GORM - change 3 queries into 1 (or at least 2) - grails

Question

I have such entities, stored in database using GORM (I omitted irrelevant fields):
class Payment {
static hasMany = [paymentEntries: PaymentEntry]
}
class PaymentEntry {
static hasOne = [category: PaymentCategory]
static belongsTo = [payment: Payment]
static constraints = {
category(nullable: true)
}
}
class PaymentCategory {
static hasMany = [payments: PaymentEntry, rules: PaymentRule]
String name
}
So we have Payments on the top, which can have many PaymentEntryies, and each PaymentEntry can belong to one PaymentCategory.
I need to select Payments, which meet some conditions, but only the ones that also have PaymentEntries belonging to specific categories. Currently I do it in 3 queries:
Select categories which fit to part of category name, or just omit category query (in such case we want all the payments regardless of their entries category):
private static List<PaymentCategory> getCategories(String category) {
def result = null
if (category != null && category.length() > 0) {
def c = PaymentCategory.createCriteria()
result = c {
ilike("name", "%${category}%")
}
}
result
}
Select PaymentEntries ids, based on PaymentCategory:
private static List<Long> paymentEntryIds(String category) {
def categories = getCategories(category)
def c = PaymentEntry.createCriteria()
def result = new ArrayList()
// If category is selected, but there is no matching category, return empty list
if (!categorySelectedButNoMatch(category, categories)) {
result = c {
if (category == null) {
isNull("category")
} else if (categories != null && categories.size() > 0) {
inList("category", categories)
}
projections {
property("id")
}
}
}
result
}
Finally select Payments, limited to the ones that contain specific PaymentEntries:
def paymentEntriesIds = paymentEntryIds(selectedCategory)
def c = Payment.createCriteria()
def result = new ArrayList()
// If there are no payment entries matching category criteria, we return empty list anyway, so there
// is no need querying payments.
if (paymentEntriesIds.size() > 0) {
result = c {
paymentEntries {
inList("id", paymentEntriesIds)
}
if (importEntryId != null) {
eq("importEntry.id", importEntryId)
}
if (query != null) {
ilike("description", query)
}
// Omitted ordering and paging
}
}
result
This works, but it runs 3 queries to the database. I'm pretty sure this code could be cleaner, and it could be done in less queries. All the ideas on how to improve it are welcome.

Answer 1

You can use at least 3 different methods: detached queries, subqueries of where queries and subqueries of HQL.
Example of DetachedQuery with criteria looks like:
def subquery = new DetachedCriteria(PaymentCategory).build {
projections {
groupProperty 'id'
}
ilike("name", "%${category}%")
}
Then you can use this subquery in another query:
return PaymentEntry.createCriteria().list {
category {
inList "id", subquery
}
}
I didn't test it on your domain exactly, this should just show the idea. Refer to DetachedCriteria part of GORM documentation: https://grails.github.io/grails-doc/latest/guide/single.html#detachedCriteria
We use it for some very complicated queries. Sometimes createAlias will be required to correctly work with associations.