| /* |
| * Copyright (C) 2017 The Android Open Source Project |
| * |
| * 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 android.arch.persistence.room; |
| |
| import java.lang.annotation.Retention; |
| import java.lang.annotation.RetentionPolicy; |
| import java.lang.annotation.Target; |
| |
| /** |
| * Declares an index on an Entity. |
| * see: <a href="https://sqlite.org/lang_createindex.html">SQLite Index Documentation</a> |
| * <p> |
| * Adding an index usually speeds up your select queries but will slow down other queries like |
| * insert or update. You should be careful when adding indices to ensure that this additional cost |
| * is worth the gain. |
| * <p> |
| * There are 2 ways to define an index in an {@link Entity}. You can either set |
| * {@link ColumnInfo#index()} property to index individual fields or define composite indices via |
| * {@link Entity#indices()}. |
| * <p> |
| * If an indexed field is embedded into another Entity via {@link Embedded}, it is <b>NOT</b> |
| * added as an index to the containing {@link Entity}. If you want to keep it indexed, you must |
| * re-declare it in the containing {@link Entity}. |
| * <p> |
| * Similarly, if an {@link Entity} extends another class, indices from the super classes are |
| * <b>NOT</b> inherited. You must re-declare them in the child {@link Entity} or set |
| * {@link Entity#inheritSuperIndices()} to {@code true}. |
| * */ |
| @Target({}) |
| @Retention(RetentionPolicy.CLASS) |
| public @interface Index { |
| /** |
| * List of column names in the Index. |
| * <p> |
| * The order of columns is important as it defines when SQLite can use a particular index. |
| * See <a href="https://www.sqlite.org/optoverview.html">SQLite documentation</a> for details on |
| * index usage in the query optimizer. |
| * |
| * @return The list of column names in the Index. |
| */ |
| String[] value(); |
| |
| /** |
| * Name of the index. If not set, Room will set it to the list of columns joined by '_' and |
| * prefixed by "index_${tableName}". So if you have a table with name "Foo" and with an index |
| * of {"bar", "baz"}, generated index name will be "index_Foo_bar_baz". If you need to specify |
| * the index in a query, you should never rely on this name, instead, specify a name for your |
| * index. |
| * |
| * @return The name of the index. |
| */ |
| String name() default ""; |
| |
| /** |
| * If set to true, this will be a unique index and any duplicates will be rejected. |
| * |
| * @return True if index is unique. False by default. |
| */ |
| boolean unique() default false; |
| } |