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Introduction of lambda expression and predicate builder

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  • 1. Introduction of Lambda Expression and Predicate Builder Bryan lin 2014/03/07
  • 2. Agenda • Lambda Expression • PredicateBuilder • Implementation of PredicateBuilder
  • 3. Lambda expression • What is a Lambda Expression? • A lambda expression is an anonymous function and it is mostly used to create delegates in LINQ. Simply put, it's a method without a declaration, i.e., access modifier, return value declaration, and name.
  • 4. Lambda expression • Why do we need lambda expressions? (Why would we need to write a method without a name?) • Convenience. It's a shorthand that allows you to write a method in the same place you are going to use it. Especially useful in places where a method is being used only once, and the method definition is short. It saves you the effort of declaring and writing a separate method to the containing class.
  • 5. Lambda expression • Benefits: • Reduced typing. No need to specify the name of the function, its return type, and its access modifier. • When reading the code you don't need to look elsewhere for the method's definition.
  • 6. Lambda expression • Lambda expressions should be short. A complex definition makes the calling code difficult to read.
  • 7. Lambda expression • How do we define a lambda expression? • Lambda basic definition: Parameters => Executed code.
  • 8. PredicateBuilder • Background • Dynamic Predicate Construction • You allow the user to pick, from a check box list, any of the fields that will be included in the query, and to specify the criteria
  • 9. PredicateBuilder
  • 10. PredicateBuilder • Background • Dynamic Predicate Construction • You can do a bunch of switch-ing if logic to figure out what kind of query to render by adding a piece of it at a time • Or you can use lambdas and the PredicateBuilder to inject multiple predicates into an expression tree
  • 11. PredicateBuilder • Using the Code • To combine the two criteria below:
  • 12. PredicateBuilder • Using the Code • Do with the PredcateBuilder:
  • 13. PredicateBuilder • Using the Code • And then:
  • 14. Implementation of PredicateBuilder • Implmentation of and logic:
  • 15. Implementation of PredicateBuilder • Implementation of or logic:
  • 16. References • http://www.codeproject.com/Tips/298963/Understand-Lambda- Expressions-in-3-minutes • http://www.codeproject.com/Articles/28580/LINQ-and-Dynamic- Predicate-Construction-at-Runtime • http://www.albahari.com/nutshell/predicatebuilder.aspx
  • 17. FAQ