1/*- 2 * See the file LICENSE for redistribution information. 3 * 4 * Copyright (c) 2002,2008 Oracle. All rights reserved. 5 * 6 * $Id: SecondaryKey.java,v 1.1 2008/02/07 17:12:28 mark Exp $ 7 */ 8 9package com.sleepycat.persist.model; 10 11import static java.lang.annotation.ElementType.FIELD; 12import static java.lang.annotation.RetentionPolicy.RUNTIME; 13 14import java.lang.annotation.Documented; 15import java.lang.annotation.Retention; 16import java.lang.annotation.Target; 17 18import com.sleepycat.db.DatabaseException; 19import com.sleepycat.persist.PrimaryIndex; 20import com.sleepycat.persist.SecondaryIndex; // for javadoc 21import com.sleepycat.persist.StoreConfig; 22 23/** 24 * Indicates a secondary key field of an entity class. The value of the 25 * secondary key field is a unique or non-unique identifier for the entity and 26 * is accessed via a {@link SecondaryIndex}. 27 * 28 * <p>{@code SecondaryKey} may appear on any number of fields in an entity 29 * class, subclasses and superclasses. For a secondary key field in the entity 30 * class or one of its superclasses, all entity instances will be indexed by 31 * that field (if it is non-null). For a secondary key field in an entity 32 * subclass, only instances of that subclass will be indexed by that field (if 33 * it is non-null).</p> 34 * 35 * <p>If a secondary key field is null, the entity will not be indexed by that 36 * key. In other words, the entity cannot be queried by that secondary key nor 37 * can the entity be found by iterating through the secondary index.</p> 38 * 39 * <p>For a given entity class and its superclasses and subclasses, no two 40 * secondary keys may have the same name. By default, the field name 41 * identifies the secondary key and the secondary index for a given entity 42 * class. {@link #name} may be specified to override this default.</p> 43 * 44 * <p>Using {@link #relate}, instances of the entity class are related to 45 * secondary keys in a many-to-one, one-to-many, many-to-many, or one-to-one 46 * relationship. This required property specifies the <em>cardinality</em> of 47 * each side of the relationship.</p> 48 * 49 * <p>A secondary key may optionally be used to form a relationship with 50 * instances of another entity class using {@link #relatedEntity} and {@link 51 * #onRelatedEntityDelete}. This establishes <em>foreign key constraints</em> 52 * for the secondary key.</p> 53 * 54 * <p>The secondary key field type must be an array or collection type when a 55 * <em>x-to-many</em> relationship is used or a singular type when an 56 * <em>x-to-one</em> relationship is used; see {@link #relate}.</p> 57 * 58 * <p>The field type (or element type, when an array or collection type is 59 * used) of a secondary key field must follow the same rules as for a {@link 60 * <a href="PrimaryKey.html#keyTypes">primary key type</a>}. The {@link <a 61 * href="PrimaryKey.html#sortOrder">key sort order</a>} is also the same.</p> 62 * 63 * @author Mark Hayes 64 */ 65@Documented @Retention(RUNTIME) @Target(FIELD) 66public @interface SecondaryKey { 67 68 /** 69 * Defines the relationship between instances of the entity class and the 70 * secondary keys. 71 * 72 * <p>The table below summarizes how to create all four variations of 73 * relationships.</p> 74 * <div> 75 * <table border="yes"> 76 * <tr><th>Relationship</th> 77 * <th>Field type</th> 78 * <th>Key type</th> 79 * <th>Example</th> 80 * </tr> 81 * <tr><td>{@link Relationship#ONE_TO_ONE}</td> 82 * <td>Singular</td> 83 * <td>Unique</td> 84 * <td>A person record with a unique social security number 85 * key.</td> 86 * </tr> 87 * <tr><td>{@link Relationship#MANY_TO_ONE}</td> 88 * <td>Singular</td> 89 * <td>Duplicates</td> 90 * <td>A person record with a non-unique employer key.</td> 91 * </tr> 92 * <tr><td>{@link Relationship#ONE_TO_MANY}</td> 93 * <td>Array/Collection</td> 94 * <td>Unique</td> 95 * <td>A person record with multiple unique email address keys.</td> 96 * </tr> 97 * <tr><td>{@link Relationship#MANY_TO_MANY}</td> 98 * <td>Array/Collection</td> 99 * <td>Duplicates</td> 100 * <td>A person record with multiple non-unique organization 101 * keys.</td> 102 * </tr> 103 * </table> 104 * </div> 105 * 106 * <p>For a <em>many-to-x</em> relationship, the secondary index will 107 * have non-unique keys; in other words, duplicates will be allowed. 108 * Conversely, for <em>one-to-x</em> relationship, the secondary index 109 * will have unique keys.</p> 110 * 111 * <p>For a <em>x-to-one</em> relationship, the secondary key field is 112 * singular; in other words, it may not be an array or collection type. 113 * Conversely, for a <em>x-to-many</em> relationship, the secondary key 114 * field must be an array or collection type. A collection type is any 115 * implementation of {@link java.util.Collection}.</p> 116 */ 117 Relationship relate(); 118 119 /** 120 * Specifies the entity to which this entity is related, for establishing 121 * foreign key constraints. Values of this secondary key will be 122 * constrained to the set of primary key values for the given entity class. 123 * 124 * <p>The given class must be an entity class. This class is called the 125 * <em>related entity</em> or <em>foreign entity</em>.</p> 126 * 127 * <p>When a related entity class is specified, a check (foreign key 128 * constraint) is made every time a new secondary key value is stored for 129 * this entity, and every time a related entity is deleted.</p> 130 * 131 * <p>Whenever a new secondary key value is stored for this entity, it is 132 * checked to ensure it exists as a primary key value of the related 133 * entity. If it does not, a {@link DatabaseException} will be thrown 134 * by the {@link PrimaryIndex} {@code put} method.</p> 135 * 136 * <p>Whenever a related entity is deleted and its primary key value exists 137 * as a secondary key value for this entity, the action is taken that is 138 * specified using the {@link #onRelatedEntityDelete} property.</p> 139 * 140 * <p>Together, these two checks guarantee that a secondary key value for 141 * this entity will always exist as a primary key value for the related 142 * entity. Note, however, that a transactional store must be configured 143 * to guarantee this to be true in the face of a crash; see {@link 144 * StoreConfig#setTransactional}.</p> 145 */ 146 Class relatedEntity() default void.class; 147 148 /** 149 * Specifies the action to take when a related entity is deleted having a 150 * primary key value that exists as a secondary key value for this entity. 151 * 152 * <p><em>Note:</em> This property only applies when {@link #relatedEntity} 153 * is specified to define the related entity.</p> 154 * 155 * <p>The default action, {@link DeleteAction#ABORT ABORT}, means that a 156 * {@link DatabaseException} is thrown in order to abort the current 157 * transaction.</p> 158 * 159 * <p>If {@link DeleteAction#CASCADE CASCADE} is specified, then this 160 * entity will be deleted also. This in turn could trigger further 161 * deletions, causing a cascading effect.</p> 162 * 163 * <p>If {@link DeleteAction#NULLIFY NULLIFY} is specified, then the 164 * secondary key in this entity is set to null and this entity is updated. 165 * If the key field type is singular, the field value is set to null; 166 * therefore, to specify {@code NULLIFY} for a singular key field type, a 167 * primitive wrapper type must be used instead of a primitive type. If the 168 * key field type is an array or collection type, the key is deleted from 169 * the array (the array is resized) or from the collection (using {@link 170 * java.util.Collection#remove Collection.remove}).</p> 171 */ 172 DeleteAction onRelatedEntityDelete() default DeleteAction.ABORT; 173 174 /** 175 * Specifies the name of the key in order to use a name that is different 176 * than the field name. 177 * 178 * <p>This is convenient when prefixes or suffices are used on field names. 179 * For example:</p> 180 * <pre class="code"> 181 * class Person { 182 * {@literal @SecondaryKey(relate=MANY_TO_ONE, relatedEntity=Person.class, name="parentSsn")} 183 * String m_parentSsn; 184 * }</pre> 185 * 186 * <p>It can also be used to uniquely name a key when multiple secondary 187 * keys for a single entity class have the same field name. For example, 188 * an entity class and its subclass may both have a field named 'date', 189 * and both fields are used as secondary keys. The {@code name} property 190 * can be specified for one or both fields to give each key a unique 191 * name.</p> 192 */ 193 String name() default ""; 194} 195