From 8d1e6bc0f8e9710dcba60a1b8e4ec3f47e8bf8ea Mon Sep 17 00:00:00 2001
From: Dmitry Zenovich <dzenovich@gmail.com>
Date: Fri, 19 Apr 2019 14:41:30 +0300
Subject: [PATCH] remove old elements from the output parameter of Pluck()

---
 main_test.go | 31 +++++++++++++++++++++++++++++++
 scope.go     |  4 ++++
 2 files changed, 35 insertions(+)

diff --git a/main_test.go b/main_test.go
index 1dc30093..4100c7f8 100644
--- a/main_test.go
+++ b/main_test.go
@@ -1110,6 +1110,37 @@ func TestCountWithHaving(t *testing.T) {
 	}
 }
 
+func TestPluck(t *testing.T) {
+	db := DB.New()
+	db.Delete(User{})
+	defer db.Delete(User{})
+
+	DB.Create(&User{Id: 1, Name: "user1"})
+	DB.Create(&User{Id: 2, Name: "user2"})
+	DB.Create(&User{Id: 3, Name: "user3"})
+
+	var ids []int64
+	err := db.Model(User{}).Order("id").Pluck("id", &ids).Error
+
+	if err != nil {
+		t.Error("Unexpected error on pluck")
+	}
+
+	if len(ids) != 3 || ids[0] != 1 || ids[1] != 2 || ids[2] != 3 {
+		t.Error("Unexpected result on pluck")
+	}
+
+	err = db.Model(User{}).Order("id").Pluck("id", &ids).Error
+
+	if err != nil {
+		t.Error("Unexpected error on pluck again")
+	}
+
+	if len(ids) != 3 || ids[0] != 1 || ids[1] != 2 || ids[2] != 3 {
+		t.Error("Unexpected result on pluck again")
+	}
+}
+
 func BenchmarkGorm(b *testing.B) {
 	b.N = 2000
 	for x := 0; x < b.N; x++ {
diff --git a/scope.go b/scope.go
index 7fa64b19..0767bb66 100644
--- a/scope.go
+++ b/scope.go
@@ -984,6 +984,10 @@ func (scope *Scope) pluck(column string, value interface{}) *Scope {
 		return scope
 	}
 
+	if dest.Len() > 0 {
+		dest.Set(reflect.Zero(dest.Type()))
+	}
+
 	if query, ok := scope.Search.selects["query"]; !ok || !scope.isQueryForColumn(query, column) {
 		scope.Search.Select(column)
 	}