net.java.ao.schema.OnUpdate Maven / Gradle / Ivy
/*
* Copyright 2007 Daniel Spiewak
*
* 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 net.java.ao.schema;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Specifies a value for the field to receive in the event of an UPDATE
* or INSERT statement in some other field of the corresponding row. This
* is most often used to implement a modified field, as it does
* not require manual re-specification of the update value in every place
* an UPDATE is performed.
*
* The functionality of this annotation is modeled after the MySQL
* ON UPDATE field clause. However, because no other databases
* implement a similar syntax, triggers are often used as the implementation
* mechanism. Ironically, this means that most databases have a more
* flexible implementation of the functionality than MySQL. ActiveObjects
* performs no intrinsic checking to enforce limitations on the annotation's
* usage (for example, MySQL requires only one field with DEFAULT or
* ON UPDATE value equaling CURRENT_TIMESTAMP). This sort of checking is
* left entirely up to the database against which the migration is running.
*
* Currently, this annotation is unsupported on HSQLDB due to the way it
* handles triggers. However, there is no hard limit actually preventing
* the functionality.
*
* This annotation is only relevant to migrations. It has no effect upon
* "runtime" entity usage.
*
* @author Daniel Spiewak
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface OnUpdate {
/**
* Contains the database-agnostic representation of the default value
* for the corresponding field. The conversion between this
* String and the appropriate value is handled by the
* {@link net.java.ao.types.DatabaseType#defaultParseValue(String)}
* method. Thus, even default values for custom types are supported.
*/
String value();
}