From 1c354b33b71f74931299aeed4e2bd71c62c2d0f3 Mon Sep 17 00:00:00 2001
From: Rebecca Le <rebecca@alembic.com.au>
Date: Mon, 12 Oct 2020 09:50:51 +0800
Subject: [PATCH] Use the same database prefix as the existing rows when
 preloading via a lateral join

---
 lib/dataloader/ecto.ex | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/dataloader/ecto.ex b/lib/dataloader/ecto.ex
index 0f3901e..bc4e14f 100644
--- a/lib/dataloader/ecto.ex
+++ b/lib/dataloader/ecto.ex
@@ -673,9 +673,12 @@ if Code.ensure_loaded?(Ecto) do
 
       def preload_lateral([], _assoc, _query, _opts), do: []
 
-      def preload_lateral([%schema{} | _] = structs, assoc, query, repo, repo_opts) do
+      def preload_lateral([%schema{} = struct | _] = structs, assoc, query, repo, repo_opts) do
         [pk] = schema.__schema__(:primary_key)
 
+        # Carry the database prefix across from already-loaded records if not already set
+        repo_opts = Keyword.put_new(repo_opts, :prefix, struct.__meta__.prefix)
+
         assocs = expand_assocs(schema, [assoc])
 
         inner_query =