We then connect to our admin user and grant select, insert, update, and delete privileges on the tables in the db_app_data schema to the db_data_access_layer user. This is so that the PL/SQL packages that we will create soon in db_data_access_layer can manipulate data in the db_app_data tables emp and dept: db_app_data@ORA10G> conn admin/admin Connected. admin@ORA10G> -- need direct privileges on the objects for the procedures to admin@ORA10G> -- work admin@ORA10G> grant select, insert, delete, update on emp to db_data_access_layer; Grant succeeded. admin@ORA10G> grant select, insert, delete, update on dept to db_data_access_layer; Grant succeeded.

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So far in this chapter you have looked at how to do vanilla .NET library design with F#. However, frequently F# programmers are designing libraries that are free to make more sophisticated use of F# and more or less assume that client users are using F# as well. To make the best use of F# in this situation, it is helpful to use functional programming design techniques as part of the library design process. For this reason, we ll next cover what functional programming brings to the table with regard to design methodology.

We now connect to the db_data_access_layer user and create the PL/SQL API for our application. Our simplistic API consists of just two packages. The first package is called manager_pkg and contains code to add a department, hire an employee, raise an employee s salary, and fire an employee. admin@ORA10G> conn db_data_access_layer/db_data_access_layer Connected. db_data_access_layer@ORA10G> create or replace package manager_pkg 2 as

Let s recap the origins of the major programming paradigms from a design perspective: Procedural programming arises from the fundamentally imperative nature of processing devices: microprocessors are state machines that manipulate data using side effects. Object-oriented programming arises from the need to encapsulate and reuse large objects such as those used for GUI applications. Functional programming differs in that it arises from one view of the mathematics of computation. That is, functional programming, in its purest form, is a way of describing computations using constructs that have useful mathematical properties, independent of their implementations. For example, functional programming design methodology places great importance on constructs that are compositional. Let s take a simple example: in F#, we can map a function over a list of lists as follows: open List let map2 f inp = map (map f) inp This is a simple example of the inherent compositionality of generic functions: the expression map f has produced a new function that can in turn be used as the argument to map. Understanding compositionality is the key to understanding much of what goes by the name of functional programming. For example, functional programmers aren t interested in a lack of side effects just for the sake of it instead, they like programs that don t use side effects simply because they tend to be more compositional than those that do. Functional programming often goes further by emphasizing transformations that preserve behavior. For example, we expect to be able to make the following refactorings to our code regardless of the function f or of the values inp, x, or rest:

(just choose View Source from your browser to see what we mean!). Many times we ve written managed code to dynamically generate client-side script using an existing set of script libraries as a base, and added custom data as we generate the code. As an example, you can have interdependent drop-down lists, where the entries in list B depend on the choice users make in list A. Using JavaScript, you can dynamically populate list B when a choice is made in list A, without doing a round trip back to the server. The server-side code can dynamically generate the arrays that are used by the script, driven by a back-end data store. This type of work is very easy to do in a postback, but for users with slow connections, a postback for this type of event (based on focus leaving a control) is very unnatural and interrupts the flow of their work. It s borderline unusable.

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