In Domain-Driven Design (DDD), a Specification is a design pattern used to encapsulate a piece of domain knowledge into a single unit, called a specification. This pattern is particularly useful for defining criteria that domain objects must meet, and it allows for the reuse of these criteria across different parts of the application.
Key Points about the Specification Pattern in DDD:
Encapsulation of Domain Knowledge:
The Specification pattern encapsulates business rules and criteria into a single, reusable unit. This helps in maintaining a clear separation of concerns and keeps the domain model clean and focused on its primary responsibilities[1][2][3].
Use Cases:
Data Retrieval: Specifications can be used to query objects from a database that meet certain criteria.
In-Memory Validation: They can validate that an object in memory meets specific criteria.
Creation of New Objects: Specifications can be used to create new objects that meet certain criteria.
Bulk Updates: They can modify a group of objects that meet certain criteria[2][4][6].
Implementation Strategies:
Hardcoded Specification: Implements the specification as a code fragment, treating it as a strategy. This approach is flexible but requires programming for each new specification.
Parameterized Specification: Allows new specifications to be built without programming, often at runtime, but is limited by the parameters set by the programmers.
Composite Specification: Uses an interpreter to combine basic elements of specifications, providing flexibility and ease of use[3].
Domain Model Purity and Encapsulation:
The Specification pattern can sometimes conflict with principles like domain model purity and persistence ignorance. For example, using specifications for data retrieval and bulk updates can introduce depend...
