/*
 * Copyright 2014-2020 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
 *
 *      https://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.data.mapping;

import org.springframework.lang.Nullable;

Interface for a component allowing the access of identifier values.
Author:
Oliver Gierke, Mark Paluch
See Also:
TargetAwareIdentifierAccessor/**
 * Interface for a component allowing the access of identifier values.
 *
 * @author Oliver Gierke
 * @author Mark Paluch
 * @see TargetAwareIdentifierAccessor
 */
public interface IdentifierAccessor {

	
Returns the value of the identifier.
Returns:
the identifier of the underlying instance./**
	 * Returns the value of the identifier.
	 *
	 * @return the identifier of the underlying instance.
	 */
	@Nullable
	Object getIdentifier();

	
Returns the identifier of the underlying instance. Implementations are strongly recommended to extends either TargetAwareIdentifierAccessor or override this method to add more context to the exception being thrown in case of the absence of an identifier. 
Throws:
IllegalStateException – in case no identifier could be retrieved.
Returns:
the identifier of the underlying instance
Since:
2.0/**
	 * Returns the identifier of the underlying instance. Implementations are strongly recommended to extends either
	 * {@link TargetAwareIdentifierAccessor} or override this method to add more context to the exception being thrown in
	 * case of the absence of an identifier.
	 *
	 * @return the identifier of the underlying instance
	 * @throws IllegalStateException in case no identifier could be retrieved.
	 * @since 2.0
	 */
	default Object getRequiredIdentifier() {

		Object identifier = getIdentifier();

		if (identifier != null) {
			return identifier;
		}

		throw new IllegalStateException("Could not obtain identifier!");
	}
}