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CHAPTER 9 USING WEAKLY TYPED STRUCT OBJECTS
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As the first step, we retrieve the attributes of the object we selected earlier by invoking the method _getItem(): Object[] itemAttributes = itemStruct.getAttributes(); We modify the third attribute (the description) to a new value. This change happens only in memory. itemAttributes[2] = "item2 desc updated using prepared statement"; Next, we need to create the modified Struct object for which the first step is to retrieve the StructDescriptor from the object already selected: StructDescriptor itemDescriptor = itemSTRUCT.getDescriptor(); Then we create the STRUCT object with the modified attributes: Struct itemObject = new STRUCT ( itemDescriptor, conn, itemAttributes ); and use the standard update statement (note the use of the value() function again) to carry out the update: pstmt = conn.prepareStatement( "update item_table it set value(it) = " + " where it.id = " ); pstmt.setObject(1, itemObject ); pstmt.setInt(2, itemID ); int numOfRowsUpdated = pstmt.executeUpdate(); System.out.println( "Updated " + numOfRowsUpdated + " rows"); conn.commit(); } finally { // release resources in the finally clause. JDBCUtil.close( pstmt); } }
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Performing Updates Using Relational SQL
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The method _demoUpdateUsingRelationalSQL() uses a relational SQL to carry out the same update in one step: private static void _demoUpdateUsingRelationalSQL( Connection conn, int itemID) throws SQLException { PreparedStatement pstmt = null; try {
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CHAPTER 9 USING WEAKLY TYPED STRUCT OBJECTS
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The main difference in this case is the relational SQL, which directly changes the description attribute in the table as presented here. The rest of the code is straightforward. pstmt = conn.prepareStatement( "update item_table it set it.description= " + " where it.id = " ); pstmt.setString(1, "item desc updated using relational SQL" ); pstmt.setInt(2, itemID ); int numOfRowsUpdated = pstmt.executeUpdate(); System.out.println( "Updated " + numOfRowsUpdated + " rows"); conn.commit(); } finally { // release resources in the finally clause. JDBCUtil.close( pstmt); } } } If we run the program, we get the following output: B:\>java StructUpdateExample URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(PORT=1521) (HOST=rmenon-lap))(CONNECT_DATA=(SID=ora10g))) printing query results ... Updated 1 rows Updated 1 rows Using the following query, we verify that our updates have been successful: benchmark@ORA10G> select * from item_table it order by it.id; ID --1 2 NAME ---------item1 item2 DESCRIPTION ----------------------------------item1 desc item2 desc updated using prepared s tatement item desc updated using relational SQL
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As this section demonstrated, performing an update using an oracle.sql.STRUCT object is complicated. The fact that the update is carried out in two operations (a select for update followed by an update operation) means that it is also slower as compared to its relational SQL counterpart.
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CHAPTER 9 USING WEAKLY TYPED STRUCT OBJECTS
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The process of deleting objects typically is the same as in a normal relational delete case, for example: "delete from item_table it where it.id = " I encourage you to write code for deleting a value from the table item_table yourself.
Summary
This chapter defined weakly typed and strongly typed objects. You learned how to use the Struct interface to select objects as a collection of attributes. You also learned how to insert and update objects stored in tables using oracle.sql.STRUCT class methods. The steps involved in these operations tend to be more complicated than the straightforward relational alternative. You saw that this is particularly true when performing updates. In the next chapter, you will learn how to access and manipulate objects in tables using strongly typed objects.
CHAPTER
Using Strongly Typed Interfaces with JPublisher
n the previous chapter, we examined the technique of using the Struct interface to materialize database objects as a generic collection of attributes. This technique works well for a small set of applications that needs to treat different object types in a generic manner. However, this technique does not satisfy the requirements of the majority of object-oriented applications that require you to work in terms of actual objects instead of a loose collection of attributes. In this chapter, we discuss the alternative of using strongly typed interfaces to create custom Java classes that correspond to Oracle objects in the database. Using this technique, you can generate a custom class for each object type in the database, making it possible to manipulate the contents in memory in a more natural fashion (i.e., using proper getter and setter methods for the attributes instead of indexing into a generic Object[]). You will first consider what strongly typed interfaces are. Then, you will learn how to use JPublisher, a utility that allows you to generate custom classes corresponding to Oracle object types. You will use JPublisher to generate custom classes that implement either the standard interface SQLData or the Oracle extension interfaces ORAData and ORADataFactory. Let s begin with an introduction to strongly typed interfaces.
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