In previous chapters in this book, we built applications that load and display several DB databases. In this example, we will extend those examples to use secondary databases. Specifically:
In Stored Class Catalog Management with MyDbs we built a
class that we can use to open several Database objects.
In Opening Secondary Databases with MyDbs we will extend
that class to also open and manage a SecondaryDatabase.
In Cursor Example we
built an application to display our inventory database (and related
vendor information). In Using Secondary Databases with ExampleDatabaseRead we will extend that application to
show inventory records based on the index we cause to be loaded using
ExampleDatabaseLoad.
Before we can use a secondary database, we must implement a class to extract secondary keys for us.
We use ItemNameKeyCreator for this purpose.
Example 10.1 ItemNameKeyCreator.java
This class assumes the primary database
uses Inventory objects for the record data. The
Inventory class is described in Inventory.java.
In our key creator class, we make use of a custom tuple binding
called InventoryBinding. This class is described in InventoryBinding.java.
You can find InventoryBinding.java in:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.
package db.GettingStarted;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.SecondaryDatabase;
import com.sleepycat.db.SecondaryKeyCreator;
import com.sleepycat.bind.tuple.TupleBinding;
import java.io.IOException;
public class ItemNameKeyCreator implements SecondaryKeyCreator {
private TupleBinding theBinding;
// Use the constructor to set the tuple binding
ItemNameKeyCreator(TupleBinding binding) {
theBinding = binding;
}
// Abstract method that we must implement
public boolean createSecondaryKey(SecondaryDatabase secDb,
DatabaseEntry keyEntry, // From the primary
DatabaseEntry dataEntry, // From the primary
DatabaseEntry resultEntry) // set the key data on this.
throws DatabaseException {
try {
// Convert dataEntry to an Inventory object
Inventory inventoryItem =
(Inventory) theBinding.entryToObject(dataEntry);
// Get the item name and use that as the key
String theItem = inventoryItem.getItemName();
resultEntry.setData(theItem.getBytes("UTF-8"));
} catch (IOException willNeverOccur) {}
return true;
}
}
Now that we have a key creator, we can use it to generate keys for a
secondary database. We will now extend MyDbs
to manage a secondary database, and to use
ItemNameKeyCreator to generate keys for that
secondary database.
In Stored Class Catalog Management with MyDbs we built
MyDbs as an example of a class that
encapsulates
Database opens and closes. We will now extend
that class to manage a SecondaryDatabase.
Example 10.2 SecondaryDatabase Management with MyDbs
We start by importing two additional classes needed to support secondary databases. We also add a global variable to use as a handle for our secondary database.
// File MyDbs.java
package db.GettingStarted;
import java.io.FileNotFoundException;
import com.sleepycat.bind.serial.StoredClassCatalog;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.DatabaseType;
import com.sleepycat.db.SecondaryConfig;
import com.sleepycat.db.SecondaryDatabase;
public class MyDbs {
// The databases that our application uses
private Database vendorDb = null;
private Database inventoryDb = null;
private Database classCatalogDb = null;
private SecondaryDatabase itemNameIndexDb = null;
private String vendordb = "VendorDB.db";
private String inventorydb = "InventoryDB.db";
private String classcatalogdb = "ClassCatalogDB.db";
private String itemnameindexdb = "ItemNameIndexDB.db";
// Needed for object serialization
private StoredClassCatalog classCatalog;
// Our constructor does nothing
public MyDbs() {}
Next we update the MyDbs.setup() method to open the
secondary database. As a part of this, we have to pass an
ItemNameKeyCreator object on the call to open the secondary
database. Also, in order to instantiate ItemNameKeyCreator, we need an
InventoryBinding object (we described this class in
InventoryBinding.java).
We do all this work together inside of MyDbs.setup().
public void setup(String databasesHome)
throws DatabaseException {
DatabaseConfig myDbConfig = new DatabaseConfig();
SecondaryConfig mySecConfig = new SecondaryConfig();
myDbConfig.setErrorStream(System.err);
mySecConfig.setErrorStream(System.err);
myDbConfig.setErrorPrefix("MyDbs");
mySecConfig.setErrorPrefix("MyDbs");
myDbConfig.setType(DatabaseType.BTREE);
mySecConfig.setType(DatabaseType.BTREE);
myDbConfig.setAllowCreate(true);
mySecConfig.setAllowCreate(true);
// Now open, or create and open, our databases
// Open the vendors and inventory databases
try {
vendordb = databasesHome + "/" + vendordb;
vendorDb = new Database(vendordb,
null,
myDbConfig);
inventorydb = databasesHome + "/" + inventorydb;
inventoryDb = new Database(inventorydb,
null,
myDbConfig);
// Open the class catalog db. This is used to
// optimize class serialization.
classcatalogdb = databasesHome + "/" + classcatalogdb;
classCatalogDb = new Database(classcatalogdb,
null,
myDbConfig);
} catch(FileNotFoundException fnfe) {
System.err.println("MyDbs: " + fnfe.toString());
System.exit(-1);
}
// Create our class catalog
classCatalog = new StoredClassCatalog(classCatalogDb);
// Need a tuple binding for the Inventory class.
// We use the InventoryBinding class
// that we implemented for this purpose.
TupleBinding inventoryBinding = new InventoryBinding();
// Open the secondary database. We use this to create a
// secondary index for the inventory database
// We want to maintain an index for the inventory entries based
// on the item name. So, instantiate the appropriate key creator
// and open a secondary database.
ItemNameKeyCreator keyCreator =
new ItemNameKeyCreator(new InventoryBinding());
// Set up additional secondary properties
// Need to allow duplicates for our secondary database
mySecConfig.setSortedDuplicates(true);
mySecConfig.setAllowPopulate(true); // Allow autopopulate
mySecConfig.setKeyCreator(keyCreator);
// Now open it
try {
itemnameindexdb = databasesHome + "/" + itemnameindexdb;
itemNameIndexDb = new SecondaryDatabase(itemnameindexdb,
null,
inventoryDb,
mySecConfig);
} catch(FileNotFoundException fnfe) {
System.err.println("MyDbs: " + fnfe.toString());
System.exit(-1);
}
}
Next we need an additional getter method for returning the secondary database.
public SecondaryDatabase getNameIndexDB() {
return itemNameIndexDb;
}
Finally, we need to update the MyDbs.close()
method to close the new secondary database. We want to make sure that
the secondary is closed before the primaries. While
this is not necessary for this example because our
closes are single-threaded, it is still a good habit to adopt.
public void close() {
try {
if (itemNameIndexDb != null) {
itemNameIndexDb.close();
}
if (vendorDb != null) {
vendorDb.close();
}
if (inventoryDb != null) {
inventoryDb.close();
}
if (classCatalogDb != null) {
classCatalogDb.close();
}
} catch(DatabaseException dbe) {
System.err.println("Error closing MyDbs: " +
dbe.toString());
System.exit(-1);
}
}
}
That completes our update to MyDbs. You
can find the complete class implementation in:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.
Because we performed all our secondary database configuration management in
MyDbs, we do not need to modify ExampleDatabaseLoad at all in
order to create our secondary indices. When ExampleDatabaseLoad calls
MyDbs.setup(), all of the necessary work is performed for us.
However, we still need to take advantage of the new secondary indices. We do this by updating
ExampleDatabaseRead to allow us to query for an inventory record based on its name.
Remember that the primary key for an inventory record is the item's SKU. The item's name is contained in the
Inventory object that is stored as each record's data in the inventory database. But
our new secondary index now allows us to easily query based on the item's name.
For this update, we modify
ExampleDatabaseRead to accept a new command line switch,
-s, whose argument is the name of an inventory item.
If the switch is present on the command line call to
ExampleDatabaseRead, then the application will
use the secondary database to look up and display all the inventory
records with that item name. Note that we use a SecondaryCursor
to seek to the item name key and then display all matching records.
Remember that you can find ExampleDatabaseRead.java in:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.
Example 10.3 SecondaryDatabase usage with ExampleDatabaseRead
First we need to import an additional class in order to use the secondary cursor:
package db.GettingStarted;
import java.io.IOException;
import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.serial.SerialBinding;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.db.Cursor;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import com.sleepycat.db.SecondaryCursor;
Next we add a single global variable:
public class ExampleDatabaseRead {
private static String myDbsPath = "./";
// Encapsulates the database environment and databases.
private static MyDbs myDbs = new MyDbs();
private static TupleBinding inventoryBinding;
private static EntryBinding vendorBinding;
// The item to locate if the -s switch is used
private static String locateItem;
Next we update ExampleDatabaseRead.run() to
check to see if the locateItem global variable has a
value. If it does, then we show just those records related to the item
name passed on the -s switch.
private void run(String args[])
throws DatabaseException {
// Parse the arguments list
parseArgs(args);
myDbs.setup(myDbsPath);
// Setup our bindings.
inventoryBinding = new InventoryBinding();
vendorBinding =
new SerialBinding(myDbs.getClassCatalog(),
Vendor.class);
if (locateItem != null) {
showItem();
} else {
showAllInventory();
}
}
Finally, we need to implement ExampleDatabaseRead.showItem().
This is a fairly simple method that opens a secondary cursor,
and then displays every primary record that is related to the secondary
key identified by the locateItem global variable.
private void showItem() throws DatabaseException {
SecondaryCursor secCursor = null;
try {
// searchKey is the key that we want to find in the
// secondary db.
DatabaseEntry searchKey =
new DatabaseEntry(locateItem.getBytes("UTF-8"));
// foundKey and foundData are populated from the primary
// entry that is associated with the secondary db key.
DatabaseEntry foundKey = new DatabaseEntry();
DatabaseEntry foundData = new DatabaseEntry();
// open a secondary cursor
secCursor =
myDbs.getNameIndexDB().openSecondaryCursor(null, null);
// Search for the secondary database entry.
OperationStatus retVal =
secCursor.getSearchKey(searchKey, foundKey,
foundData, LockMode.DEFAULT);
// Display the entry, if one is found. Repeat until no more
// secondary duplicate entries are found
while(retVal == OperationStatus.SUCCESS) {
Inventory theInventory =
(Inventory)inventoryBinding.entryToObject(foundData);
displayInventoryRecord(foundKey, theInventory);
retVal = secCursor.getNextDup(searchKey, foundKey,
foundData, LockMode.DEFAULT);
}
} catch (Exception e) {
System.err.println("Error on inventory secondary cursor:");
System.err.println(e.toString());
e.printStackTrace();
} finally {
if (secCursor != null) {
secCursor.close();
}
}
}
The only other thing left to do is to update
ExampleDatabaseRead.parseArgs() to support the -s command
line switch. To see how this is done, see
ExampleDatabaseRead.java in:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.