(Quick Reference)
discriminator
Purpose
Customizes the discriminator value used in table-per-subclass inheritance mapping.
Examples
class Content {
…
}
class PodCast extends Content {
…
static mapping = {
discriminator "audio"
}
}Description
Usage:
discriminator(string/map)Arguments:
column (optional) - The column name to store the discriminatorvalue - The value to use for the discriminatorformula (optional) - an SQL expression that is executed to evaluate the type of class. Use this or column but not bothtype (optional defaults to string) - the Hibernate type, used for the where clause condition to know if it needs to wrap it with ' or not
By default when mapping inheritance Grails uses a single-table model so that all subclasses share the same table. A discriminator column is then used to help Grails tell what type a particular row is. By default the class name is stored as the value of this column. You can use the
discriminator method to customize the value stored:
class Content {
…
}
class PodCast extends Content {
…
static mapping = {
discriminator "audio"
}
}You can also customize the discriminator column name:
class Content {
…
static mapping = {
discriminator column:"content_type"
}
}
class PodCast extends Content {
…
static mapping = {
discriminator value: "audio"
}
}Or you can use a formula:
class Content {
…
static mapping = {
discriminator value: "1", type: "integer",
formula: "case when CLASS_TYPE in ('a', 'b', 'c') then 0 else 1 end"
}
}
class PodCast extends Content{
…
static mapping = {
discriminator value: "0"
}
}
