Fixes exists expressions (#92)

Co-authored-by: Jeff Newman <jmnewm2@localhost.local>

Author: newmanjeff

lib/ecto/adapters/sqlite3/connection.ex

@@ -1340,6 +1340,10 @@ defmodule Ecto.Adapters.SQLite3.Connection do
     ["json_extract(", expr(expr, sources, query), ", '$", path, "')"]
   end
 
+  def expr({:exists, _, [subquery]}, sources, query) do
+    ["exists", expr(subquery, sources, query)]
+  end
+
   def expr({fun, _, args}, sources, query) when is_atom(fun) and is_list(args) do
     {modifier, args} =
       case args do

test/ecto/integration/crud_test.exs

@@ -233,5 +233,16 @@ defmodule Ecto.Integration.CrudTest do
       assert [_] = TestRepo.all(from(a in Account, where: a.email == "hi@hi.com"))
       assert [_] = TestRepo.all(from(a in Account, where: a.email == "HI@HI.COM"))
     end
+
+    test "handles exists subquery" do
+      account1 = TestRepo.insert!(%Account{name: "Main"})
+      user1 = TestRepo.insert!(%User{name: "John"}, [])
+      TestRepo.insert!(%AccountUser{user_id: user1.id, account_id: account1.id})
+
+      subquery =
+        from(au in AccountUser, where: au.user_id == parent_as(:user).id, select: 1)
+
+      assert [_] = TestRepo.all(from(a in Account, as: :user, where: exists(subquery)))
+    end
   end
 end