.NET/Java PDF, Tiff, Barcode SDK Library

.NET delegate types (mentioned briefly in s 5 and 6) Enumerations (that is, enums from languages such as C#; mentioned briefly in 6) Constants (that is, constant literals from languages such as C#) Type parameters (that is, generic parameters; see 5) From the perspective of F# programming, you must also consider the following constructs: Discriminated union types and their tags (s 3 and 9) Record types and their fields ( 3) Type abbreviations ( 3) Values and functions declared using let and let rec ( 3) Modules ( 6) Named arguments ( 6) Optional arguments ( 6) Framework library design is always nontrivial and often underestimated. F# framework and library design methodology is inevitably strongly rooted in the context of .NET object-oriented programming. In this chapter, we give our opinions on how you can go about approaching library design in the context of F# programming. The opinions are neither proscriptive nor official. More official guidelines may be developed by the F# team and community at some future point, though ultimately the final choices lie with F# programmers and software architects.

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Figure 15-2 shows our example application architecture. Application users clerk1 and manager1 map to the database schemas db_clerk1 and db_manager1, respectively. The schema db_data_access_layer consists of PL/SQL code with privileges to manipulate data stored in a third schema called db_app_data. The schema db_clerk1 has the role clerk_role, which can execute the package clerk_pkg. The user db_manager1 has the role manager_role, which can execute the packages clerk_pkg and manager_pkg.

Note Notice that you re using the LosFormatter to serialize your data into the database. This is the

db_manager1 manager_role can execute clerk_pkg and manager _pkg clerk_role can only execute clerk_pkg

Note Some F# programmers choose to use library and coding conventions much more closely associated

Figure 15-2. Our example application architecture Our rather simplistic HR application consists of two PL/SQL packages that allow a user to perform various actions on the emp and dept tables. The package manager_pkg allows a user to add a department, hire an employee, raise a salary, and so on. The package clerk_pkg allows a user to list the employee and department details.

with OCaml, with Python, or with a particular application domain such as hardware verification. For example, OCaml coding uses underscores in names extensively, a practice avoided by the .NET Framework guidelines but used in places by the F# library itself. Some also choose to adjust coding conventions to their personal or team tastes.

limited object serializer formatter. It s like the BinaryFormatter, but is highly optimized for strings, arrays, and hashtables.

The architecture shown in Figure 15-2 illustrates the following: Use of database roles to control end user access to the application functionality: For example, the user db_manager1 has the privileges to execute both packages, manager_pkg and clerk_pkg, via the roles manager_role and clerk_role. However, the user db_clerk1 only needs to report on the data, not modify it, so that user is given the minimum necessary privileges to perform these tasks. This user can execute only clerk_pkg via the role clerk_role. Separation of the data and the application logic that accesses that data into two distinct schemas: The schema db_app_data contains the application objects (the emp and dept tables) and the application data. The schema db_data_access_layer contains the application API to access data in the schema db_app_data. In our example, this API consists of the two PL/SQL packages clerk_pkg and manager_pkg. As discussed earlier, the main advantage of creating two separate schemas for data and the data access layer code is that we can grant only the minimum required privileges on db_app_data objects to the db_data_access_layer schema. For example, as shown in the design in Figure 15-2, the db_data_access_layer schema cannot drop the tables emp and dept. Thus, we uphold the principle of maintaining the least privileges needed to get the job done. Let s go ahead and create all the schema objects from scratch, and then we ll demonstrate how the application actually authenticates to the database in order to perform the requested actions, focusing on the proxy authentication technique.