In Domain-Driven Design (DDD), an aggregate is a cluster of domain objects that are treated as a single unit for the purpose of data changes. The aggregate has a root and a boundary:
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Aggregate Root: This is a single, specific entity that acts as the primary point of interaction. It guarantees the consistency of changes being made within the aggregate by controlling access to its components. The aggregate root enforces all business rules and invariants within the aggregate boundary.
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Boundary: The boundary defines what is inside the aggregate and what is not. It includes the aggregate root and other entities or value objects that are controlled by the root. Changes to entities or value objects within the boundary must go through the aggregate root to ensure consistency.
An example of an aggregate is an Order(which is the Aggregate root) together with OrderItems(entities inside the Aggregate).
The primary function of an aggregate is to ensure data consistency. All invariants are maintained within this boundary.Therefore it is important that when you fetch an aggregate in your application code, that the full aggregate is loaded into memory.
One way to achieve this in EF Core is by taking advantage of the AutoInclude functionality. This allows us to include related data every time an entity is loaded from the database.
If we apply this to the Order example above, the mapping logic would look like this:
if we now fetch the Orders, all OrderItems will be includes as well.
Remark:If we don’t want to load the related data it is still possible by using the IgnoreAutoIncludes method:
More information
Eager Loading of Related Data - EF Core | Microsoft Learn