6.9.1.4.6.4 Options for Partial Object Construction

When reading edges from a query result, there are two possible behaviors when adding the start and end vertex to any local caches:

• Add only the vertex ID, which is available from the edge itself. This option is the default, for efficiency.

• Add the vertex ID, and retrieve all properties for the start and end vertex. For this behavior, you can call setPartial(true) on each OracleVertex object constructed from your PGQL query result set.

Example 6-21 PgqlExample14.java

PgqlExample14.java illustrates this difference in behavior. This program first executes a query to retrieve all edges, which causes the incident vertices to be added to a local cache. The second query retrieves all vertices. The program then prints each OracleVertex object to show which properties have been loaded.

import java.sql.Connection;

import oracle.pg.rdbms.Oracle;
import oracle.pg.rdbms.OraclePropertyGraph;
import oracle.pg.rdbms.OracleVertex;

import oracle.pg.rdbms.pgql.PgqlConnection;
import oracle.pg.rdbms.pgql.PgqlResultSet;
import oracle.pg.rdbms.pgql.PgqlStatement;

import oracle.ucp.jdbc.PoolDataSourceFactory;
import oracle.ucp.jdbc.PoolDataSource;

/**
 * This example shows the behavior of setPartial(true) for OracleVertex objects
 * created from PGQL query results.
 */
public class PgqlExample14
{

  public static void main(String[] args) throws Exception
  {
    int idx=0;
    String host               = args[idx++]; 
    String port               = args[idx++]; 
    String sid                = args[idx++]; 
    String user               = args[idx++]; 
    String password           = args[idx++];
    String graph              = args[idx++];

    Connection conn = null;
    Oracle oracle = null;
    OraclePropertyGraph opg = null;
    PgqlStatement ps = null;
    PgqlResultSet rs = null;

    try {

      //Get a jdbc connection
      PoolDataSource  pds = PoolDataSourceFactory.getPoolDataSource();
      pds.setConnectionFactoryClassName("oracle.jdbc.pool.OracleDataSource");
      pds.setURL("jdbc:oracle:thin:@"+host+":"+port +":"+sid);
      pds.setUser(user);
      pds.setPassword(password);     
      conn = pds.getConnection();

      // Get a PGQL connection
      PgqlConnection pgqlConn = PgqlConnection.getConnection(conn);
      pgqlConn.setGraph(graph);

      // Create a PgqlStatement
      ps = pgqlConn.createStatement();

      // Query to illustrate set partial
      String pgql =
        "SELECT id(e), label(e) "+
        "FROM MATCH (v1)-[e:\"knows\"]->(v2)";

      // execute query
      rs = ps.executeQuery(pgql, " ");

      // print results
      System.out.println("-- Results for edge query -----------------");
      rs.print();

      // close result set
      rs.close();

      // Create an Oracle Property Graph instance
      oracle = new Oracle(conn);
      opg = OraclePropertyGraph.getInstance(oracle,graph);

      // Query to retrieve vertices
      pgql =
        "SELECT id(v) "+
        "FROM MATCH (v)";

      // Get each vertex object in result and print with toString()
      rs = ps.executeQuery(pgql, " ");

      // iterate through result
      System.out.println("-- Vertex objects retrieved from vertex query --");
      while (rs.next()) {
        Long vid = rs.getLong(1);
        OracleVertex v = OracleVertex.getInstance(opg, vid);
        System.out.println(v.toString());
      }
      // close result set
      rs.close();

      // Execute the same query but call setPartial(true) for each vertex
      rs = ps.executeQuery(pgql, " ");
      System.out.println("-- Vertex objects retrieved from vertex query with setPartial(true) --");
      while (rs.next()) {
        Long vid = rs.getLong(1);
        OracleVertex v = OracleVertex.getInstance(opg, vid);
        v.setPartial(true);
        System.out.println(v.toString());
      }
      // close result set
      rs.close();
    }
    finally {
      // close the result set
      if (rs != null) {
        rs.close();
      }
      // close the statement
      if (ps != null) {
        ps.close();
      }
      // close the connection
      if (conn != null) {
        conn.close();
      }
      // close the property graph
      if (opg != null) {
        opg.close();
      }
      // close oracle
      if (oracle != null) {
        oracle.dispose();
      }
    }
  }
}

The output for PgqlExample14.java (which can be loaded using GraphLoaderExample.java code) is:

-- Results for edge query -----------------
+------------------+
| id(e) | label(e) |
+------------------+
| 6     | knows    |
| 11    | knows    |
| 10    | knows    |
| 5     | knows    |
| 4     | knows    |
| 13    | knows    |
| 9     | knows    |
| 12    | knows    |
| 8     | knows    |
| 7     | knows    |
| 14    | knows    |
| 15    | knows    |
+------------------+
-- Vertex objects retrieved from vertex query --
Vertex ID 3 [NULL] {}
Vertex ID 0 [NULL] {}
Vertex ID 2 [NULL] {}
Vertex ID 1 [NULL] {}
-- Vertex objects retrieved from vertex query with setPartial(true) --
Vertex ID 3 [NULL] {bval:bol:false, fname:str:Susan, lname:str:Blue, mval:bol:false, age:int:35}
Vertex ID 0 [NULL] {bval:bol:true, fname:str:Bill, lname:str:Brown, mval:str:y, age:int:40}
Vertex ID 2 [NULL] {fname:str:Ray, lname:str:Green, mval:dat:1985-01-01 04:00:00.0, age:int:41}
Vertex ID 1 [NULL] {bval:bol:true, fname:str:John, lname:str:Black, mval:int:27, age:int:30}