Slick: Dynamic query conditions using the **MaybeFilter** (Updated to support nullable columns)

gistfile1.scala

import scala.slick.lifted.CanBeQueryCondition
// optionally filter on a column with a supplied predicate
case class MaybeFilter[X, Y](val query: scala.slick.lifted.Query[X, Y]) {
  def filter[T,R:CanBeQueryCondition](data: Option[T])(f: T => X => R) = {
    data.map(v => MaybeFilter(query.filter(f(v)))).getOrElse(this)
  }
}

// example use case
import java.sql.Date
class SomeTable(tag: Tag) extends Table[(Int, Date, Date)](tag, "some_table") {
  def id = column[Int]("id", O.PrimaryKey, O.AutoInc)
  def created = column[Date]("created")
  def modified = column[Date]("modified")
  def * = (id, created, modified)
}
lazy val someTable = TableQuery[SomeTable]
someTable.ddl.create

def find(id: Option[Int], createdMin: Option[Date], createdMax: Option[Date], modifiedMin: Option[Date], modifiedMax: Option[Date]) = {
  MaybeFilter(someTable)
    .filter(id)(v => d => d.id === v)
    .filter(createdMin)(v => d => d.created >= v)
    .filter(createdMax)(v => d => d.created <= v)
    .filter(modifiedMin)(v => d => d.modified >= v)
    .filter(modifiedMax)(v => d => d.modified <= v)           
    .query
}
find(Some(1),None,None,None,None).list // <- example: find by id only

@simao, this fails on:

table.maybeFilter(_.someColumn.asColumnOf[String] like arg.map(a => s"%$a%)).take(10).result

at least on mariadb it looks like it generates invalid query in the end:

Query is: select `id`, `some_column`, `status` from `test_table` where ifnull((convert(`some_column`,VARCHAR)) like '%test%',true) limit 10

Do you know what is this ifnull? - update: ifnull is db function to filter expressions

without maybeFilter it does not work either, but that is another story :)

update: problem is related to slick, as it can't do like query on field with custom mapping. once column type is plain String, it all works

how to make it happen on Slick 1.0.0?

Very useful, thank you!