Writing a new row to a table in the store, and updating an existing row are usually identical operations (although methods exist that work only if the row is being updated, or only if it is being created — these are described a little later in this section).
Remember that you can only write data to a table after it has been added to the store. See Introducing Oracle NoSQL Database Tables and Indexes for details.
To write a row to a table in the store:
Construct a handle for the table to which you want to
write. You do this by retrieving a
TableAPI interface instance using
KVStore.getTableAPI(). You then
use that instance to retrieve a handle for the desired table
using the TableAPI.getTable(). This
returns a Table interface instance.
TableAPI.getTable() is an
expensive call that requires server side access. From a
performance point of view, it is a mistake to call this
method whenever you need a table handle. Instead, call
this method for all relevant tables in the set up section
of your code, and then reuse those handles throughout
your application.
Use the Table instance
retrieved in the previous step to create a
Row interface instance.
You use the Table.createRow()
method to do this.
Write to each field in the Row
using Row.put().
Write the new row to the store using
TableAPI.put().
The following is a trivial example of writing a row to the
store. It assumes that the KVStore handle
has already been created.
package kvstore.basicExample;
import oracle.kv.KVStore;
import oracle.kv.table.Row;
import oracle.kv.table.Table;
import oracle.kv.table.TableAPI;
...
// KVStore handle creation is omitted for brevity
...
TableAPI tableH = kvstore.getTableAPI();
// The name you give to getTable() must be identical
// to the name that you gave the table when you created
// the table using the CREATE TABLE DDL statement.
Table myTable = tableH.getTable("myTable");
// Get a Row instance
Row row = myTable.createRow();
// Now put all of the cells in the row.
// This does NOT actually write the data to
// the store.
row.put("item", "Bolts");
row.put("description", "Hex head, stainless");
row.put("count", 5);
row.put("percentage", 0.2173913);
// Now write the table to the store.
// "item" is the row's primary key. If we had not set that value,
// this operation will throw an IllegalArgumentException.
tableH.put(row, null, null);
To write to a child table, first create the row in the parent table to which the child belongs. You do this by populating the parent row with data. Then you write the child table's row(s). When you do, you must specify the primary key used by the parent table, as well as the primary key used by the child table's rows.
For example, in Defining Child Tables we showed how to create a child table. To write data to that table, do this:
package kvstore.basicExample;
import oracle.kv.KVStore;
import oracle.kv.table.Row;
import oracle.kv.table.Table;
import oracle.kv.table.TableAPI;
...
// KVStore handle creation is omitted for brevity
...
TableAPI tableH = kvstore.getTableAPI();
// First, populate a row in the parent table
Table myTable = tableH.getTable("myTable");
// Get a Row instance
Row row = myTable.createRow();
// Now put all of the cells in the row.
row.put("itemCategory", "Bolts");
row.put("description", "Metric & US sizes");
// Now write the table row to the store.
tableH.put(row, null, null);
// Now populate the corresponding child table
Table myChildTable = tableH.getTable("myTable.myChildTable");
// Get a row instance
Row childRow = myChildTable.createRow();
// Populate the rows. Because the parent table's "itemCategory"
// field is a primary key, this must be populated in addition
// to all of the child table's rows
childRow.put("itemCategory", "Bolts");
childRow.put("itemSKU", "1392610");
childRow.put("itemDescription", "1/4-20 x 1/2 Grade 8 Hex");
childRow.put("price", new Float(11.99));
childRow.put("inventoryCount", 1457);
Beyond the very simple usage of the TableAPI.put()
method illustrated above, there are three other
put operations that you can use:
TableAPI.putIfAbsent()
This method will only put the row if the row's primary key value DOES NOT currently exist in the table. That is, this method is successful only if it results in a create operation.
TableAPI.putIfPresent()
This method will only put the row if the row's primary key value already exists in the table. That is, this method is only successful if it results in an update operation.
TableAPI.putIfVersion()
This method will put the row only if the value matches the supplied version information. For more information, see Using Row Versions.