1 /* 2 * Copyright (C) 2017 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package androidx.room; 18 19 import java.lang.annotation.Retention; 20 import java.lang.annotation.RetentionPolicy; 21 import java.lang.annotation.Target; 22 23 /** 24 * Declares an index on an Entity. 25 * see: <a href="https://sqlite.org/lang_createindex.html">SQLite Index Documentation</a> 26 * <p> 27 * Adding an index usually speeds up your select queries but will slow down other queries like 28 * insert or update. You should be careful when adding indices to ensure that this additional cost 29 * is worth the gain. 30 * <p> 31 * There are 2 ways to define an index in an {@link Entity}. You can either set 32 * {@link ColumnInfo#index()} property to index individual fields or define composite indices via 33 * {@link Entity#indices()}. 34 * <p> 35 * If an indexed field is embedded into another Entity via {@link Embedded}, it is <b>NOT</b> 36 * added as an index to the containing {@link Entity}. If you want to keep it indexed, you must 37 * re-declare it in the containing {@link Entity}. 38 * <p> 39 * Similarly, if an {@link Entity} extends another class, indices from the super classes are 40 * <b>NOT</b> inherited. You must re-declare them in the child {@link Entity} or set 41 * {@link Entity#inheritSuperIndices()} to {@code true}. 42 * */ 43 @Target({}) 44 @Retention(RetentionPolicy.CLASS) 45 public @interface Index { 46 /** 47 * List of column names in the Index. 48 * <p> 49 * The order of columns is important as it defines when SQLite can use a particular index. 50 * See <a href="https://www.sqlite.org/optoverview.html">SQLite documentation</a> for details on 51 * index usage in the query optimizer. 52 * 53 * @return The list of column names in the Index. 54 */ 55 String[] value(); 56 57 /** 58 * Name of the index. If not set, Room will set it to the list of columns joined by '_' and 59 * prefixed by "index_${tableName}". So if you have a table with name "Foo" and with an index 60 * of {"bar", "baz"}, generated index name will be "index_Foo_bar_baz". If you need to specify 61 * the index in a query, you should never rely on this name, instead, specify a name for your 62 * index. 63 * 64 * @return The name of the index. 65 */ 66 String name() default ""; 67 68 /** 69 * If set to true, this will be a unique index and any duplicates will be rejected. 70 * 71 * @return True if index is unique. False by default. 72 */ 73 boolean unique() default false; 74 } 75
