GORM mapping: make an index unique

I'm feeling a little slow today. I'm trying to do something that I think is very simple. I have a Domain class with a property called 'name'. I want 'name' to have an index, and I want the index to require that the 'name' is unique. I've set the unique constraint and tried creating an index. I can't make sense out of the Gorm docs as to how I add the unique attribute to the index. Here's some code:

class Project {
    String name

    static hasMany = [things:Things]

    static mapping = {
        name index:'name_idx'
    }
    static constraints = {
        name(unique:true)
    }
}

All is well with the above, except when do "show indexes from project" in mysql it shows my name key as not unique. I know the problem is that I am not specifying unique in the mapping, but quite frankly the docs for gorm are making my head hurt. I see all kinds of stuff about columns, but I can't find a single example anywhere on the web that shows what I want to do. I don't need complex mappings or compound keys, I just want to know the syntax to add the unique attribute to the mapping declaration above. Any advice welcome.

I also did a开发者_StackOverflow grails export-schema and see the following:

create index name_idx on project (name);

Nothing in that to indicate this index requires unique values

A related followup question would be once I succeed in making that index unique, what type of error should I expect when I go to save a Project instance and the name is not unique? Is there a specific exception thrown? I realize that even if I check that a given 'name' is unique there's still a possibility that by the time I save it there may be a row with that name.

I'm quite sure the syntax to do what I want is simple but I just can't find a simple example to educate myself with. I've been to this page but it doesn't explain HOW the uniqueness is enforced. I'd like to enforce it at the name index level.

The indexColumn allows additional options to be configured. This may be what you're looking for.

static mapping = {
    name indexColumn:[name:'name_idx', unique:true]
}

Grails Documentation for indexColumn

If you put only the unique constraint the GORM send DDL to create an unique index on database.

static constraints = {
   name nullable: false, unique: true
}