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package io.hypersistence.utils.hibernate.query;
import org.hibernate.HibernateException;
import org.hibernate.transform.ResultTransformer;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* The {@link MapResultTransformer} allows us to return
* a {@link Map} from a JPA {@link javax.persistence.Query}.
*
* If there are aliases named as {@code key} or {@code value},
* then those will be used.
*
* Otherwise, the first column value is the key while the second one is the Map value.
*
* For more details about how to use it, check out this article on vladmihalcea.com.
*
* @author Vlad Mihalcea
* @since 2.9.0
*/
public class MapResultTransformer implements ResultTransformer {
public static final String KEY_ALIAS = "map_key";
public static final String VALUE_ALIAS = "map_value";
private Map result = new HashMap<>();
/**
* Transform the tuple into a key/value pair.
*
* If there are aliases named as {@code key} or {@code value},
* then those will be used.
*
* Otherwise, the first column value is the key while the second one is the Map value.
*
* @param tuple tuple to be transformed to a key/value pair
* @param aliases column aliases
* @return unmodified tuple
*/
@Override
public Object transformTuple(Object[] tuple, String[] aliases) {
int keyOrdinal = -1;
int valueOrdinal = -1;
for (int i = 0; i < aliases.length; i++) {
String alias = aliases[i];
if (KEY_ALIAS.equalsIgnoreCase(alias)) {
keyOrdinal = i;
} else if (VALUE_ALIAS.equalsIgnoreCase(alias)) {
valueOrdinal = i;
}
}
if (keyOrdinal >= 0) {
if (valueOrdinal < 0) {
throw new HibernateException(
new IllegalArgumentException("A key column alias was given but no value column alias was found!")
);
}
} else {
if (valueOrdinal >= 0) {
throw new HibernateException(
new IllegalArgumentException("A value column alias was given but no key column alias was found!")
);
} else {
keyOrdinal = 0;
valueOrdinal = 1;
}
}
@SuppressWarnings("unchecked")
K key = (K) tuple[keyOrdinal];
@SuppressWarnings("unchecked")
V value = (V) tuple[valueOrdinal];
result.put(key, value);
return tuple;
}
/**
* Return the {@link Map} instead of the default {@link List}.
*
* @param tuples tuples
* @return the {@link Map} result set
*/
@Override
public List transformList(List tuples) {
return Collections.singletonList(result);
}
}