Berkeley DB Reference Guide: Using entities with collections
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### Berkeley DB Reference Guide: Java API Tutorial - Entity |

### Using entities with collections

In this example entity objects, rather than key and value objects, are used for adding and enumerating the records in a collection. Because fewer classes and objects are involved, adding and enumerating is done more conveniently and more simply than in the prior examples.

For adding and iterating entities, the collection of entities returned by Map.values is used. In general, when using an entity binding, all Java collection methods that are passed or returned a value object will be passed or returned an entity object instead.

The Sample class has been changed in this example to add objects using the Set.add method rather than the Map.put method that was used in the prior examples. Entity objects are constructed and passed to Set.add .

>     public class Sample
>     {
>         ...
>         private void addSuppliers()
>         {
>             Set suppliers = views.getSupplierSet();
>             if (suppliers.isEmpty())
>             {
>                 System.out.println("Adding Suppliers");
>                 suppliers.add(new Supplier("S1", "Smith", 20, "London"));
>                 suppliers.add(new Supplier("S2", "Jones", 10, "Paris"));
>                 suppliers.add(new Supplier("S3", "Blake", 30, "Paris"));
>                 suppliers.add(new Supplier("S4", "Clark", 20, "London"));
>                 suppliers.add(new Supplier("S5", "Adams", 30, "Athens"));
>             }
>         }

>         private void addParts()
>         {
>             Set parts = views.getPartSet();
>             if (parts.isEmpty())
>             {
>                 System.out.println("Adding Parts");
>                 parts.add(new Part("P1", "Nut", "Red",
>                           new Weight(12.0, Weight.GRAMS), "London"));
>                 parts.add(new Part("P2", "Bolt", "Green",
>                           new Weight(17.0, Weight.GRAMS), "Paris"));
>                 parts.add(new Part("P3", "Screw", "Blue",
>                           new Weight(17.0, Weight.GRAMS), "Rome"));
>                 parts.add(new Part("P4", "Screw", "Red",
>                           new Weight(14.0, Weight.GRAMS), "London"));
>                 parts.add(new Part("P5", "Cam", "Blue",
>                           new Weight(12.0, Weight.GRAMS), "Paris"));
>                 parts.add(new Part("P6", "Cog", "Red",
>                           new Weight(19.0, Weight.GRAMS), "London"));
>             }
>         }

>         private void addShipments()
>         {
>             Set shipments = views.getShipmentSet();
>             if (shipments.isEmpty())
>             {
>                 System.out.println("Adding Shipments");
>                 shipments.add(new Shipment("P1", "S1", 300));
>                 shipments.add(new Shipment("P2", "S1", 200));
>                 shipments.add(new Shipment("P3", "S1", 400));
>                 shipments.add(new Shipment("P4", "S1", 200));
>                 shipments.add(new Shipment("P5", "S1", 100));
>                 shipments.add(new Shipment("P6", "S1", 100));
>                 shipments.add(new Shipment("P1", "S2", 300));
>                 shipments.add(new Shipment("P2", "S2", 400));
>                 shipments.add(new Shipment("P2", "S3", 200));
>                 shipments.add(new Shipment("P2", "S4", 200));
>                 shipments.add(new Shipment("P4", "S4", 300));
>                 shipments.add(new Shipment("P5", "S4", 400));
>             }
>         }

Instead of printing the key/value pairs by iterating over the Map.entrySet as done in the prior example, this example iterates over the entities in the Map.values collection.

>     import com.sleepycat.bdb.collection.StoredIterator;
>     import java.util.Iterator;
>     import java.util.Set;
>     ...
>     public class Sample
>     {
>         ...
>         private class PrintDatabase implements TransactionWorker
>         {
>             public void doWork()
>                 throws Exception
>             {
>                 printValues("Parts",
>                              views.getPartSet().iterator());
>                 printValues("Suppliers",
>                              views.getSupplierSet().iterator());
>                 printValues("Suppliers for City Paris",
>                              views.getSupplierByCityMap().duplicates(
>                                                 "Paris").iterator());
>                 printValues("Shipments",
>                              views.getShipmentSet().iterator());
>                 printValues("Shipments for Part P1",
>                              views.getShipmentByPartMap().duplicates(
>                                                 new PartKey("P1")).iterator());
>                 printValues("Shipments for Supplier S1",
>                              views.getShipmentBySupplierMap().duplicates(
>                                                 new SupplierKey("S1")).iterator());
>             }
>         }
>     }

The output of the example program is shown below.

>     Adding Suppliers
>     Adding Parts
>     Adding Shipments

>     --- Parts ---
>     Part: number=P1 name=Nut color=Red weight=[12.0 grams] city=London
>     Part: number=P2 name=Bolt color=Green weight=[17.0 grams] city=Paris
>     Part: number=P3 name=Screw color=Blue weight=[17.0 grams] city=Rome
>     Part: number=P4 name=Screw color=Red weight=[14.0 grams] city=London
>     Part: number=P5 name=Cam color=Blue weight=[12.0 grams] city=Paris
>     Part: number=P6 name=Cog color=Red weight=[19.0 grams] city=London

>     --- Suppliers ---
>     Supplier: number=S1 name=Smith status=20 city=London
>     Supplier: number=S2 name=Jones status=10 city=Paris
>     Supplier: number=S3 name=Blake status=30 city=Paris
>     Supplier: number=S4 name=Clark status=20 city=London
>     Supplier: number=S5 name=Adams status=30 city=Athens

>     --- Suppliers for City Paris ---
>     Supplier: number=S2 name=Jones status=10 city=Paris
>     Supplier: number=S3 name=Blake status=30 city=Paris

>     --- Shipments ---
>     Shipment: part=P1 supplier=S1 quantity=300
>     Shipment: part=P1 supplier=S2 quantity=300
>     Shipment: part=P2 supplier=S1 quantity=200
>     Shipment: part=P2 supplier=S2 quantity=400
>     Shipment: part=P2 supplier=S3 quantity=200
>     Shipment: part=P2 supplier=S4 quantity=200
>     Shipment: part=P3 supplier=S1 quantity=400
>     Shipment: part=P4 supplier=S1 quantity=200
>     Shipment: part=P4 supplier=S4 quantity=300
>     Shipment: part=P5 supplier=S1 quantity=100
>     Shipment: part=P5 supplier=S4 quantity=400
>     Shipment: part=P6 supplier=S1 quantity=100

>     --- Shipments for Part P1 ---
>     Shipment: part=P1 supplier=S1 quantity=300
>     Shipment: part=P1 supplier=S2 quantity=300

>     --- Shipments for Supplier S1 ---
>     Shipment: part=P1 supplier=S1 quantity=300
>     Shipment: part=P2 supplier=S1 quantity=200
>     Shipment: part=P3 supplier=S1 quantity=400
>     Shipment: part=P4 supplier=S1 quantity=200
>     Shipment: part=P5 supplier=S1 quantity=100
>     Shipment: part=P6 supplier=S1 quantity=100

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