Fix create duplicated constraint, close #4090

schema/relationship.go

@@ -512,6 +512,24 @@ func (rel *Relationship) ParseConstraint() *Constraint {
 		return nil
 	}
 
+	if rel.Type == BelongsTo {
+		for _, r := range rel.FieldSchema.Relationships.Relations {
+			if 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 &&
+						rel.References[idx].PrimaryValue == ref.PrimaryValue) {
+						matched = false
+					}
+				}
+
+				if matched {
+					return nil
+				}
+			}
+		}
+	}
+
 	var (
 		name     string
 		idx      = strings.Index(str, ",")