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Specification Pattern

  • Specification pattern make business rules in chain with boolean result set. Write intention.

Use Specification Pattern

  • Specify criteria for selection
  • In-memory validation
  • Retrieving data - like filtering

Specification -- Is Satisfied By --> Object

Benefits of the Specification Pattern

  • Reduced coupling - Decoupling
  • Separation of Concerns
  • Avoiding domain knowledge duplication (DRY)
  • Easier to test
Related Patterns
  • Factory

Rules can use Func<T, bool> or Expression<Func<T,bool>>

Sample Boolean expression

Func<Song, bool> topSongsPredicate = s => s.Rating > 4;
data.Songs.Where(topSongsPredicate);

Expression<Func<Song, bool>> topSongsExpression = s => s.Rating > 4;
data.Songs.Where(topSongsExpression.Compile());

// Reason why use expession instead of predicate. you can pass around an expression, 
// you can edit that expression and build upon it

Example: s => s.Rating > 3