Embedded Value / Aggregate Mapping

Maps an object into several fields of another object’s table.

• Overview
• How It Works
• When to Use It

Overview

An Embedded Value maps the values of an object to fields in the record of the object’s owner.

Many small objects make sense in an OO system that don’t make sense as tables in a database (e.g. currency-aware money objects and date ranges).

How It Works

• When the owning object is loaded or saved, the dependent objects are loaded and saved at the same time.

• The dependent classes won’t have their own persistence methods since all persistence is done by the owner.

• You can think of Embedded Valueof as a special case of Dependent Mapping, where the value is a single dependent object.

When to Use It

• Simple Value Objects like money and date range.

• When storing reference to dependent objects has no relevance outside the context of the owner (e.g. you only load dependents when loading the owner).

• If mapping to an existing schema and a talbe contains data that you split into more than one object in memory.

• Can only be used for fairly simple dependents. For more complex structures, including potentially large object subgraphs, you should consider Serialized LOB.