From 70abcd534a59143d0dc1f2d544e77dcec609bfbd Mon Sep 17 00:00:00 2001
From: Bart Koelman <bart@degreed.com>
Date: Tue, 18 May 2021 15:45:46 +0200
Subject: [PATCH] Fixes error when using EagerLoad on a relationship

---
 .../Internal/QueryableBuilding/SelectClauseBuilder.cs     | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/JsonApiDotNetCore/Queries/Internal/QueryableBuilding/SelectClauseBuilder.cs b/src/JsonApiDotNetCore/Queries/Internal/QueryableBuilding/SelectClauseBuilder.cs
index b6ddf29c9a..42bf327fdb 100644
--- a/src/JsonApiDotNetCore/Queries/Internal/QueryableBuilding/SelectClauseBuilder.cs
+++ b/src/JsonApiDotNetCore/Queries/Internal/QueryableBuilding/SelectClauseBuilder.cs
@@ -133,6 +133,14 @@ private ICollection<PropertySelector> ToPropertySelectors(IDictionary<ResourceFi
             foreach (EagerLoadAttribute eagerLoad in resourceContext.EagerLoads)
             {
                 var propertySelector = new PropertySelector(eagerLoad.Property);
+
+                // When an entity navigation property is decorated with both EagerLoadAttribute and RelationshipAttribute,
+                // it may already exist with a sub-layer. So do not overwrite in that case.
+                if (!propertySelectors.ContainsKey(propertySelector.Property))
+                {
+                    propertySelectors[propertySelector.Property] = propertySelector;
+                }
+
                 propertySelectors[propertySelector.Property] = propertySelector;
             }