androidx.room.Index Maven / Gradle / Ivy
Show all versions of android-all Show documentation
/*
* 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 androidx.room;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Declares an index on an Entity.
* see: SQLite Index Documentation
*
* 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.
*
* 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()}.
*
* If an indexed field is embedded into another Entity via {@link Embedded}, it is NOT
* 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}.
*
* Similarly, if an {@link Entity} extends another class, indices from the super classes are
* NOT 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.
*
* The order of columns is important as it defines when SQLite can use a particular index.
* See SQLite documentation 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;
}