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

Before you start migrating a native project so that you can extend it with managed types, you should consider what impacts this has. Using managed constructs in your project implies that your code depends on the CLR 2.0 at runtime and that the managed code parts are executed under the CLR s control. All services of the CLR can be beneficial if you know how to use them, but if you are not aware of these services, they can also imply pitfalls. For example, CAS may prevent you from running your code via a network share. In most cases, these pitfalls can be avoided (e.g., by modifying the .NET security configuration). Once you have finished these up-front considerations, you should follow the step-by-step instructions described in this chapter to migrate the project. Testing is an essential part of this migration because it allows you to detect scenarios that you have not considered up front. Once the project is migrated, C++/CLI s interoperability features allow you to call managed functions from native functions and vice versa. The functions used so far have had void as a return type, and no arguments. The next chapter covers how and why you can also use complex native types at the migration boundary.

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Note that the AS OF clause is optional, and when you use it, the database will retrieve all the rows as of that particular SCN or time stamp. If the VERSIONS clause is used by itself, as in VERSIONS

Now we create the ed script that will replace the encrypted password string with the CLOSED string.

BETWEEN SCN MINVALUE AND MAXVALUE, without using the optional AS OF clause, the data is retrieved as of the current session. If you add the AS OF clause, as shown next, the data is retrieved as of a specified SCN or clock time: VERSIONS BETWEEN SCN MINVALUE and MAXVALUE AS OF SCN 56789

The output of a Flashback Versions Query is unlike the output of your typical SELECT statement. The output can show multiple versions of the same row, with a row representing each time the particular row was inserted, updated, or deleted. In addition to the column values you specify in the SELECT statement, Oracle will provide you with values for a set of pseudo-columns for each row version. These pseudo-columns provide metadata about the various row versions, including the type of operation, the begin and end time of the transaction, and so on. It is these pseudo-columns that tell you exactly when a row was modified and what was done to the row at that time. Here is a brief explanation of each pseudo-column in the Flashback Versions Query output: VERSIONS_STARTSCN and VERSIONS_STARTTIME: These pseudo-columns tell you the SCN and time stamp when this particular row was first created. If the VERSIONS_STARTTIME is null, the row was created before the lower time boundary of the query. VERSIONS_ENDSCN and VERSIONS_ENDTIME: These pseudo-columns tell you when this particular row expired. If the VERSIONS_ENDTIME column value is null, it means that the row is either current or that it has been deleted. VERSIONS_OPERATION: This pseudo-column provides you with information about the type of DML activity that was performed on the particular row. The column has three possible values: I represents an insert, D a delete operation, and U an update operation. VERSIONS_XID: This pseudo-column displays the unique transaction identifier of the transaction that resulted in this row version.

Note An index-organized table (IOT) will show an update operation as a delete and an insert operation. Your Flashback Versions Query would produce both the deleted and inserted rows as two independent versions. The first version would show a D for the delete operation under the VERSIONS_OPERATION pseudo-column, and the subsequent insert column would show an I for the same pseudo-column.

If the version of a row was created before the MINVALUE or the beginning of the query, you can t capture the value for the starting time stamp or SCN, and your VERSIONS_STARTSCN and VERSIONS_STARTTIME pseudo-columns will be null there won t be any history for this row in your undo segments. The VERSIONS_ENDSCN and VERSIONS_ENDTIME pseudo-columns tell you when the row version expired. If the row version is still current at the time of your Flashback Versions Query, the VERSIONS_ENDSCN and VERSIONS_ENDTIME pseudo-columns will be null. Similarly, if the row version has been deleted from the table, you ll see a null value for these two pseudo-columns.

echo "/$user:$pass_word/s/$pass_word/$CLOSED" > $HOME/$ED echo "w" >> $HOME/$ED echo "q" >> $HOME/$ED

To understand the capabilities and power of the Flashback Versions Query feature, let s look at the simple example shown in Listing 6-1 Listing 6-1 Using the Flashback Versions Query Feature SQL> SELECT versions_xid AS XID, versions_startscn AS START_SCN, versions_endscn AS END_SCN, versions_operation AS OPERATION, empname FROM EMPLOYEES VERSIONS BETWEEN SCN MINVALUE AND MAXVALUE AS OF SCN 7920 WHERE emp_id = 222; XID START_SCN END_SCN OPERATION EMPNAME SALARY ---------------- ---------- --------- ---------- ---------- -----------------0003002F00038BA9 2266 I Nick 19000 0004002D0002B366 0864 D Sam 20000 000400170002B366 0827 0864 I Sam 20000 SQL> The example in Listing 6-1 retrieves three versions of a row for employee number (emp_id) 222 The AS OF SCN of the query is 7920 That is, we want to know what versions of the row existed at this SCN.