DropColumnTask.java

/*
 * Licensed 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 com.facebook.presto.execution;

import com.facebook.presto.Session;
import com.facebook.presto.common.QualifiedObjectName;
import com.facebook.presto.metadata.Metadata;
import com.facebook.presto.spi.ColumnHandle;
import com.facebook.presto.spi.MaterializedViewDefinition;
import com.facebook.presto.spi.TableHandle;
import com.facebook.presto.spi.WarningCollector;
import com.facebook.presto.spi.security.AccessControl;
import com.facebook.presto.sql.analyzer.SemanticException;
import com.facebook.presto.sql.tree.DropColumn;
import com.facebook.presto.sql.tree.Expression;
import com.facebook.presto.sql.tree.Identifier;
import com.facebook.presto.transaction.TransactionManager;
import com.google.common.util.concurrent.ListenableFuture;

import java.util.List;
import java.util.Optional;

import static com.facebook.presto.metadata.MetadataUtil.createQualifiedObjectName;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.MISSING_COLUMN;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.MISSING_TABLE;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.NOT_SUPPORTED;
import static com.google.common.util.concurrent.Futures.immediateFuture;

public class DropColumnTask
        implements DDLDefinitionTask<DropColumn>
{
    @Override
    public String getName()
    {
        return "DROP COLUMN";
    }

    @Override
    public ListenableFuture<?> execute(DropColumn statement, TransactionManager transactionManager, Metadata metadata, AccessControl accessControl, Session session, List<Expression> parameters, WarningCollector warningCollector, String query)
    {
        QualifiedObjectName tableName = createQualifiedObjectName(session, statement, statement.getTable(), metadata);
        Optional<TableHandle> tableHandleOptional = metadata.getMetadataResolver(session).getTableHandle(tableName);

        if (!tableHandleOptional.isPresent()) {
            if (!statement.isTableExists()) {
                throw new SemanticException(MISSING_TABLE, statement, "Table '%s' does not exist", tableName);
            }
            return immediateFuture(null);
        }

        Optional<MaterializedViewDefinition> optionalMaterializedView = metadata.getMetadataResolver(session).getMaterializedView(tableName);
        if (optionalMaterializedView.isPresent()) {
            if (!statement.isTableExists()) {
                throw new SemanticException(NOT_SUPPORTED, statement, "'%s' is a materialized view, and drop column is not supported", tableName);
            }
            return immediateFuture(null);
        }

        TableHandle tableHandle = tableHandleOptional.get();
        Identifier columnIdentifier = statement.getColumn();
        String column = metadata.normalizeIdentifier(session, tableName.getCatalogName(), columnIdentifier.getValue());

        accessControl.checkCanDropColumn(session.getRequiredTransactionId(), session.getIdentity(), session.getAccessControlContext(), tableName);

        ColumnHandle columnHandle = metadata.getColumnHandles(session, tableHandle).get(column);
        if (columnHandle == null) {
            if (!statement.isColumnExists()) {
                throw new SemanticException(MISSING_COLUMN, statement, "Column '%s' does not exist", column);
            }
            return immediateFuture(null);
        }

        if (metadata.getColumnMetadata(session, tableHandle, columnHandle).isHidden()) {
            throw new SemanticException(NOT_SUPPORTED, statement, "Cannot drop hidden column");
        }

        if (metadata.getTableMetadata(session, tableHandle).getColumns().stream()
                .filter(info -> !info.isHidden()).count() <= 1) {
            throw new SemanticException(NOT_SUPPORTED, statement, "Cannot drop the only column in a table");
        }

        metadata.dropColumn(session, tableHandle, columnHandle);

        return immediateFuture(null);
    }
}