fix diff round-trip comparison

pkg/readers/dbml/reader.go

@@ -571,6 +571,28 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 		}
 	}
 
+	// PostgreSQL readers derive relationships from foreign keys. Do the same
+	// for DBML refs so diffing equivalent schemas compares the same model.
+	for _, schema := range schemaMap {
+		for _, table := range schema.Tables {
+			for _, constraint := range table.Constraints {
+				if constraint.Type != models.ForeignKeyConstraint {
+					continue
+				}
+				name := fmt.Sprintf("%s_to_%s", table.Name, constraint.ReferencedTable)
+				relationship := models.InitRelationship(name, models.OneToMany)
+				relationship.FromTable = table.Name
+				relationship.FromSchema = table.Schema
+				relationship.FromColumns = append([]string(nil), constraint.Columns...)
+				relationship.ToTable = constraint.ReferencedTable
+				relationship.ToSchema = constraint.ReferencedSchema
+				relationship.ToColumns = append([]string(nil), constraint.ReferencedColumns...)
+				relationship.ForeignKey = constraint.Name
+				table.Relationships[name] = relationship
+			}
+		}
+	}
+
 	// Add schemas to database
 	for _, schema := range schemaMap {
 		db.Schemas = append(db.Schemas, schema)