MapColumn

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    @Target(allowedTargets = [AnnotationTarget.TYPE])
    @Retention(value = AnnotationRetention.BINARY)
    annotation MapColumn

Declares which column is used to build a map or multimap return value in a Dao query method.

This annotation is required when the key or value of a Map (or nested map) is a single column of one of the built in types (primitives, boxed primitives, enum, String, byte[], ByteBuffer) or a type with a converter (e.g. Date, UUID, etc).

The use of this annotation provides clarity on which column should be used in retrieving information required by the return type.

Example:

@Query("SELECT * FROM Artist JOIN Song ON Artist.artistName = Song.artist")
fun getArtistNameToSongNames():
Map<@MapColumn(columnName = "artistName") String,
@MapColumn(columnName = "songName") List<String>>

@Query("SELECT *, COUNT(mSongId) as songCount FROM Artist JOIN Song ON
Artist.artistName = Song.artist GROUP BY artistName")
fun getArtistAndSongCounts(): Map<Artist, @MapColumn(columnName = "songCount") Integer>

Column(s) specified in the provided @MapColumn annotation must be present in the query result.

Summary

Public constructors
MapColumn(columnName: String, tableName: String)
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Public properties
String

The name of the column to be used for the map's key or value.
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String

The name of the table or alias to be used for the map's column.
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Public constructors

MapColumn

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MapColumn(columnName: String, tableName: String = "")

Public properties

columnName

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val columnName: String

The name of the column to be used for the map's key or value.

Returns
String

The column name.

tableName

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val tableName: String

The name of the table or alias to be used for the map's column.

Providing this value is optional. Useful for disambiguating between duplicate column names. For example, consider the following query: SELECT * FROM Artist AS a JOIN Song AS s ON a.id == s.artistId, then the @MapColumn for a return type Map<String, List<Song>> would be Map<@MapColumn(columnName = "id", tableName = "a") String, List<Song>>.

Returns
String

The column table name.