EDIT: Note that this approach does not consider a unique(article_id , tags_id) constraint. It also raises an issue with two Articles having the same tags. - Sorry.
While this is not officially documented (see the relevant parts of the Grails Reference Documentation here and here) constraints on one-to-many associations are simply ignored by GORM. This includes unique and nullable constraints, and probably any.
This can be proved by setting dbCreate="create" and next, by looking at the database schema definition. For your Article sample and the PostgreSQL database, this would be:
CREATE TABLE article_tags
(
article_id bigint NOT NULL,
tags_string character varying(255),
CONSTRAINT fkd626473e45ef9ffb FOREIGN KEY (article_id)
REFERENCES article (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT article0_tags_article0_id_key UNIQUE (article_id)
)
WITH (
OIDS=FALSE
);
As can be seen above, there are no constraints for the tags_string column.
In contrast to constraints on association fields, constraints on "normal" instance fields of domain classes do work as expected.
Thus, we'll want to have some kind of Tag, or TagHolder, domain class, and we'd need to find a pattern that still provides the Article with a clean public API.
First, we're introducing the TagHolder domain class:
class TagHolder {
String tag
static constraints = {
tag(unique:true, nullable:false,
blank:false, size:2..255)
}
}
and associate it with the Article class:
class Article {
String text
static hasMany = [tagHolders: TagHolder]
}
In order to provide a clean public API, we're adding the methods String[] getTags(), void setTags(String[]. That way, we can also call the constructor with named parameters, like, new Article(text: "text", tags: ["foo", "bar"]). We're also adding the addToTags(String) closure, which mimicks GORM's corresponding "magic method".
class Article {
String text
static hasMany = [tagHolders: TagHolder]
String[] getTags() {
tagHolders*.tag
}
void setTags(String[] tags) {
tagHolders = tags.collect { new TagHolder(tag: it) }
}
{
this.metaClass.addToTags = { String tag ->
tagHolders = tagHolders ?: []
tagHolders << new TagHolder(tag: tag)
}
}
}
It's a workaround, but there's not too much coding involved.
A drawback, we're getting an additional JOIN table. Nevertheless, this pattern allows for applying any available constraints.
Finally, a test case could look like this one:
class ArticleTests extends GroovyTestCase {
void testUniqueTags_ShouldFail() {
shouldFail {
def tags = ["foo", "foo"] // tags not unique
def article = new Article(text: "text", tags: tags)
assert ! article.validate()
article.save()
}
}
void testUniqueTags() {
def tags = ["foo", "bar"]
def article = new Article(text: "text", tags: tags)
assert article.validate()
article.save()
assert article.tags.size() == 2
assert TagHolder.list().size() == 2
}
void testTagSize_ShouldFail() {
shouldFail {
def tags = ["f", "b"] // tags too small
def article = new Article(text: "text", tags: tags)
assert ! article.validate()
article.save()
}
}
void testTagSize() {
def tags = ["foo", "bar"]
def article = new Article(text: "text", tags: tags)
assert article.validate()
article.save()
assert article.tags.size() == 2
assert TagHolder.list().size() == 2
}
void testAddTo() {
def article = new Article(text: "text")
article.addToTags("foo")
article.addToTags("bar")
assert article.validate()
article.save()
assert article.tags.size() == 2
assert TagHolder.list().size() == 2
}
}