/*
 * Copyright 2002-2018 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.jdbc.support;

import java.util.List;
import java.util.Map;

import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.lang.Nullable;

Interface for retrieving keys, typically used for auto-generated keys
as potentially returned by JDBC insert statements.
Implementations of this interface can hold any number of keys.
In the general case, the keys are returned as a List containing one Map
for each row of keys.
Most applications only use on key per row and process only one row at a time in an insert statement. In these cases, just call getKey to retrieve the key. The returned value is a Number here, which is the usual type for auto-generated keys. 
Author:
Thomas Risberg, Juergen Hoeller
See Also:
JdbcTemplate
SqlUpdate
Since:
1.1/**
 * Interface for retrieving keys, typically used for auto-generated keys
 * as potentially returned by JDBC insert statements.
 *
 * <p>Implementations of this interface can hold any number of keys.
 * In the general case, the keys are returned as a List containing one Map
 * for each row of keys.
 *
 * <p>Most applications only use on key per row and process only one row at a
 * time in an insert statement. In these cases, just call {@code getKey}
 * to retrieve the key. The returned value is a Number here, which is the
 * usual type for auto-generated keys.
 *
 * @author Thomas Risberg
 * @author Juergen Hoeller
 * @since 1.1
 * @see org.springframework.jdbc.core.JdbcTemplate
 * @see org.springframework.jdbc.object.SqlUpdate
 */
public interface KeyHolder {

	
Retrieve the first item from the first map, assuming that there is just
one item and just one map, and that the item is a number.
This is the typical case: a single, numeric generated key.
Keys are held in a List of Maps, where each item in the list represents
the keys for each row. If there are multiple columns, then the Map will have
multiple entries as well. If this method encounters multiple entries in
either the map or the list meaning that multiple keys were returned,
then an InvalidDataAccessApiUsageException is thrown.
Throws:
InvalidDataAccessApiUsageException – if multiple keys are encountered
Returns:
the generated key as a number/**
	 * Retrieve the first item from the first map, assuming that there is just
	 * one item and just one map, and that the item is a number.
	 * This is the typical case: a single, numeric generated key.
	 * <p>Keys are held in a List of Maps, where each item in the list represents
	 * the keys for each row. If there are multiple columns, then the Map will have
	 * multiple entries as well. If this method encounters multiple entries in
	 * either the map or the list meaning that multiple keys were returned,
	 * then an InvalidDataAccessApiUsageException is thrown.
	 * @return the generated key as a number
	 * @throws InvalidDataAccessApiUsageException if multiple keys are encountered
	 */
	@Nullable
	Number getKey() throws InvalidDataAccessApiUsageException;

	
Retrieve the first map of keys.
If there are multiple entries in the list (meaning that multiple rows
had keys returned), then an InvalidDataAccessApiUsageException is thrown.
Throws:
InvalidDataAccessApiUsageException – if keys for multiple rows are encountered
Returns:
the Map of generated keys for a single row/**
	 * Retrieve the first map of keys.
	 * <p>If there are multiple entries in the list (meaning that multiple rows
	 * had keys returned), then an InvalidDataAccessApiUsageException is thrown.
	 * @return the Map of generated keys for a single row
	 * @throws InvalidDataAccessApiUsageException if keys for multiple rows are encountered
	 */
	@Nullable
	Map<String, Object> getKeys() throws InvalidDataAccessApiUsageException;

	
Return a reference to the List that contains the keys.
Can be used for extracting keys for multiple rows (an unusual case),
and also for adding new maps of keys.
Returns:
the List for the generated keys, with each entry representing
an individual row through a Map of column names and key values/**
	 * Return a reference to the List that contains the keys.
	 * <p>Can be used for extracting keys for multiple rows (an unusual case),
	 * and also for adding new maps of keys.
	 * @return the List for the generated keys, with each entry representing
	 * an individual row through a Map of column names and key values
	 */
	List<Map<String, Object>> getKeyList();

}