From 9b44f6e5ed0a8f165468d4b6b6a21944c9d986f1 Mon Sep 17 00:00:00 2001
From: Jesse Stimpson <jesse.stimpson@gmail.com>
Date: Mon, 13 Apr 2026 20:53:02 -0400
Subject: [PATCH] (#93) Index mapper will now only extract Key tuple items

---
 CHANGELOG.md                             |  8 ++++++++
 lib/ecto_foundationdb/indexer/default.ex | 17 ++++++++++++-----
 mix.exs                                  |  2 +-
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8eb4d7b..36d53eb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## v0.7.4 (2026-04-13)
+
+### Bug fixes
+
+* (#93) Fixed the Mapper used by GetMappedRange, critical for rare cases when the server attempts to fully tuple-decode
+  an Incomplete Versionstamp in the value portion of the Index Entry instead of lazy evaluation. We believe this could
+  cause Error 2042: "The value cannot be parsed as a tuple" in rare cases.
+
 ## v0.7.3 (2026-04-06)
 
 ### Bug fixes
diff --git a/lib/ecto_foundationdb/indexer/default.ex b/lib/ecto_foundationdb/indexer/default.ex
index 46ec712..8273590 100644
--- a/lib/ecto_foundationdb/indexer/default.ex
+++ b/lib/ecto_foundationdb/indexer/default.ex
@@ -186,7 +186,7 @@ defmodule EctoFoundationDB.Indexer.Default do
   # same transaction. So, we must choose either the key or the value of the index entry.
   # A natural choice is to use the value to have the versionstamp so that
   # get_mapped_range works correctly. However, then we lose the ability to manage the index
-  # on updates and clears. Therefore, we must put the versionstamp in the index_key and
+  # on updates and clears. Therefore, we must put the versionstamp in the index_key,
   # which forces our mapper to inspect both the key and value to extract the pk.
   #
   # This means that the value portion of the index kv will always be written with an
@@ -393,18 +393,25 @@ defmodule EctoFoundationDB.Indexer.Default do
     """
   end
 
-  # See key-value design in get_index_entry
   defp mapper(tenant, idx_len) do
+    # (#93) We choose to extract all items from the Key, because when Versionstamps are in play,
+    # the Value is not actually a valid tuple. It contains the incomplete versionstamp, which
+    # which has a short trailing portion. If FDB allowed us to set_versionstamp_key_and_value
+    # then we'd be free to define the mapper on either the key or the value. But since we are
+    # forced to pick set_versionstamped_key, which must also extract the tuple items from the
+    # Key.
+    #
+    # Also see key-value design in get_index_entry and set_index_entry for more details.
     offset_fun = fn offset ->
       [
         # prefix
-        "{V[#{offset}]}",
+        "{K[#{offset}]}",
 
         # source
-        "{V[#{offset + 1}]}",
+        "{K[#{offset + 1}]}",
 
         # namespace
-        "{V[#{offset + 2}]}",
+        "d",
 
         # pk: get it from the index_key because the versionstamp lives there, not in the value
         "{K[#{offset + 5 + idx_len}]}",
diff --git a/mix.exs b/mix.exs
index 22c2ac9..6bb3e0d 100644
--- a/mix.exs
+++ b/mix.exs
@@ -4,7 +4,7 @@ defmodule EctoFoundationdb.MixProject do
   def project do
     [
       app: :ecto_foundationdb,
-      version: "0.7.3",
+      version: "0.7.4",
       description: "FoundationDB adapter for Ecto",
       elixir: "~> 1.15",
       start_permanent: Mix.env() == :prod,