package com.google.code.morphia.annotations;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* <p>Annotation which helps migrate schemas by loading one of several possible properties
* in the document into fields or methods. This is typically used when a field is renamed,
* allowing the field to be populated by both its current name and any prior names.</p>
*
* <ul>
* <li>When placed on a field, the additional names (document field) will be checked
* when this field is loaded. If the document contains data for more than one of the names,
* an exception will be thrown.
* <li>When placed on a parameter to a method that takes a single parameter, the method
* will be called with the data value. As with fields, any ambiguity in the data (multiple
* properties that would cause the method to be called) will produce an exception. However,
* {@code @AlsoLoad} on a method parameter *can* be used to override field names and "steal" the
* value that would otherwise have been set on a field. This can be useful when changing the
* type of a field.</li>
* </ul>
*
* (orig @author Jeff Schnitzer <jeff@infohazard.org> for Objectify)
* @author Scott Hernandez
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
public @interface AlsoLoad
{
String[] value();
}
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