From b3d9e9568d614e478247dcdc9ab853a842eb282d Mon Sep 17 00:00:00 2001
From: Rubens Cordeiro <rubens.cordeiro@live.com>
Date: Sat, 8 Mar 2025 16:03:10 +0100
Subject: [PATCH] Improve error message when duplicate enum definitions are
 registered.

---
 .../Storage/Internal/NpgsqlTypeMappingSource.cs          | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/EFCore.PG/Storage/Internal/NpgsqlTypeMappingSource.cs b/src/EFCore.PG/Storage/Internal/NpgsqlTypeMappingSource.cs
index e5719e76e..1a4a8b04c 100644
--- a/src/EFCore.PG/Storage/Internal/NpgsqlTypeMappingSource.cs
+++ b/src/EFCore.PG/Storage/Internal/NpgsqlTypeMappingSource.cs
@@ -785,7 +785,14 @@ static Type FindTypeToInstantiate(Type collectionType, Type elementType)
         EnumDefinition? enumDefinition;
         if (storeType is null)
         {
-            enumDefinition = _enumDefinitions.SingleOrDefault(m => m.ClrType == clrType);
+            var matches = _enumDefinitions.Where(m => m.ClrType == clrType).ToList();
+            if (matches.Count > 1)
+            {
+                throw new InvalidOperationException(
+                    $"Multiple enum definitions registered for CLR type '{clrType?.FullName}'. ");
+            }
+
+            enumDefinition = matches.FirstOrDefault();
 
             if (enumDefinition is null)
             {