(Quick Reference)

7.5.2.1 Table and Column Names - Reference Documentation

Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith, Lari Hotari

Version: 3.1.9

7.5.2.1 Table and Column Names

Table names

The database table name which the class maps to can be customized using the table method:

class Person {
    …
    static mapping = {
        table 'people'
    }
}

In this case the class would be mapped to a table called people instead of the default name of person.

Column names

It is also possible to customize the mapping for individual columns onto the database. For example to change the name you can do:

class Person {

String firstName

static mapping = { table 'people' firstName column: 'First_Name' } }

Here firstName is a dynamic method within the mapping Closure that has a single Map parameter. Since its name corresponds to a domain class persistent field, the parameter values (in this case just "column") are used to configure the mapping for that property.

Column type

GORM supports configuration of Hibernate types with the DSL using the type attribute. This includes specifying user types that implement the Hibernate org.hibernate.usertype.UserType interface, which allows complete customization of how a type is persisted. As an example if you had a PostCodeType you could use it as follows:

class Address {

String number String postCode

static mapping = { postCode type: PostCodeType } }

Alternatively if you just wanted to map it to one of Hibernate's basic types other than the default chosen by Grails you could use:

class Address {

String number String postCode

static mapping = { postCode type: 'text' } }

This would make the postCode column map to the default large-text type for the database you're using (for example TEXT or CLOB).

See the Hibernate documentation regarding Basic Types for further information.

Many-to-One/One-to-One Mappings

In the case of associations it is also possible to configure the foreign keys used to map associations. In the case of a many-to-one or one-to-one association this is exactly the same as any regular column. For example consider the following:

class Person {

String firstName Address address

static mapping = { table 'people' firstName column: 'First_Name' address column: 'Person_Address_Id' } }

By default the address association would map to a foreign key column called address_id. By using the above mapping we have changed the name of the foreign key column to Person_Adress_Id.

One-to-Many Mapping

With a bidirectional one-to-many you can change the foreign key column used by changing the column name on the many side of the association as per the example in the previous section on one-to-one associations. However, with unidirectional associations the foreign key needs to be specified on the association itself. For example given a unidirectional one-to-many relationship between Person and Address the following code will change the foreign key in the address table:

class Person {

String firstName

static hasMany = [addresses: Address]

static mapping = { table 'people' firstName column: 'First_Name' addresses column: 'Person_Address_Id' } }

If you don't want the column to be in the address table, but instead some intermediate join table you can use the joinTable parameter:

class Person {

String firstName

static hasMany = [addresses: Address]

static mapping = { table 'people' firstName column: 'First_Name' addresses joinTable: [name: 'Person_Addresses', key: 'Person_Id', column: 'Address_Id'] } }

Many-to-Many Mapping

Grails, by default maps a many-to-many association using a join table. For example consider this many-to-many association:

class Group {
    …
    static hasMany = [people: Person]
}

class Person {
    …
    static belongsTo = Group
    static hasMany = [groups: Group]
}

In this case Grails will create a join table called group_person containing foreign keys called person_id and group_id referencing the person and group tables. To change the column names you can specify a column within the mappings for each class.

class Group {
   …
   static mapping = {
       people column: 'Group_Person_Id'
   }
}
class Person {
   …
   static mapping = {
       groups column: 'Group_Group_Id'
   }
}

You can also specify the name of the join table to use:

class Group {
   …
   static mapping = {
       people column: 'Group_Person_Id',
              joinTable: 'PERSON_GROUP_ASSOCIATIONS'
   }
}
class Person {
   …
   static mapping = {
       groups column: 'Group_Group_Id',
              joinTable: 'PERSON_GROUP_ASSOCIATIONS'
   }
}