Add persistence support to Collections and Maps of basic (no domain classes) types

First of all, it must be decided on how to store the collection of basic types in a relational database.

Option 1:
Use JDBC ARRAY type.

Option 2:
Use Java serialization to store the whole collection in a column of byte array. (BLOB or VARBINARY or LONGVARBINARY).

Option 3:
Use XML serialization to store the whole collection in a column of VARCHAR or LONGVARCHAR.

Option 4:
Store the collection in a separate table.

Option 5:
Hacks, such as comma-delimited String... What about having a comma in a String element? What about various types within one array?

As there are workarounds, I propose to lower the priority to 'Minor'.

Hi, option 5 breaks database 1st normal form.

I think separating the tables is a good option. Maybe it's a good idea to set the table name to something that denotes that is a table of datavalues and not a mapping from a domain class, something like: string_collection_1234 or string_map_3214, and the mapping table of the domain class that has this attribute (collection or map of strings) reference to those table names, I'm only thinking about it, I dont know very much about how hibernate works.

Looks like Hibernate supports collections of basic types by creating a dedicated table. The mapping looks like this:

<set name="names" table="person_names">
    <key column="person_id"/>
    <element column="person_name" type="string"/>
</set>

More info here:

http://www.hibernate.org/hib_docs/v3/reference/en/html/collections.html#collections-ofvalues

Hi, I am also trying to do this, like this:

class NetworkOperator{
String name
HashMap otherNames = new HashMap()

static hasMany = [otherNames:String]
}

I would expect this to work in a dedicated table, I will probably use Peter's Hibernate manual mapping for now. It would be very nice if grails could do this on it's own... Thanks!

GORM now supports basic collection types using a join table:

class Person {
    static hasMany = [nicknames:String]
}

Grails will map a new join table called "person_nicknames":

You can change the mapping using the joinTable argument:

class Person {
    static hasMany = [nicknames:String]

    static mapping = {
       hasMany joinTable:[name:'bunch_o_nicknames', key:'person_id', column:'nickname', type:"text"]       
    } 
}

minor edit made to description of fix