(Quick Reference)

discriminator

目的
Purpose

Customizes the discriminator column used in table-per-subclass inheritance mapping.

使用例
Examples

class Content {
    …
}

class PodCast extends Content {
    …
    static mapping = {
        discriminator "audio"
    }
}

詳細
Description

Usage: discriminator(string/map)
使用方法:
Usage:
discriminator(string/map)

引数:

Arguments:
  • column (optional) - The column name to store the discriminator
  • value - The value to use for the discriminator
  • formula (optional) - an SQL expression that is executed to evaluate the type of class. Use this or column but not both
  • type (optional defaults to string) - the Hibernate type, used for the where clause condition to know if it needs to wrap it with '

By default when mapping inheritance Grails uses a single-table model where all classes share the same table. A discriminator column is used to determine the type for each row, by default the full class name. You can use the discriminator method to customize what's 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"
    }
}