info.archinnov.achilles.annotations

Annotation Type Computed

@Retention(value=RUNTIME)
 @Target(value=FIELD)
 @Documented
public @interface Computed

Annotation for computed column. A computed column is a column obtained by applying a CQL function on other(s) column(s). A computed column can only be referenced in SELECT/read statements, not UPDATE/INSERT/DELETE
Examples:

 //Normal column name
 @Column(name = "first_name")
 private String firstName;

 //Write time of firstName
 @Column
 @Computed(function = "writetime", alias = "write_time", targetColumns = "first_name", cqlClass = Long.class)
 private Long firstNameWriteTime;
 

In the above example, the field firstNameWriteTime is obtained by applying the function writime on the column first_name. The target CQL class is Long.
Please note that the targerFields should reference CQL column names, not Java field name. In the example it should be "first_name" and not "firstName"

This annotation will generate the following SELECT statement at runtime:

 SELECT first_name, writetime(first_name) AS write_time ....
 

See Also:

@Computed

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String	alias Mandatory.
Class<?>	cqlClass Mandatory.
String	function Mandatory.
String[]	targetColumns Mandatory.

Element Detail

function

public abstract String function

Mandatory. The name of the CQL function to be used.

alias

public abstract String alias

Mandatory. The alias of this computed column. Warning: if you have multiple computed columns in the same entity, please take care to choose different alias

targetColumns

public abstract String[] targetColumns

Mandatory. The target CQL columns on which the function will be applied. You can passe in multiple columns. The ordering of columns does matter

cqlClass

public abstract Class<?> cqlClass

Mandatory. To help Achilles determine the CQL type at compile time, you have to specify the Cassandra Java data type produced by the function application. This type should be a CQL-compatible type.
Example: the writetime function will produce a CQL bigint so it's corresponding Java type is Long