Merge pull request #179 from gemini-hlsw/topic/avoid-unions-for-singl…

…etons

Performance improvements for singleton sibling lists

modules/sql/src/main/scala/SqlMapping.scala

@@ -580,38 +580,40 @@ trait SqlMapping[F[_]] extends CirceMapping[F] with SqlModule[F] { self =>
 
  /** Does the result of `query` in `context` contain lists of subobjects? */
  def containsNonLeafList(query: Query, context: Context): Boolean = {
- query match {
-
- case Select(fieldName, _, child) =>
- nonLeafList(context, fieldName) ||
- context.forField(fieldName, fieldName).map { fieldContext =>
- containsNonLeafList(child, fieldContext)
+ def loop(query: Query, context: Context, maybe: Boolean): Boolean = {
+ query match {
+ case Select(fieldName, _, child) =>
+ maybe || context.forField(fieldName, fieldName).map { fieldContext =>
+ loop(child, fieldContext, nonLeafList(context, fieldName))
  }.getOrElse(false)
 
- case Group(queries) => queries.exists(q => containsNonLeafList(q, context))
- case GroupList(queries) => queries.exists(q => containsNonLeafList(q, context))
+  case Group(queries) => queries.exists(q => loop(q, context, maybe))
+  case GroupList(queries) => queries.exists(q => loop(q, context, maybe))
 
- case Filter(_, child) => containsNonLeafList(child, context)
- case Unique(child) => containsNonLeafList(child, context)
- case Limit(_, child) => containsNonLeafList(child, context)
- case OrderBy(_, child) => containsNonLeafList(child, context)
+  case Filter(_, child) => loop(child, context, maybe)
+  case Unique(child) => loop(child, context, false)
+  case Limit(n, child) => loop(child, context, maybe && n > 1)
+  case OrderBy(_, child) => loop(child, context, maybe)
 
- case Narrow(_, child) => containsNonLeafList(child, context)
- case Wrap(_, child) => containsNonLeafList(child, context)
- case Rename(_, child) => containsNonLeafList(child, context)
- case _: Count => false
+  case Narrow(_, child) => loop(child, context, maybe)
+  case Wrap(_, child) => loop(child, context, maybe)
+  case Rename(_, child) => loop(child, context, maybe)
+  case _: Count => maybe
 
- case Environment(_, child) => containsNonLeafList(child, context)
+  case Environment(_, child) => loop(child, context, maybe)
 
- case Query.Component(_, _, _) => false
- case _: Introspect => false
- case _: Defer => false
+  case Query.Component(_, _, _) => maybe
+  case _: Introspect => maybe
+  case _: Defer => maybe
 
- case _: Skip => false
- case _: UntypedNarrow => false
- case Skipped => false
- case Empty => false
+ case _: Skip => maybe
+ case _: UntypedNarrow => maybe
+ case Skipped => maybe
+ case Empty => maybe
+ }
  }
+
+ loop(query, context, false)
  }
 
  /** Return the fully aliased column corresponding to the given unaliased columne `cr` in `context` */