Scala Slick: Getting number of fields with a specific value in a group by query - scala

Question

I have a table like this:
|``````````````````````````|
|imgId, pageId, isAnnotated|
|1, 1, true |
|2, 1, false |
|3, 2, true |
|4, 1, false |
|5, 3, false |
|6, 2, true |
|7, 3, true |
|8, 3, true |
|__________________________|
I want the result as:
|`````````````````````````````````````|
|pageId, imageCount, noOfAnotatedImage|
| 1 3 1 |
| 2 2 2 |
| 3 3 2 |
|_____________________________________|
I want the number of annotated images based on number field set as true.
Slick related code I tried which fired exception:
def get = {
val q = (for {
c <- WebImage.webimage
} yield (c.pageUrl, c.lastAccess, c.isAnnotated)).groupBy(a => (a._1, a._3)).map{
case(a,b) => (a._1, b.map(_._2).max, b.filter(_._3 === true).length, b.length)
}
db.run(q.result)
}
Exception:
[SlickTreeException: Cannot convert node to SQL Comprehension
| Path s6._2 : Vector[t2<{s3: String', s4: Long', s5: Boolean'}>]
]
Note: This Count the total records containing specific values thread clear shows that in plain SQL what I need is possible.
SELECT
Type
,sum(case Authorization when 'Accepted' then 1 else 0 end) Accepted
,sum(case Authorization when 'Denied' then 1 else 0 end) Denied
from MyTable
where Type = 'RAID'
group by Type
Changed the code but still getting exception:
Execution exception
[SlickException: No type for symbol s2 found for Ref s2]
In /home/ravinder/IdeaProjects/structurer/app/scrapper/Datastore.scala:60
56 def get = {
57 val q = (for {
58 c <- WebImage.webimage
59 } yield (c.pageUrl, c.lastAccess, c.isAnnotated)).groupBy(a => (a._1, a._3)).map{
[60] case(a,b) => (a._1, b.map(_._2).max, b.map(a => if (a._3.result == true) 1 else 0 ).sum, b.length)
61 }
62 db.run(q.result)
63 }
64

Answer 1

Given your requirement, you should group by only pageUrl so as to perform aggregation over all rows for the same page. You can aggregate lastAccess using max and isAnnotated using sum over a conditional Case.If-Then-Else. The Slick query should look something like the following:
val q = (for {
c <- WebImage.webimage
} yield (c.pageUrl, c.lastAccess, c.isAnnotated)).
groupBy( _._1 ).map{ case (url, grp) =>
val lastAcc = grp.map( _._2 ).max
val annoCnt = grp.map( _._3 ).map(
anno => Case.If(anno === true).Then(1).Else(0)
).sum
(url, lastAcc, annoCnt, , grp.length)
}