feat: query children of a query

Author: fahchen

lib/query/children.ex

@@ -7,6 +7,23 @@ defmodule Hierarch.Query.Children do
 
     * `:with_self` - when true to include itself. Defaults to false.
   """
+  def query(%{from: %{source: {_table_name, schema}}} = queryable) do
+    path_column = schema.__hierarch__(:path_column)
+
+    [pk_column] = schema.__schema__(:primary_key)
+
+    uuids_query =
+      from t in queryable,
+      select: %{__ancestry__: fragment("text2ltree(replace(ltree2text(?), '-', '_')) || replace(text(?), '-', '_')", field(t, ^path_column), field(t, ^pk_column))}
+
+    uuids_array_query =
+      from t in subquery(uuids_query),
+      select: %{__ltrees__: fragment("array_agg(?)", t.__ancestry__)}
+
+    schema
+    |> join(:cross, [], a in subquery(uuids_array_query))
+    |> where([t, a], field(t, ^path_column) in a.__ltrees__)
+  end
   def query(%schema{} = struct, opts \\ []) do
     with_self = Keyword.get(opts, :with_self, false)
 

test/hierarch/children_test.exs

@@ -53,4 +53,29 @@ defmodule Hierarch.ChildrenTest do
       assert children == [astronomy]
     end
   end
+
+  describe "children/1" do
+    import Ecto.Query
+
+    test "returns children of a query", catelogs do
+      science = Map.get(catelogs, "Top.Science")
+      hobbies   = Map.get(catelogs, "Top.Hobbies")
+
+      astronomy = Map.get(catelogs, "Top.Science.Astronomy")
+
+      amateurs_astronomy = Map.get(catelogs, "Top.Hobbies.Amateurs_Astronomy")
+
+      query = from(
+        c in Catelog,
+        where: c.id in ^[science.id, hobbies.id]
+      )
+
+      descendants =
+        query
+        |> Hierarch.Query.Children.query()
+        |> Repo.all
+
+      assert_match descendants, [astronomy, amateurs_astronomy]
+    end
+  end
 end