Added support for multi-if in TDS context and test (#4321)

Author: ahallgs

legend-engine-core/legend-engine-core-pure/legend-engine-pure-code-functions-relation/legend-engine-pure-functions-relation-pure/src/main/resources/core_functions_relation/relation/tests/composition.pure

@@ -1324,4 +1324,25 @@ function <<PCT.test, PCTRelationQualifier.relation, PCTCoreQualifier.variant>> m
 Class <<access.private>> meta::pure::functions::relation::tests::composition::Person
 {
   <<equality.Key>> name: String[1];
+}
+
+function <<PCT.test, PCTRelationQualifier.relation>> meta::pure::functions::relation::tests::composition::testMultiIfTDS<T|m>(f:Function<{Function<{->T[m]}>[1]->T[m]}>[1]):Boolean[1]
+{
+  let expr = {
+              | #TDS
+                id, resA, resB
+                1, a, b
+                2, aa, bb
+                3, aaa, bbb
+              #->extend(~val : x | if([pair(|$x.id == 1, |$x.resA), pair(|$x.id == 2, |$x.resB)], |$x.resB));
+            };
+
+   let res =  $f->eval($expr);
+
+  assertEquals('#TDS\n'+
+                '   id,resA,resB,val\n'+
+                '   1,a,b,a\n'+
+                '   2,aa,bb,bb\n'+
+                '   3,aaa,bbb,bbb\n'+
+                '#', $res->sort([~id->ascending()])->toString());
 }

legend-engine-xts-relationalStore/legend-engine-xt-relationalStore-generation/legend-engine-xt-relationalStore-pure/legend-engine-xt-relationalStore-core-pure/src/main/resources/core_relational/relational/pureToSQLQuery/pureToSQLQuery.pure

@@ -6436,7 +6436,7 @@ function <<access.private>> meta::relational::functions::pureToSqlQuery::process
   let paths = $mainQuery.select->cast(@TdsSelectSqlQuery).paths;
 
   // todo this should be the behavior, but just scoping variant to reduce scope of change
-  let newElement = if($expressionToRoute->isVariantInput($vars, $state),
+  let newElement = if($expressionToRoute->isVariantInput($vars, $state) || ($expressionToRoute->instanceOf(FunctionExpression) && $expressionToRoute->cast(@FunctionExpression).func == if_Pair_MANY__Function_1__T_m_),
     |
         let select = $mainQuery.select;
         $expressionToRoute->cast(@FunctionExpression)->processFunctionExpression($currentPropertyMapping, ^$mainQuery(select = ^$select(columns = [], filteringOperation = []), parent = $mainQuery), $vars, $state, $joinType, $nodeId, $aggFromMap, $context->shift(), $extensions)->cast(@OperationWithParentPropertyMapping).element->cast(@SelectWithCursor).select.columns->toOne();,