Groovy way of doing it in Grails - grails

Question

Article {
String categoryName
static hasMany = [
tags: Tag
]
}
Tag {
String name
}
Now I want to find the list of all related articles. Related meaning, all articles that have the same category name as myArticle or any of the same tags as myArtcle.
With only matching categoryName, here is how I would get the relatedArticles using closures.
def relatedArticles = Article.list().find {it.categoryName == myArticle.categoryName }
Anyone wants to give a shot to find all articles by CategoryName or Tag Name (in a groovy way)?
Any solutions using Criteria or custom queries is appreciated too.

Answer 1

This would work:
def myArticle = // the article you want to match
def relatedArticles = Article.list().findAll {
(it.categoryName == myArticle.categoryName ||
it.tags.name.intersect(myArticle.tags.name)) &&
it.id != myArticle.id)
}
However, if you have a reasonably large number of articles and only a small number of them are expected to match it would be horribly inefficient, as this will load all articles then iterate through them all looking for matches.
A better way would be to simply write a query that only loads matching articles (instead of calling Article.list())

Answer 2

I think that you need to use a separate query per article tag:
// Use a LinkedHashSet to retain the result order if that is important
def results = new LinkedHashSet()
results.addAll(Article.findAll("from Article as article \
where article.categoryName = :categoryName \
and article.id != :id",
[
categoryName:myArticle.categoryName,
id:myArticle.id,
])
myArticle.tags.each {
results.addAll(Article.executeQuery(
"select distinct article from Article as article, \
Tag as tag \
where tag.name = :tag \
and tag in elements(article.tags) \
and article.id != :id",
[
tag:it.name,
id:myArticle.id,
]))
}
def relatedArticles = results as List
This is obviously worthwhile doing when you have a lot of content in the system and wish to avoid loading the entire database for a single page request. Other improvements include specifying max and offset parameters to the queries.

Answer 3

Ideally, you'd use Criteria Query, bug since you said you are not concerned about performance, something like this should work:
def category =
def tagName
def relatedArticles = Article.list().findAll {
(it.categoryName == myArticle.categoryName) || ( it.tags.contains(tagName) )
}