Fts4.java
/*
* Copyright 2018 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 static androidx.room.FtsOptions.TOKENIZER_SIMPLE;
import androidx.annotation.RequiresApi;
import androidx.room.FtsOptions.MatchInfo;
import androidx.room.FtsOptions.Order;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Marks an {@link Entity} annotated class as a FTS4 entity. This class will have a mapping SQLite
* FTS4 table in the database.
* <p>
* <a href="https://www.sqlite.org/fts3.html">FTS3 and FTS4</a> are SQLite virtual table modules
* that allows full-text searches to be performed on a set of documents.
* <p>
* An FTS entity table always has a column named <code>rowid</code> that is the equivalent of an
* <code>INTEGER PRIMARY KEY</code> index. Therefore, an FTS entity can only have a single field
* annotated with {@link PrimaryKey}, it must be named <code>rowid</code> and must be of
* <code>INTEGER</code> affinity. The field can be optionally omitted in the class but can still be
* used in queries.
* <p>
* All fields in an FTS entity are of <code>TEXT</code> affinity, except the for the 'rowid' and
* 'languageid' fields.
* <p>
* Example:
* <pre>
* {@literal @}Entity
* {@literal @}Fts4
* public class Mail {
* {@literal @}PrimaryKey
* {@literal @}ColumnInfo(name = "rowid")
* private final int rowId;
* private final String subject;
* private final String body;
*
* public Mail(int rowId, String subject, String body) {
* this.rowId = rowId;
* this.subject = subject;
* this.body = body;
* }
*
* public String getRowId() {
* return rowId;
* }
* public String getSubject() {
* return subject;
* }
* public void getBody() {
* return body;
* }
* }
* </pre>
*
* @see Entity
* @see Dao
* @see Database
* @see PrimaryKey
* @see ColumnInfo
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.CLASS)
@RequiresApi(16)
public @interface Fts4 {
/**
* The tokenizer to be used in the FTS table.
* <p>
* The default value is {@link FtsOptions#TOKENIZER_SIMPLE}. Tokenizer arguments can be defined
* with {@link #tokenizerArgs()}.
* <p>
* If a custom tokenizer is used, the tokenizer and its arguments are not verified at compile
* time.
*
* @return The tokenizer to use on the FTS table. Built-in available tokenizers are
* {@link FtsOptions#TOKENIZER_SIMPLE}, {@link FtsOptions#TOKENIZER_PORTER} and
* {@link FtsOptions#TOKENIZER_UNICODE61}.
* @see #tokenizerArgs()
* @see <a href="https://www.sqlite.org/fts3.html#tokenizer">SQLite tokernizers
* documentation</a>
*/
String tokenizer() default TOKENIZER_SIMPLE;
/**
* Optional arguments to configure the defined tokenizer.
* <p>
* Tokenizer arguments consist of an argument name, followed by an "=" character, followed by
* the option value. For example, <code>separators=.</code> defines the dot character as an
* additional separator when using the {@link FtsOptions#TOKENIZER_UNICODE61} tokenizer.
* <p>
* The available arguments that can be defined depend on the tokenizer defined, see the
* <a href="https://www.sqlite.org/fts3.html#tokenizer">SQLite tokernizers documentation</a> for
* details.
*
* @return A list of tokenizer arguments strings.
*/
String[] tokenizerArgs() default {};
/**
* The external content entity who's mapping table will be used as content for the FTS table.
* <p>
* Declaring this value makes the mapping FTS table of this entity operate in "external content"
* mode. In such mode the FTS table does not store its own content but instead uses the data in
* the entity mapped table defined in this value. This option allows FTS4 to forego storing the
* text being indexed which can be used to achieve significant space savings.
* <p>
* In "external mode" the content table and the FTS table need to be synced. Room will create
* the necessary triggers to keep the tables in sync. Therefore, all write operations should
* be performed against the content entity table and not the FTS table.
* <p>
* The content sync triggers created by Room will be removed before migrations are executed and
* are re-created once migrations are complete. This prevents the triggers from interfering with
* migrations but means that if data needs to be migrated then write operations might need to be
* done in both the FTS and content tables.
*
* @return The external content entity.
* @see <a href="https://www.sqlite.org/fts3.html#_external_content_fts4_tables_">External
* Content FTS4 Tables</a>
*/
Class<?> contentEntity() default Object.class;
/**
* The column name to be used as 'languageid'.
* <p>
* Allows the FTS4 extension to use the defined column name to specify the language stored in
* each row. When this is defined a field of type <code>INTEGER</code> with the same name must
* exist in the class.
* <p>
* FTS queries are affected by defining this option, see
* <a href=https://www.sqlite.org/fts3.html#the_languageid_option>the languageid= option
* documentation</a> for details.
*
* @return The column name to be used as 'languageid'.
*/
String languageId() default "";
/**
* The FTS version used to store text matching information.
* <p>
* The default value is {@link MatchInfo#FTS4}. Disk space consumption can be reduced by
* setting this option to FTS3, see
* <a href=https://www.sqlite.org/fts3.html#the_matchinfo_option>the matchinfo= option
* documentation</a> for details.
*
* @return The match info version, either {@link MatchInfo#FTS4} or {@link MatchInfo#FTS3}.
*/
MatchInfo matchInfo() default MatchInfo.FTS4;
/**
* The list of column names on the FTS table that won't be indexed.
*
* @return A list of column names that will not be indexed by the FTS extension.
* @see <a href="https://www.sqlite.org/fts3.html#the_notindexed_option">The notindexed= option
* documentation</a>
*/
String[] notIndexed() default {};
/**
* The list of prefix sizes to index.
*
* @return A list of non-zero positive prefix sizes to index.
* @see <a href="https://www.sqlite.org/fts3.html#the_prefix_option">The prefix= option
* documentation</a>
*/
int[] prefix() default {};
/**
* The preferred 'rowid' order of the FTS table.
* <p>
* The default value is {@link Order#ASC}. If many queries are run against the FTS table use
* <code>ORDER BY row DESC</code> then it may improve performance to set this option to
* {@link Order#DESC}, enabling the FTS module to store its data in a way that optimizes
* returning results in descending order by rowid.
*
* @return The preferred order, either {@link Order#ASC} or {@link Order#DESC}.
*/
Order order() default Order.ASC;
}