How do we compose queries in Kotlin Exposed? - kotlin

Question

I would like to create something similar to Ruby's ActiveRecord Scopes using Kotlin Exposed.
For example I would like to break the following query up so that the first part acts like a scope.
This query returns what I want.
val m1 = Measurement.wrapRows(Measurements.innerJoin(Runs).select {
((exists(Tags.select { Tags.run.eq(Runs.sequelId) and Tags.name.eq("region") and Tags.value.eq("default") })) or notExists(Tags.select {
Tags.run.eq(Runs.sequelId) and Tags.name.eq("region")
})) and Measurements.name.eq("someName")
I would like to use this part as a scope:
val q1 = Measurements.innerJoin(Runs).select {
((exists(Tags.select { Tags.run.eq(Runs.sequelId) and Tags.name.eq("region") and Tags.value.eq("default") })) or notExists(Tags.select {
Tags.run.eq(Runs.sequelId) and Tags.name.eq("region")
}))
}
and then be able to refine the query using the q1 "scope"
so something like this:
val q2 = q1.having { Measurements.name.eq("someName") } // which does not work
Ultimately I would like to push this down into either the Measurements object or the Measurement class so I can do something like this
Measurement.withDefaultRegion.where( Measurements.name.eq("someName")

Answer 1

I was able to get what I wanted by adding a couple of functions to the model's companion object.
The first one provides the "scope"
fun defaultRegion() :Op<Boolean> {
return Op.build {(exists(Tags.select { Tags.run.eq(Runs.sequelId) and Tags.name.eq("region") and Tags.value.eq("default") })) or notExists(Tags.select {
Tags.run.eq(Runs.sequelId) and Tags.name.eq("region")
})}
}
The second function does the query using the scope and any refinements passed in and returns a "collection" of objects.
fun withDefaultRegionAnd( refinedBy: (SqlExpressionBuilder.()->Op<Boolean>)) : SizedIterable<Measurement> {
return Measurement.wrapRows(Measurements.innerJoin(Runs).select(Measurement.defaultRegion() and SqlExpressionBuilder.refinedBy() ))
}
At the client level I can simply do this:
val measurements = Measurement.withDefaultRegionAnd { Measurements.name.eq("someName") }
Here are the nearly table object and entity classes:
object Measurements : IntIdTable("measurements") {
val sequelId = integer("id").primaryKey()
val run = reference("run_id", Runs)
// more properties
}
class Measurement(id: EntityID<Int>) : IntEntity(id) {
companion object : IntEntityClass<Measurement>(Measurements) {
fun defaultRegion() :Op<Boolean> {
return Op.build {(exists(Tags.select { Tags.run.eq(Runs.sequelId) and Tags.name.eq("region") and Tags.value.eq("default") })) or notExists(Tags.select {
Tags.run.eq(Runs.sequelId) and Tags.name.eq("region")
})}
}
fun withDefaultRegionAnd( refinedBy: (SqlExpressionBuilder.()->Op<Boolean>)) : SizedIterable<Measurement> {
return Measurement.wrapRows(Measurements.innerJoin(Runs).select(Measurement.defaultRegion() and SqlExpressionBuilder.refinedBy() ))
}
}
var run by Run referencedOn Measurements.run
var name by Measurements.name
// more properties
}