GORM criteria group by in subquery - mysql

Question

Let's assume the following Grails domains:
Owner {
String name
static hasMany [cars: Cars]
}
Car {
Date inspectionDate
}
I want to be able to search for Owners through Criteria, with the following rule: Most recent Car by inspectionDate in Owner's cars list being lower than *given date*.
As an example, I want to apply the following code to a select query in GORM:
queryResultsList = allOwnersList.filter { owner ->
owner.cars.min{ car -> car.inspectionDate }.inspectionDate < myDate
}
I need to achieve it using Criteria because I am already filtering Owners on other fields.
The whole given code is used as an example, some parts of the original code has been ommited, and source code is not about cars and owners.
As on first thought I assumed I needed a subquery in SQL to retrieve my data as I expected, I tried the following:
Owner.createCriteria().list {
// [...] some filters on other fields
cars {
lt('inspectionDate', params.inspectionDate)
'in'('inspectionDate', new grails.gorm.DetachedCriteria(Owner).list {
projections {
cars {
min('inspectionDate')
}
}
})
}
}
I also tried to add groupProperty in different places in the projection, ending with MissingPropertyException.
I am using Grails 2.2.4

Answer 1

After a few days testing solutions, I've come to the following one:
Owner.createCriteria().list {
// [...] some filters on other fields
cars {
lt('inspectionDate', params.inspectionDate)
'in'('inspectionDate', Owner.createCriteria().list {
projections {
cars {
min('inspectionDate')
}
groupProperty 'id'
}
// this allows to only get first property, which is inspectionDate
}.collect { it[0] })
}
}
However, I still feel like doing things wrong. In particular, the collect part looks like a code smell.
I am posting this because it does what I need, but any help with finding a good solution will be appreciated.