Index

Kotlin |Java

@Target([]) class Index

androidx.room.Index

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 Entity. You can either set ColumnInfo#index() property to index individual fields or define composite indices via Entity#indices().

If an indexed field is embedded into another Entity via Embedded, it is NOT added as an index to the containing Entity. If you want to keep it indexed, you must re-declare it in the containing Entity.

Similarly, if an Entity extends another class, indices from the super classes are NOT inherited. You must re-declare them in the child Entity or set Entity#inheritSuperIndices() to true.

Summary

Public constructors
<init>(vararg value: String, name: String, unique: Boolean) Declares an index on an Entity.

Properties
String	name Name of the index.
Boolean	unique If set to true, this will be a unique index and any duplicates will be rejected.
Array<String>	value List of column names in the Index.

Public constructors

<init>

Index(
    vararg value: String, 
    name: String, 
    unique: Boolean)

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 Entity. You can either set ColumnInfo#index() property to index individual fields or define composite indices via Entity#indices().

If an indexed field is embedded into another Entity via Embedded, it is NOT added as an index to the containing Entity. If you want to keep it indexed, you must re-declare it in the containing Entity.

Similarly, if an Entity extends another class, indices from the super classes are NOT inherited. You must re-declare them in the child Entity or set Entity#inheritSuperIndices() to true.

Properties

name

val name: String

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
String: The name of the index.

unique

val unique: Boolean

If set to true, this will be a unique index and any duplicates will be rejected.

Return
Boolean: True if index is unique. False by default.

value

val value: Array<String>

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
Array<String>: The list of column names in the Index.