.NET/ASP.NET/C#/VB.NET PDF Document SDK

With ADO.NET, data is acquired through a connection to the database via a provider. This connection serves as a medium to execute a command against; this can be used to fetch, update, insert, or delete data from the data store. Statements and queries are articulated as SQL text (CREATE, SELECT, UPDATE, INSERT, and DELETE statements) and are passed to the command object s constructor. When you execute these statements, you obtain data (in the case of queries) or the number of affected rows (in the case of UPDATE, INSERT, or DELETE statements). The data returned can be processed via two main mechanisms: sequentially in a read-only fashion using a DataReader object or by loading it into an in-memory representation (a DataSet object) for further disconnected processing. DataSet objects store data in a set of table objects and along with them metadata that describes their relationships and constraints in a fully contained model. ADO.NET 2.0 comes with four data providers: SQLClient, OleDb, Oracle, and Odbc. Table 16-2 describes them and a couple of more commonly used providers. These providers act as the main gateway to the database.

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into the code, and enables you to simply decorate your types with declarations of their security requirements. You use the SecurityRole attribute for this purpose as well. (This code is in the Serviced project of the Code07 solution.) [SecurityRole("Manager")] public class RBDemo { public RBDemo() {} public DataSet GetManagerData() { //implementation return new DataSet(); } [SecurityRole("Executuve")] public DataSet GetExecutiveData() { //implementation return new DataSet(); } } In this class, callers to any method must be in the Manager role. You ve further restrained access to the GetExecutiveData method, requiring that callers to that method are in the Executive role. You could also apply the attribute to an interface declaration. Sometimes you need a finer grain of control over your role-based security implementation. For example, you may want to render a list of reports, and user roles determine access to the reports. In these cases, you ll need programmatic access to the roles information. This is exposed to use via the SecurityCallContext type. While this may at first appear to be similar to ContextUtil, security context is different, so using SecurityCallContext is required in this case. public void GetReportData(DataSet reportCriteriaData) { // Get the current security call context SecurityCallContext callCtx = SecurityCallContext.CurrentCall; // Verify role based security is enabled (optional) if (callCtx.IsSecurityEnabled) { // Only allow managers to generate reports if (callCtx.IsCallerInRole("Manager")) { // proceed with report generation } else {

> let plusExpr = <@ 1 + 1 @>;; val plusExpr : Expr<int> > plusExpr;; val it : Expr<int> = <@ Microsoft.FSharp.Core.Operators.op_Addition (Int32 1) (Int32 1) @> You can see here that the act of quoting an expression gives you the expression back as data. Those familiar with Lisp or Scheme will know a version of this in the form of Lisp quotations, and those familiar with C# 3.0 will find it familiar, since C# uses similar mechanisms for its lambda expressions. F# quotations are distinctive partly because they are typed (like C# lambda expressions) and because the functional, expression-based nature of F# means that so much of the language can be quoted and manipulated relatively easily. We use quotations in only a few places in this book. In 15, we utilize an F# library that converts F# quotations to SQL via the .NET LINQ library. The essence of the way this converter works is summarized by the following type:

6 2 19 9 4 21 0 0 7 0 0 7

This function effectively acts as an evaluator for quotations. It will successfully evaluate only a limited range of quotations (a runtime error may occur if the expression can t be converted to SQL). Another application of quotations is to convert F# code to JavaScript to let you run it in web browsers. This technique is used by the F# Web Tools, described in 14. This might be implemented by a function with a type such as the following:

// security error } } } Using imperative coding enables you to introduce different flow-of-control scenarios into your code based on the role of your calling users.

From the information in Table 11-2, we can make the following observations: Auto-buffering seems to make a tremendous difference. Notice how the elapsed time is 0 milliseconds (approximately) for the case of getArray() and getOracleArray() when auto-buffering is turned on. Remember, though, that this performance improvement comes at the cost of increased memory consumption. Auto-indexing does not seem to make a lot of difference. In fact, when it is turned on, performance goes down slightly (see rows 4 to 6 as compared to rows 1 to 3 in Table 11-2). This is presumably because of the overhead of creating the index structure when autoindexing is turned on. getArray() and getOracleArray() fare better in general, as compared to getResultSet() (presumably because of the overhead in creating and destroying the ResultSet data structure). With those observations, we conclude our discussions on collections. In the next section, we ll walk through an introduction to references and examine how to access and manipulate references using the JDBC API.