calasql-core_2.13.0.1.6.source-code.LiveSqlExprs.scala Maven / Gradle / Ivy
package scalasql.core
/**
* Models a set of live [[Expr]] expressions which need to be rendered;
* [[Expr]] expressions not in this set can be skipped during rendering
* to improve the conciseness of the rendered SQL string.
*
* - `None` is used to indicate this is a top-level context and we want
* all expressions to be rendered
*
* - `Some(set)` indicates that only the expressions present in the `set`
* need to be rendered, and the rest can be elided.
*
* Typically downstream parts of a SQL query (e.g. the outer `SELECT`) are
* rendered before the upstream parts (e.g. `FROM (SELECT ...)` subqueries),
* so the [[LiveExprs]] from the downstream parts can be used to decide
* which columns to skip when rendering the upstream parts. The outermost
* `SELECT` is rendered using [[LiveExprs.none]] since we cannot know what
* columns end up being used in the application code after the query has
* finished running, and thus have to preserve all of them
*/
class LiveExprs(val values: Option[Set[Expr.Identity]]) {
def map(f: Set[Expr.Identity] => Set[Expr.Identity]) = new LiveExprs(values.map(f))
def isLive(e: Expr.Identity) = values.fold(true)(_.contains(e))
}
object LiveExprs {
def some(v: Set[Expr.Identity]) = new LiveExprs(Some(v))
def none = new LiveExprs(None)
}