WIP: enable hooking into build_assoc functions

Author: bdebinska

lib/predicate_converter.ex

@@ -451,28 +451,38 @@ defmodule Predicates.PredicateConverter do
   defp convert_any({:assoc, field}, sub_predicate, queryable, meta) do
     schema = get_schema(queryable)
 
-    sub_association = get_association_field(schema, field)
-
-    if is_nil(sub_association) do
-      raise PredicateError,
-        message: "Field '#{field}' in schema #{inspect(schema)} is not an association"
-    else
-      parent_table_name = get_table_name(sub_association.owner)
-
-      sub_schema = get_schema(sub_association)
+    subquery =
+      try do
+        subquery = safe_call({schema, :build_assoc}, [field, meta], 1)
 
-      # define the subquery to execute the given predicates against the defined association
-      subquery =
-        from(s in sub_schema,
-          select: 1,
-          where:
-            field(s, ^sub_association.related_key) ==
-              field(parent_as(^parent_table_name), ^sub_association.owner_key)
+        subquery
+        |> where(
+          ^convert_query(subquery, sub_predicate, Map.put(meta, :__nested_virtual_json__, true))
         )
-        |> build_sub_query(sub_predicate, meta)
+      rescue
+        [FunctionClauseError, UndefinedFunctionError] ->
+          sub_association = get_association_field(schema, field)
+
+          if is_nil(sub_association) do
+            raise PredicateError,
+              message: "Field '#{field}' in schema #{inspect(schema)} is not an association"
+          else
+            parent_table_name = get_table_name(sub_association.owner)
+
+            sub_schema = get_schema(sub_association)
+
+            # define the subquery to execute the given predicates against the defined association
+            from(s in sub_schema,
+              select: 1,
+              where:
+                field(s, ^sub_association.related_key) ==
+                  field(parent_as(^parent_table_name), ^sub_association.owner_key)
+            )
+            |> build_sub_query(sub_predicate, meta)
+          end
+      end
 
-      dynamic(exists(subquery))
-    end
+    dynamic(exists(subquery))
   end
 
   defp convert_any({:single, field}, sub_predicate, queryable, meta) do

test/predicates_test.exs

@@ -6,6 +6,29 @@ defmodule PredicatesTest do
   alias Predicates.PredicateConverter, as: Converter
   alias Predicates.PredicateError
 
+  defmodule Prizes do
+    @moduledoc false
+    use Ecto.Schema
+
+    schema "pred_prizes" do
+      field :title, :string
+      field :year, :integer
+
+      belongs_to :author, PredicatesTest.Author
+    end
+
+    def migrate do
+      """
+      CREATE TABLE #{:pred_prizes} (
+        id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
+        title text,
+        year int,
+        author_id int REFERENCES pred_authors(id) ON DELETE CASCADE ON UPDATE CASCADE
+      )
+      """
+    end
+  end
+
   defmodule Post do
     @moduledoc false
     use Ecto.Schema
@@ -62,6 +85,7 @@ defmodule PredicatesTest do
       field :total_tags, {:array, :map}, virtual: true
 
       has_many :posts, Post
+      has_many :prizes, Prizes
     end
 
     def migrate do
@@ -149,14 +173,27 @@ defmodule PredicatesTest do
             }
           )
         )
+
+    def build_assoc(:prizes, meta),
+      do:
+        subquery(
+          from(p in Prizes,
+            where: p.author_id == parent_as(:pred_authors).id,
+            select: %{
+              __element__: fragment("jsonb_build_object('name', ?, 'year', ?)", p.title, p.year)
+            }
+          )
+        )
   end
 
   alias __MODULE__.Author
   alias __MODULE__.Post
+  alias __MODULE__.Prizes
 
   def create_tables(_) do
     Predicates.Repo.query!(Author.migrate(), [])
     Predicates.Repo.query!(Post.migrate(), [])
+    Predicates.Repo.query!(Prizes.migrate(), [])
 
     :ok
   end
@@ -886,6 +923,32 @@ defmodule PredicatesTest do
                )
                |> Predicates.Repo.all()
     end
+
+    test "association with a build_assoc hook" do
+      {2, [hauptmann, _]} =
+        Predicates.Repo.insert_all(Author, [%{name: "Hauptmann"}, %{name: "Schiller"}],
+          returning: true
+        )
+
+      Predicates.Repo.insert_all(Prizes, [
+        %{title: "Nobel Prize", year: 1912, author_id: hauptmann.id}
+      ])
+
+      assert [hauptmann] =
+               Converter.build_query(
+                 Author,
+                 %{
+                   "op" => "any",
+                   "path" => "prizes",
+                   "arg" => %{
+                     "op" => "eq",
+                     "path" => "name",
+                     "arg" => "Nobel Prize"
+                   }
+                 }
+               )
+               |> Predicates.Repo.all()
+    end
   end
 
   describe "conjunctions" do