allow atoms (interpolated or not) as source in field/2

Author: greg-rychlewski

lib/ecto/query/api.ex

@@ -607,6 +607,10 @@ defmodule Ecto.Query.API do
   query, the two types of names behave the same. However, when referencing
   a field from a schema the behaviours are different.
 
+  The field source can be given as a binding (`p` in `from p in Post`), a
+  late binding (`as/1` and `parent_as/1)` or an atom representing a named
+  binding.
+
   Using an atom to reference a schema field will inherit all the properties from
   the schema. For example, the field name will be changed to the value of `:source`
   before generating the final query and its type behaviour will be dictated by the

lib/ecto/query/builder.ex

@@ -713,12 +713,27 @@ defmodule Ecto.Query.Builder do
     {:{}, [], [dot, [], []]}
   end
 
+  defp escape_field!(source, field, _vars) when is_atom(source) do
+    as = {:{}, [], [:as, [], [source]]}
+    field = quoted_atom_or_string!(field, "field/2")
+    dot = {:{}, [], [:., [], [as, field]]}
+    {:{}, [], [dot, [], []]}
+  end
+
+  defp escape_field!({:^, _, [_]} = expr, field, _vars) do
+    value = quoted_atom!(expr, "field/2")
+    as = {:{}, [], [:as, [], [value]]}
+    field = quoted_atom_or_string!(field, "field/2")
+    dot = {:{}, [], [:., [], [as, field]]}
+    {:{}, [], [dot, [], []]}
+  end
+
   defp escape_field!(expr, field, _vars) do
     error!("""
     cannot fetch field `#{Macro.to_string(field)}` from `#{Macro.to_string(expr)}`. Can only fetch fields from:
 
       * sources, such as `p` in `from p in Post`
-      * named bindings, such as `as(:post)` in `from Post, as: :post`
+      * named bindings, such as `as(:post)` or `:post` in `from Post, as: :post`
       * parent named bindings, such as `parent_as(:post)` in a subquery
     """)
   end
@@ -1376,6 +1391,12 @@ defmodule Ecto.Query.Builder do
     {{:{}, [], [kind, [], [value]]}, field}
   end
 
+  def quoted_type({:field, _, [expr, field]}, _vars)
+      when is_atom(field) or is_binary(field) do
+    source = quoted_atom!(expr, "field/2")
+    {{:{}, [], [:as, [], [source]]}, field}
+  end
+
   # Unquoting code here means the second argument of field will
   # always be unquoted twice, one by the type checking and another
   # in the query itself. We are assuming this is not an issue
@@ -1390,6 +1411,11 @@ defmodule Ecto.Query.Builder do
     {{:{}, [], [kind, [], [value]]}, code}
   end
 
+  def quoted_type({:field, _, [expr, {:^, _, [code]}]}, _vars) do
+    source = quoted_atom!(expr, "field/2")
+    {{:{}, [], [:as, [], [source]]}, code}
+  end
+
   # Interval
   def quoted_type({:datetime_add, _, [_, _, _]}, _vars), do: :naive_datetime
   def quoted_type({:date_add, _, [_, _, _]}, _vars), do: :date

test/ecto/query/builder/select_test.exs

@@ -268,6 +268,9 @@ defmodule Ecto.Query.Builder.SelectTest do
       ref = dynamic(field(as(^as), ^field))
       query = from(b in "blogs", select: ^ref)
 
+      ref = dynamic(field(^as, ^field))
+      query = from(b in "blogs", select: ^ref)
+
       assert Macro.to_string(query.select.expr) == "as(:blog).title()"
     end
 

test/ecto/query/planner_test.exs

@@ -1312,6 +1312,18 @@ defmodule Ecto.Query.PlannerTest do
     assert Macro.to_string(hd(query.wheres).expr) == "&0 . \"visits\"() == ^0"
     assert cast_params == ["123"]
 
+    {query, cast_params, _, _} =
+      from(Post, as: :posts, where: field(^as, :visits) == ^"123") |> normalize_with_params()
+
+    assert Macro.to_string(hd(query.wheres).expr) == "&0.visits() == ^0"
+    assert cast_params == [123]
+
+    {query, cast_params, _, _} =
+      from(Post, as: :posts, where: field(:posts, :visits) == ^"123") |> normalize_with_params()
+
+    assert Macro.to_string(hd(query.wheres).expr) == "&0.visits() == ^0"
+    assert cast_params == [123]
+
     assert_raise Ecto.QueryError, ~r/could not find named binding `as\(:posts\)`/, fn ->
       from(Post, where: as(^as).visits == ^"123") |> normalize()
     end