/*
* Copyright 2017 the original author or authors.
*
* 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 org.springframework.cassandra.core.converter;
import java.util.List;
import java.util.Map;
import org.springframework.core.convert.converter.Converter;
import com.datastax.driver.core.ResultSet;
/**
* Convenient converter that can be used to convert a single-row-single-column, single-row-multi-column, or multi-row
* {@link ResultSet} into the a value of a given type. The majority of the expected usage is to convert a
* single-row-single-column result set into the target type.
* <p/>
* The algorithm is:
* <ul>
* <li>if there is one row with one column, convert that value to this converter's type if possible or throw,</li>
* <li>else if there is one row with multiple columns, convert the columns into this converter's type if possible or
* throw,</li>
* <li>else convert the rows into this converter's type (since there are multiple rows) or throw.</li>
* </ul>
* <p/>
* If the converter throws due to the inability to convert a given {@link ResultSet}, it will throw an
* {@link IllegalArgumentException}.
*
* @author Matthew T. Adams
* @author Mark Paluch
* @param <T>
*/
public abstract class AbstractResultSetConverter<T> implements Converter<ResultSet, T> {
private static final ResultSetToListConverter converter = new ResultSetToListConverter();
/**
* Converts the given value to this converter's type or throws {@link IllegalArgumentException}.
*/
protected abstract T doConvertSingleValue(Object object);
/**
* @return the target type.
*/
protected abstract Class<?> getType();
/**
* @return surrogate value if the {@link ResultSet} is {@literal null}.
*/
protected T getNullResultSetValue() {
return null;
}
/**
* @return surrogate value if the {@link ResultSet} is {@link ResultSet#isExhausted() exhausted}.
*/
protected T getExhaustedResultSetValue() {
return null;
}
@Override
public T convert(ResultSet source) {
if (source == null) {
return getNullResultSetValue();
}
if (source.isExhausted()) {
return getExhaustedResultSetValue();
}
List<Map<String, Object>> list = converter.convert(source);
if (list.size() == 1) {
Map<String, Object> map = list.get(0);
return map.size() == 1 ? doConvertSingleValue(map.get(map.keySet().iterator().next())) : doConvertSingleRow(map);
}
return doConvertResultSet(list);
}
/**
* Converts the given result set (as a {@link List}<{@link Map}<String,Object>>) to this converter's type
* or throws {@link IllegalArgumentException}. This default implementation simply throws.
*/
protected T doConvertResultSet(List<Map<String, Object>> resultSet) {
doThrow("result set");
return null;
}
/**
* Converts the given row (as a {@link Map}<String,Object>) to this converter's type or throws
* {@link IllegalArgumentException}. This default implementation simply throws.
*/
protected T doConvertSingleRow(Map<String, Object> row) {
doThrow("row");
return null;
}
void doThrow(String string) {
throw new IllegalArgumentException(
String.format("Cannot convert %s to desired type [%s]", string, getType().getName()));
}
}