeMainSchemaTable in class QueryPostprocessDataContext

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.

executeCountQuery

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

Description copied from class: QueryPostprocessDataContext

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.

Overrides:

executeCountQuery in class QueryPostprocessDataContext

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.