This helper object is needed to instantiate SparkDialect instances that have multipleSelect enabled.
This is a simple alternative to query re-writing that allows Quill table aliases to be selected
in a away that Spark can understand them.
Quill will represent table variable returns as identifiers e.g.
Query[Foo.join(Query[Bar]).on({case (f,b) => f.id == b.fk}) will become:
select f.*, b.* from Foo f join Bar b on f.id == b.fk
In order for this to work properly all we have to do is change the query to:
select struct(f.*), struct(b.*) from Foo f join Bar b on f.id == b.fk
Since the expression of the f and b identifiers in the query happens inside a tokenizer,
all that is needed for a tokenizer to be able the add the struct part is to introduce a multipleSelect
variable that will guide the expansion. The SparkDialectRecursor has been introduced specifically for this reason.
I.e. so that SparkDialect contexts can be recursively declared with a new multipleSelect value.
Multiple selection enabling typically needs to happen in two instances:
Multiple table aliases are selected as multiple SelectValues. This typically happens when the output of a query is a single tuple with
multiple case classes in it (as is the case with the example above). Or a true nested entity (as these are supported in Spark).
The runSuperAstParser method covers this case.
Multiple table aliases are inside of a single case-class SelectValue. This typically happens when a Ad-Hoc case class is used.
The runCaseClassWithMultipleSelect method covers this case.
This helper object is needed to instantiate SparkDialect instances that have multipleSelect enabled. This is a simple alternative to query re-writing that allows Quill table aliases to be selected in a away that Spark can understand them.
Quill will represent table variable returns as identifiers e.g.
Query[Foo.join(Query[Bar]).on({case (f,b) => f.id == b.fk})will become:
select f.*, b.* from Foo f join Bar b on f.id == b.fkIn order for this to work properly all we have to do is change the query to:select struct(f.*), struct(b.*) from Foo f join Bar b on f.id == b.fkSince the expression of the
fandbidentifiers in the query happens inside a tokenizer, all that is needed for a tokenizer to be able the add thestructpart is to introduce amultipleSelectvariable that will guide the expansion. TheSparkDialectRecursorhas been introduced specifically for this reason. I.e. so that SparkDialect contexts can be recursively declared with a newmultipleSelectvalue.Multiple selection enabling typically needs to happen in two instances:
runSuperAstParsermethod covers this case.runCaseClassWithMultipleSelectmethod covers this case.