.NET/Java PDF, Tiff, Barcode SDK Library

Database connections are precious resources, and you should always release them as soon as possible. In the previous case, we did this by using a locally defined connection. It is also sufficient to implicitly close the reader by constructing it with the CloseConnection option that causes it to release and close the data connection upon closing the reader instance. Further, common options include SchemaOnly that you can use to extract field information only (without any data returned), SingleResult to extract a single value only (the same as using the ExecuteScalar method discussed earlier), SingleRow to extract a single row, and KeyInfo to extract additional columns (appended to the end of the selected ones) automatically that uniquely identify the rows returned.

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2 insert into t values ( 'Anonymous Block' ); 3 Autonomous_Insert; 4 rollback; 5 end; 6 / PL/SQL procedure successfully completed. ops$tkyte%ORA11GR2> select * from t; MSG ------------------------Autonomous Insert Here, only the work done by and committed in the autonomous transaction persists. The INSERT done in the anonymous block was rolled back by the ROLLBACK statement on line 4. The autonomous transaction procedure s COMMIT has no effect on the parent transaction started in the anonymous block. In a nutshell, this captures the essence of autonomous transactions and what they do. To summarize, if you COMMIT inside a normal procedure, it will make durable not only its own work but also any outstanding work performed in that session. However, a COMMIT performed in a procedure with an autonomous transaction will make durable only that procedure s work.

The Oracle database has supported autonomous transactions internally for quite a while We see them all of the time in the form of recursive SQL For example, a recursive transaction may be performed when selecting from a sequence, in order for you to increment the sequence immediately in the SYSSEQ$ table The update of the SYSSEQ$ table in support of your sequence is immediately committed and visible to other transactions, but your transaction is not yet committed Additionally, if you roll back your transaction, the increment to the sequence remains in place; it is not rolled back with your transaction, as it has already been committed Space management, auditing, and other internal operations are performed in a similar recursive fashion This feature has now been exposed for all to use However, I have found that the legitimate realworld use of autonomous transactions is very limited.

Datasets allow applications to work in a so-called disconnected mode, which means the application connects to the database, loads relevant data to an in-memory representation, and processes the data locally. When the processing is completed, the data in the in-memory dataset can be synchronized with the database. ADO.NET datasets are compact in-memory databases and provide similar functionality to real databases; however, they are designed to work with a limited amount of data. A DataSet contains a collection of tables, the relationships between those tables, and various constraints. Tables are represented by the DataTable type. And like in a SQL server, tables are defined by their columns (DataColumn objects), and the data is stored in rows (DataRow objects). In ADO.NET, the loading of data to the dataset and the synchronization to the database are coordinated by data adapters, for instance, SqlDataAdapter objects. Consider the following example in which we define a buildDataSet function that takes a connection and a SQL SELECT query and returns the resulting DataSet object:

Time after time, I see them used as a workaround to such problems as a mutating table constraint in a trigger This almost always leads to data integrity issues, however, since the cause of the mutating table is an attempt to read the table upon which the trigger is firing Well, by using an autonomous transaction you can query the table, but you are querying the table now without being able to see your changes (which is what the mutating table constraint was trying to do in the first place; the table is in the middle of a modification, so query results would be inconsistent) Any decisions you make based on a query from that trigger would be questionable you are reading old data at that point in time A potentially valid use for an autonomous transaction is in custom auditing, but I stress the words potentially valid.