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ASP.NET PDF Viewer using C#, VB/NETObviously, given the earlier rules, a query executed in any database using the READ COMMITTED isolation will behave in the same way, will it not It will not If you query multiple rows in a single statement, in almost every other database, READ COMMITTED isolation can be as bad as a dirty read, depending on the implementation In Oracle, using multi-versioning and read-consistent queries, the answer we get from the ACCOUNTS query is the same in READ COMMITTED as it was in the READ UNCOMMITTED example Oracle will reconstruct the modified data as it appeared when the query began, returning the answer that was in the database when the query started Let s now take a look at how our previous example might work in READ COMMITTED mode in other databases you might find the answer surprising. ssrs code 128, ssrs code 39, ssrs data matrix, winforms pdf 417 reader, winforms qr code reader, winforms upc-a reader, itextsharp remove text from pdf c#, itextsharp replace text in pdf c#, winforms ean 13 reader, c# remove text from pdf,We ll pick up our example at the point described in the previous table: We are in the middle of the table We have read and summed the first N rows The other transaction has moved $40000 from account 123 to account 987 The transaction has not yet committed, so rows containing the information for accounts 123 and 987 are locked.. </head> <body> <form id="Form1" runat="server"> <h2>Displaying data</h2> <p> Compute primes from <asp:TextBox runat="server" id="LowerLimit" /> to <asp:TextBox runat="server" id="UpperLimit" />. </p> <asp:Button runat="server" id="GenerateData" text="Generate" OnClick="GenerateData_Click" /> <p> Results: <ul> <asp:Repeater id="Repeater" runat="server"> <ItemTemplate> <li style="color:blue"> n = <%# this.Eval("Item1") %>, time since previous: <%# this.Eval("Item2") %></li> </ItemTemplate> <AlternatingItemTemplate> <li style="color:green"> n = <%# this.Eval("Item1") %>, time since previous: <%# this.Eval("Item2") %></li> </AlternatingItemTemplate> </asp:Repeater> </ul> </p> </form> </body> </html> The application in Listing 14-6 consists of two input controls with the ASP.NET names LowerLimit and UpperLimit and an ASP.NET data-listing control called Repeater. The rest of the code is HTML markup and the F# embedded script to naively compute a sequence of prime numbers in the given range using the F# bigint type. The function isPrime implements the basic naive primality test. The computed value data is a list of tuples containing the prime numbers found in the given range. The type of each entry of this data list is (bigint * System.TimeSpan). This code demonstrates how to acquire input data from forms filled in by the client and how to display data grids back to the client. The input data is acquired simply by using page.LowerLimit.Text and page.UpperLimit.Text in the server-side event handlers. We know what happens in Oracle when it gets to account 987 it will read around the modified data, find out it should be $100.00, and complete. Table 7-4 shows how another database, running in some default READ COMMITTED mode, might arrive at the answer. Table 7-4. Timeline in a Non-Oracle Database Using READ COMMITTED Isolation Reads row 1, account 123, value=$500. Sum=$500.00 so far. Reads row 2, account 456, value=$240.25. Sum=$740.25 so far. -- The data grid is generated by using the Repeater control to iteratively generate HTML; conceptually this is somewhat like a for loop that prints HTML at each step. Here is the relevant snippet: <asp:Repeater id="Repeater" runat="server"> <ItemTemplate> <li style="color:blue"> n = <%# this.Eval("Item1") %>, time since previous: <%# this.Eval("Item2") %></li> </ItemTemplate> <AlternatingItemTemplate> ... </AlternatingItemTemplate> </asp:Repeater> The repeater control contains two templates that define the HTML code that is generated during the iteration. It is common that subsequent lines use different formatting, and Repeater automatically switches between ItemTemplate and AlternatingItemTemplate. The body of the template uses somewhat cryptic ASP.NET constructs such as <%# this.Eval("Item1") %>. These are instances of one of the ASP.NET-embedded F# expression forms from Table 14-3. ASP.NET textually evaluates this element at each step of the repeated iteration. The repeater iterates over a data source. The data source can be specified either declaratively as we will see later or programmatically as in this example using the following lines: page.Repeater.DataSource <- data page.Repeater.DataBind() Updates row 1 (account 123) and puts an exclusive lock on row 1, preventing other updates and reads. Row 1 had $500.00, now it has $100.00. -Updates row 342,023 (account 987) and puts an exclusive lock on this row. This row had $100, now it has $500.00. Reads row N. Sum = . . . -- Figure 14-2. Computing a data table using Listing 14-4 Tries to read row 342,023, account 987. Discovers that it is locked. This session will block and wait for this row's block to become available. All processing on this query stops. -Reads row 342,023, account 987, sees $500.00, and presents a final answer that includes the $400.00 double-counted. Commits transaction. --
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