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https://issues.apache.org/jira/browse/METAMODEL-18?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14156738#comment-14156738
]
ASF GitHub Bot commented on METAMODEL-18:
-----------------------------------------
Github user kaspersorensen commented on a diff in the pull request:
https://github.com/apache/incubator-metamodel/pull/2#discussion_r18351203
--- Diff:
cassandra/src/main/java/org/apache/metamodel/cassandra/CassandraDataContext.java
---
@@ -0,0 +1,205 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.metamodel.cassandra;
+
+import com.datastax.driver.core.*;
+import com.datastax.driver.core.querybuilder.QueryBuilder;
+import com.datastax.driver.core.querybuilder.Select;
+
+import org.apache.metamodel.DataContext;
+import org.apache.metamodel.MetaModelException;
+import org.apache.metamodel.QueryPostprocessDataContext;
+import org.apache.metamodel.data.DataSet;
+import org.apache.metamodel.query.FilterItem;
+import org.apache.metamodel.schema.*;
+import org.apache.metamodel.util.SimpleTableDef;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * 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 {@link SimpleTableDef} class.
+ *
+ * @author Alberto Rodriguez
+ */
+public class CassandraDataContext extends QueryPostprocessDataContext
implements DataContext {
+
+ private static final Logger logger =
LoggerFactory.getLogger(CassandraDataContext.class);
+
+ private final Cluster cassandraCluster;
+ private final SimpleTableDef[] tableDefs;
+ private final String keySpaceName;
+
+ /**
+ * Constructs a {@link CassandraDataContext}. This constructor accepts
a
+ * custom array of {@link SimpleTableDef}s which allows the user to
define
+ * his own view on the indexes in the engine.
+ *
+ * @param cluster
+ * the Cassandra cluster
+ * @param keySpace
+ * the name of the Cassandra keyspace
+ * @param tableDefs
+ * an array of {@link SimpleTableDef}s, which define the
table
+ * and column model of the ElasticSearch index.
+ */
+ public CassandraDataContext(Cluster cluster, String keySpace,
SimpleTableDef... tableDefs) {
+ this.cassandraCluster = cluster;
+ this.keySpaceName = keySpace;
+ this.tableDefs = tableDefs;
+ }
+
+ /**
+ * Constructs a {@link CassandraDataContext} and automatically detects
+ * the schema structure/view on the keyspace (see
+ * {@link #detectSchema(Cluster, String)}).
+ *
+ * @param cluster
+ * the Cassandra cluster
+ * @param keySpace
+ * the name of the Cassandra keyspace to represent
+ */
+ public CassandraDataContext(Cluster cluster, String keySpace) {
+ this(cluster, keySpace, detectSchema(cluster, keySpace));
+ }
+
+ /**
+ * Performs an analysis of the given keyspace in a Cassandra cluster
+ * {@link Cluster} instance and detects the cassandra types structure
+ * based on the metadata provided by the datastax cassandra java
client.
+ *
+ * @see #detectTable(TableMetadata)
+ *
+ * @param cluster
+ * the cluster to inspect
+ * @param keyspaceName
+ * @return a mutable schema instance, useful for further fine tuning
by the
+ * user.
+ */
+ public static SimpleTableDef[] detectSchema(Cluster cluster, String
keyspaceName) {
+ Metadata metadata = cluster.getMetadata();
+ KeyspaceMetadata keyspace = metadata.getKeyspace(keyspaceName);
+ Collection<TableMetadata> tables = keyspace.getTables();
+ SimpleTableDef[] result = new SimpleTableDef[tables.size()];
+ int i = 0;
+ for (TableMetadata tableMetaData : tables) {
+ SimpleTableDef table = detectTable(tableMetaData);
+ result[i] = table;
+ i++;
+ }
+ return result;
+ }
+
+ /**
+ * Performs an analysis of an available table in Cassandra.
+ *
+ * @param tableMetaData
+ * the table meta data
+ * @return a table definition for cassandra.
+ */
+ public static SimpleTableDef detectTable(TableMetadata tableMetaData) {
+ List<ColumnMetadata> columns = tableMetaData.getColumns();
+ final String[] columnNames = new String[columns.size()];
+ final ColumnType[] columnTypes = new ColumnType[columns.size()];
+ int i = 0;
+ for (ColumnMetadata column: columns) {
+ columnNames[i] = column.getName();
+ columnTypes[i] =
getColumnTypeFromMetaDataField(column.getType().getName());
+ i++;
+ }
+
+ return new SimpleTableDef(tableMetaData.getName(), columnNames,
columnTypes);
+ }
+
+ @Override
+ protected Schema getMainSchema() throws MetaModelException {
+ final MutableSchema theSchema = new
MutableSchema(getMainSchemaName());
+ for (final SimpleTableDef tableDef : tableDefs) {
+ final MutableTable table =
tableDef.toTable().setSchema(theSchema);
+ theSchema.addTable(table);
+ }
+ return theSchema;
+ }
+
+
+ @Override
+ protected String getMainSchemaName() throws MetaModelException {
+ return keySpaceName;
+ }
+
+ @Override
+ protected DataSet materializeMainSchemaTable(Table table, Column[]
columns, int maxRows) {
+ Select query = QueryBuilder.select().all().from(keySpaceName,
table.getName());
+ if (limitMaxRowsIsSet(maxRows)) {
+ query.limit(maxRows);
+ }
+ final Iterator<Row> response =
cassandraCluster.connect().execute(query).iterator();
+ return new CassandraDataSet(response, columns, false);
+ }
+
+ private boolean limitMaxRowsIsSet(int maxRows) {
+ return (maxRows != -1);
+ }
+
+
+ @Override
+ protected Number executeCountQuery(Table table, List<FilterItem>
whereItems, boolean functionApproximationAllowed) {
+ if (!whereItems.isEmpty()) {
+ // not supported - will have to be done by counting client-side
+ return null;
+ }
+ Statement statement =
QueryBuilder.select().countAll().from(keySpaceName, table.getName());
+ final Row response =
cassandraCluster.connect().execute(statement).one();
+ return response.getLong(0);
+ }
+
+
+ private static ColumnType getColumnTypeFromMetaDataField(DataType.Name
metaDataName) {
+ switch (metaDataName) {
+ case BIGINT: return ColumnType.BIGINT;
+ case BLOB: return ColumnType.BLOB;
+ case BOOLEAN: return ColumnType.BOOLEAN;
+ case DECIMAL: return ColumnType.DECIMAL;
+ case DOUBLE: return ColumnType.DOUBLE;
+ case FLOAT: return ColumnType.FLOAT;
+ case INT: return ColumnType.INTEGER;
+ case TEXT: return ColumnType.STRING;
+ case TIMESTAMP: return ColumnType.TIMESTAMP;
+ case UUID: return ColumnType.STRING;
--- End diff --
This line is what I am referring to in the previous comment.
> Cassandra DB support for MetaModel
> ----------------------------------
>
> Key: METAMODEL-18
> URL: https://issues.apache.org/jira/browse/METAMODEL-18
> Project: Metamodel
> Issue Type: New Feature
> Reporter: Kasper Sørensen
> Priority: Critical
>
> A new module for MetaModel, providing support for Cassandra.
> Note that Cassandra in many respects is similar to HBase, and we might run
> into some of the same issues. Check METAMODEL-13 for our HBase module JIRA
> issue.
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