Using a scrollable and updateable JDBC ResultSet. in Java

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Listing 3.8 Using a scrollable and updateable JDBC ResultSet.
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_SENSITIVE. If the type is forward-only, the result set is not scrollable and not sensitive to updates (JDBC 1.0 functionality). A scroll-sensitive result set is both scrollable and sensitive to changes in the underlying column values, and the scroll-insensitive result set is scrollable but not sensitive to changes once the query is executed. The concurrency type of the result set. This parameter determines whether the result set can be used to perform updates, including inserting new rows or deleting existing rows. It can have one of two static constant values defined in the java.sql.ResultSet class: java.sql.ResultSet.CONCUR_READ_ONLY, java.sql .ResultSet.CONCUR_UPDATABLE. A read-only result set does not allow data in the rows to be modified. For an updateable result set, updates, inserts, and deletes can be performed on the rows in the result set and copied to the database. Coming back to the example in Listing 3.8, once the JDBC statement has been created with the desired scrollability/sensitivity type, the query can be executed in the
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usual way. This creates a result set of the specified type, which in our example is scrollinsensitive and updateable. Let us assume that we just want to update the last row in the result set. In this case the scrollable result set is positioned to the last row by calling the last() method for absolute positioning. The data in this row is then modified through updateXXX() calls (available only for updateable result sets) that change the column values, where XXX stands for the column type such as String or Int. Each of these updateXXX() methods takes two arguments: an integer value denoting the column number or a string for the column name, and then the new value of the appropriate type. After all the columns have been updated, in our case the phone number and address, the updateRow() method is called to copy the changes to the database. These changes are made permanent with the next COMMIT operation. The changes can be undone and the columns reverted to their original data values by calling the cancelRowUpdates() method instead of updateRow(). SQLJ Iterators versus JDBC ResultSets Now that we have learned about both SQLJ iterators and JDBC result sets, a natural question that comes to mind is: What is the crucial difference between the two Is it just syntactic, using accessor methods instead of JDBC get calls to fetch column values No, the difference is not merely syntactic, although it may appear at first glance to be so. Unlike a JDBC ResultSet, an iterator represents the shape of the result rows. In our example, the NameAddrIter declaration specifies that the row has two columns, name and address, both of type String. This additional information supports early error detection through compile-time type-checking. If we pass an instance of this iterator as an argument to a method elsewhere in our code, the argument type must be of type NameAddrIter for the Java code to compile successfully. That is, static type-checking by the Java compiler prevents a wrong type of iterator from being passed to a method and causing run-time errors, say by accessing an invalid column position. The same compile-time checking does not apply for a JDBC ResultSet object, since it is a generic type representing any query result with no information about the query shape. Of course, SQLJ iterators are implemented using JDBC result sets, but they additionally provide the safer type-checking functionality through explicit declarations of the query shape. SQLJ iterators and JDBC result sets are designed to intemperate well with each other. Given a SQLJ iterator, the underlying JDBC result set can be retrieved by calling the getResultSet() method on the iterator. It is also possible to construct a SQLJ iterator instance from a JDBC result set (refer to the SQLJ documentation for details).
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