Fix self-referential belongs to constraint (#4801)

* create tests for self-ref has one migration

* add relation equality check to avoid skipping self-referential schemas

* remove drop table error check

schema/relationship.go

@@ -519,7 +519,7 @@ func (rel *Relationship) ParseConstraint() *Constraint {
 
 	if rel.Type == BelongsTo {
 		for _, r := range rel.FieldSchema.Relationships.Relations {
-			if r.FieldSchema == rel.Schema && len(rel.References) == len(r.References) {
+			if r != rel && r.FieldSchema == rel.Schema && len(rel.References) == len(r.References) {
 				matched := true
 				for idx, ref := range r.References {
 					if !(rel.References[idx].PrimaryKey == ref.PrimaryKey && rel.References[idx].ForeignKey == ref.ForeignKey &&

schema/relationship_test.go

@@ -93,6 +93,21 @@ func TestBelongsToWithOnlyReferences2(t *testing.T) {
 	})
 }
 
+func TestSelfReferentialBelongsTo(t *testing.T) {
+	type User struct {
+		ID        int32 `gorm:"primaryKey"`
+		Name      string
+		CreatorID *int32
+		Creator   *User
+	}
+
+	checkStructRelation(t, &User{}, Relation{
+		Name: "Creator", Type: schema.BelongsTo, Schema: "User", FieldSchema: "User",
+		References: []Reference{{"ID", "User", "CreatorID", "User", "", false}},
+	})
+
+}
+
 func TestSelfReferentialBelongsToOverrideReferences(t *testing.T) {
 	type User struct {
 		ID        int32 `gorm:"primaryKey"`

tests/migrate_test.go

@@ -54,6 +54,25 @@ func TestMigrate(t *testing.T) {
 	}
 }
 
+func TestAutoMigrateSelfReferential(t *testing.T) {
+	type MigratePerson struct {
+		ID        uint
+		Name      string
+		ManagerID *uint
+		Manager   *MigratePerson
+	}
+
+	DB.Migrator().DropTable(&MigratePerson{})
+
+	if err := DB.AutoMigrate(&MigratePerson{}); err != nil {
+		t.Fatalf("Failed to auto migrate, but got error %v", err)
+	}
+
+	if !DB.Migrator().HasConstraint("migrate_people", "fk_migrate_people_manager") {
+		t.Fatalf("Failed to find has one constraint between people and managers")
+	}
+}
+
 func TestSmartMigrateColumn(t *testing.T) {
 	fullSupported := map[string]bool{"mysql": true, "postgres": true}[DB.Dialector.Name()]