# Fts4

Artifact: [androidx.room:room-common](https://developer.android.com/jetpack/androidx/releases/room) [View Source](https://cs.android.com/search?q=file:androidx/room/Fts4.kt+class:androidx.room.Fts4) Added in [2.1.0](https://developer.android.com/jetpack/androidx/releases/room#2.1.0)

*** ** * ** ***


```
@Target(allowedTargets = [AnnotationTarget.CLASS])
@Retention(value = AnnotationRetention.BINARY)
public annotation Fts4
```

<br />

*** ** * ** ***

Marks an `https://developer.android.com/reference/androidx/room/Entity` annotated class as a FTS4 entity. This class will have a mapping SQLite FTS4 table in the database.

FTS3 and FTS4 (https://www.sqlite.org/fts3.html) are SQLite virtual table modules that allows full-text searches to be performed on a set of documents.

An FTS entity table always has a column named `rowid` that is the equivalent of an `INTEGER PRIMARY KEY` index. Therefore, an FTS entity can only have a single field annotated with `https://developer.android.com/reference/androidx/room/PrimaryKey`, it must be named `rowid` and must be of `INTEGER` affinity. The field can be optionally omitted in the class but can still be used in queries.

All fields in an FTS entity are of `TEXT` affinity, except the for the 'rowid' and 'languageid' fields.

Example:

```
@Entity
@Fts4
data class Mail (
  @PrimaryKey
  @ColumnInfo(name = "rowid")
  val rowId: Int,
  val subject: String,
  val body: String
)
```

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/room/Entity` |   |
| `https://developer.android.com/reference/androidx/room/Dao` |   |
| `https://developer.android.com/reference/androidx/room/Database` |   |
| `https://developer.android.com/reference/androidx/room/PrimaryKey` |   |
| `https://developer.android.com/reference/androidx/room/ColumnInfo` |   |

## Summary

| ### Public methods |
|---|---|
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.reflect/-k-class/index.html<@https://developer.android.com/reference/androidx/annotation/NonNull ?>` | `https://developer.android.com/reference/androidx/room/Fts4#getContentEntity()()` The external content entity who's mapping table will be used as content for the FTS table. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/java/lang/String.html` | `https://developer.android.com/reference/androidx/room/Fts4#getLanguageId()()` The column name to be used as 'languageid'. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/room/FtsOptions.MatchInfo` | `https://developer.android.com/reference/androidx/room/Fts4#getMatchInfo()()` The FTS version used to store text matching information. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull String[]` | `https://developer.android.com/reference/androidx/room/Fts4#getNotIndexed()()` The list of column names on the FTS table that won't be indexed. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/room/FtsOptions.Order` | `https://developer.android.com/reference/androidx/room/Fts4#getOrder()()` The preferred 'rowid' order of the FTS table. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull int[]` | `https://developer.android.com/reference/androidx/room/Fts4#getPrefix()()` The list of prefix sizes to index. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/java/lang/String.html` | `https://developer.android.com/reference/androidx/room/Fts4#getTokenizer()()` The tokenizer to be used in the FTS table. |
| `final @https://developer.android.com/reference/androidx/annotation/NonNull String[]` | `https://developer.android.com/reference/androidx/room/Fts4#getTokenizerArgs()()` Optional arguments to configure the defined tokenizer. |

## Public methods

### getContentEntity

```
public final @NonNull KClass<@NonNull ?> getContentEntity()
```

The external content entity who's mapping table will be used as content for the FTS table.

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.

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.

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.

See the [External Content FTS4 Tables](https://www.sqlite.org/fts3.html#_external_content_fts4_tables_) documentation for details.

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.reflect/-k-class/index.html<@https://developer.android.com/reference/androidx/annotation/NonNull ?>` | The external content entity. |

### getLanguageId

```
public final @NonNull String getLanguageId()
```

The column name to be used as 'languageid'.

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 `INTEGER` with the same name must exist in the class.

FTS queries are affected by defining this option, see [the languageid= option documentation](https://www.sqlite.org/fts3.html#the_languageid_option) for details.

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/java/lang/String.html` | The column name to be used as 'languageid'. |

### getMatchInfo

```
public final @NonNull FtsOptions.MatchInfo getMatchInfo()
```

The FTS version used to store text matching information.

The default value is MatchInfo.FTS4. Disk space consumption can be reduced by setting this option to FTS3, see [the matchinfo= option documentation](https://www.sqlite.org/fts3.html#the_matchinfo_option) for details.

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/room/FtsOptions.MatchInfo` | The match info version, either MatchInfo.FTS4 or MatchInfo.FTS3. |

### getNotIndexed

```
public final @NonNull String[] getNotIndexed()
```

The list of column names on the FTS table that won't be indexed.

For details, see the [notindexed= option documentation](https://www.sqlite.org/fts3.html#the_notindexed_option).

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull String[]` | A list of column names that will not be indexed by the FTS extension. |

### getOrder

```
public final @NonNull FtsOptions.Order getOrder()
```

The preferred 'rowid' order of the FTS table.

The default value is Order.ASC. If many queries are run against the FTS table use `ORDER BY row DESC` then it may improve performance to set this option to Order.DESC, enabling the FTS module to store its data in a way that optimizes returning results in descending order by `rowid`.

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/androidx/room/FtsOptions.Order` | The preferred order, either Order.ASC or Order.DESC. |

### getPrefix

```
public final @NonNull int[] getPrefix()
```

The list of prefix sizes to index.

For details, [the prefix= option documentation](https://www.sqlite.org/fts3.html#the_prefix_option).

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull int[]` | A list of non-zero positive prefix sizes to index. |

### getTokenizer

```
public final @NonNull String getTokenizer()
```

The tokenizer to be used in the FTS table.

The default value is `https://developer.android.com/reference/androidx/room/FtsOptions#TOKENIZER_SIMPLE()`. Tokenizer arguments can be defined with `https://developer.android.com/reference/androidx/room/Fts4#(kotlin.String,kotlin.Array,kotlin.reflect.KClass,kotlin.String,androidx.room.FtsOptions.MatchInfo,kotlin.Array,kotlin.IntArray,androidx.room.FtsOptions.Order)`.

If a custom tokenizer is used, the tokenizer and its arguments are not verified at compile time.

For details, see [SQLite tokernizers documentation](https://www.sqlite.org/fts3.html#tokenizer)

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull https://developer.android.com/reference/java/lang/String.html` | The tokenizer to use on the FTS table. Built-in available tokenizers are `https://developer.android.com/reference/androidx/room/FtsOptions#TOKENIZER_SIMPLE()`, `https://developer.android.com/reference/androidx/room/FtsOptions#TOKENIZER_PORTER()` and `https://developer.android.com/reference/androidx/room/FtsOptions#TOKENIZER_UNICODE61()`. |

| See also |
|---|---|
| `https://developer.android.com/reference/androidx/room/Fts4#(kotlin.String,kotlin.Array,kotlin.reflect.KClass,kotlin.String,androidx.room.FtsOptions.MatchInfo,kotlin.Array,kotlin.IntArray,androidx.room.FtsOptions.Order)` |   |

### getTokenizerArgs

```
public final @NonNull String[] getTokenizerArgs()
```

Optional arguments to configure the defined tokenizer.

Tokenizer arguments consist of an argument name, followed by an "=" character, followed by the option value. For example, `separators=.` defines the dot character as an additional separator when using the `https://developer.android.com/reference/androidx/room/FtsOptions#TOKENIZER_UNICODE61()` tokenizer.

The available arguments that can be defined depend on the tokenizer defined, see the [SQLite tokenizers documentation](https://www.sqlite.org/fts3.html#tokenizer) for details.

| Returns |
|---|---|
| `@https://developer.android.com/reference/androidx/annotation/NonNull String[]` | A list of tokenizer arguments strings. |