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.NET/ASP.NET/C#/VB.NET PDF Document SDKYou can use option values for both data and control; they re often used to represent the success or failure of a computation. This can be useful when catching an exception, as shown in the following sample (this sample uses the function http from 2): let fetch url = try Some(http(url)) with : System.Net.WebException -> None We describe exceptions in more detail in 4 what matters here is that if a network error occurs during the HTTP request, then the exception will be caught, and the result of the fetch function will be the value None. Successful web page requests will return a Some value. Option values can then be discriminated and decomposed using pattern matching, as shown here: > match (fetch "http://www.nature.com") with | Some(text) -> printfn "text = %s" text | None -> printfn "**** no web page found";; text = <HTML> ... </HTML> (note: the HTML is shown here if connected to the web) val it : unit = () ssrs code 128 barcode font, ssrs code 39, ssrs data matrix, winforms pdf 417 reader, winforms qr code reader, winforms upc-a reader, c# remove text from pdf, itextsharp replace text in pdf c#, winforms ean 13 reader, itextsharp remove text from pdf c#,new setting, exitcommit. This setting controls whether SQL*Plus issues a COMMIT or ROLLBACK upon exit. So when you use 11g Release 2, the default behavior that has been in place since SQL*Plus was invented may well be different! Transactions are atomic in Oracle, meaning that either every statement that comprises the transaction is committed (made permanent) or all of the statements are rolled back This protection is extended to individual statements as well Either a statement entirely succeeds or the statement is entirely rolled back Note that I said the statement is rolled back The failure of one statement does not cause previously executed statements to be automatically rolled back Their work is preserved and must either be committed or rolled back by you Before we get into the details of exactly what it means for a statement and transaction to be atomic, let s take a look at the various transaction control statements available to us: COMMIT: To use this statement s simplest form, you just issue COMMIT You could be more verbose and say COMMIT WORK, but the two are equivalent. A basic control construct in F# programming is if/then/elif/else. Here s an example: let round x = if x >= 100 then 100 elif x < 0 then 0 else x Conditionals are really shorthand for pattern matching; for example, the previous code could have been written like this: let round x = match x with | _ when x >= 100 -> 100 | _ when x < 0 -> 0 | _ -> x Conditionals are always guarded by a Boolean-valued expression. You can build them using && and || (the and and or operators) as well as any library functions that return Boolean values: let round2 (x,y) = if x >= 100 || y >= 100 then 100,100 elif x < 0 || y < 0 then 0,0 else x,y A COMMIT ends your transaction and makes any changes permanent (durable) There are extensions to the COMMIT statement used in distributed transactions that allow you to label a COMMIT (label a transaction) with some meaningful comment and force the commit of an in-doubt distributed transaction There are also extensions that allow you to perform an asynchronous commit a commit that actually breaks the durability concept We ll take a look at this in a bit and see when it might be appropriate to use ROLLBACK: To use this statement s simplest form, you just issue ROLLBACK Again, you could be more verbose and say ROLLBACK WORK, but the two are equivalent A rollback ends your transaction and undoes any uncommitted changes. It does this by reading information stored in the rollback/undo segments (going forward I ll refer to these exclusively as undo segments, the favored terminology for Oracle 10g and later) and restoring the database blocks to the state they were before your transaction began SAVEPOINT: A SAVEPOINT allows you to create a marked point within a transaction You may have multiple SAVEPOINTs within a single transaction.. The operators && and || have the usual shortcut behavior in that the second argument of && is evaluated only if the first evaluates to true, and likewise, the second argument of || is evaluated only if the first evaluates to false.
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