18.8 Java APIs for Executing UPDATE Queries

The UPDATE queries make changes to existing graphs using the INSERT, UPDATE, and DELETE operations.

Note that INSERT allows you to insert new vertices and edges into a graph, UPDATE allows you to update existing vertices and edges by setting their properties to new values, and DELETE allows you to delete vertices and edges from a graph.

• Updatability of Graphs Through PGQL
  Graph data that is loaded from the Oracle RDBMS or from CSV files into the PGX is not updatable through PGQL right away.
• Executing UPDATE Queries Against a Graph in the Graph Server (PGX)
  To execute UPDATE queries against a graph, use the PgxGraph.executePgql(String query) method.
• Executing UPDATE Queries Against a PGX Session
  You can also execute UPDATE queries against a PgxSession.
• Altering the Underlying Schema of a Graph
  The INSERT operations can only insert vertices and edges with known labels and properties. Similarly, UPDATE operations can only set values of known properties. Thus, new data must always conform to the existing schema of the graph.

18.8.1 Updatability of Graphs Through PGQL

Graph data that is loaded from the Oracle RDBMS or from CSV files into the PGX is not updatable through PGQL right away.

First, you need to create a copy of the data through the PgxGraph.clone() method. The resulting graph is fully updatable.

Consider the following example:

// load a graph from the RDBMS or from CSV
PgxGraph g1 = session.readGraphByName("<graph>",GraphSource.PG_PGQL);

// create an updatable copy of the graph
PgxGraph g2 = g1.clone("new_graph_name");

// insert an additional vertex into the graph
g2.executePgql("INSERT VERTEX v " +
               "         LABELS ( Person ) " +
               "         PROPERTIES ( v.firstName = 'Camille', " +
               "                      v.lastName = ' Mullins')"); 

Additionally, there is also a PgxGraph.cloneAndExecutePgql(String query, String graphName) method that combines the last two steps from above example into a single step:

// create an updatable copy of the graph while inserting a new vertex
PgxGraph g2_copy = g1.cloneAndExecutePgql(
                     "INSERT VERTEX v " +
                     "         LABELS ( Person ) " +
                     "         PROPERTIES ( v.firstName = 'Camille', " +
                     "                      v.lastName = ' Mullins') "
                   , "new_graph_name");

Note that graphs that are created through PgxGraph.clone() are local to the session. However, they can be shared with other sessions through the PgxGraph.publish(..) methods but then they are no longer updatable through PGQL. Only session-local graphs are updatable but persistent graphs are not.

18.8.2 Executing UPDATE Queries Against a Graph in the Graph Server (PGX)

To execute UPDATE queries against a graph, use the PgxGraph.executePgql(String query) method.

The following is an example of INSERT query:

g.executePgql("INSERT VERTEX v " +
              "         LABELS ( Person ) " +
              "         PROPERTIES ( v.firstName = 'Camille', " +
              "                      v.lastName = ' Mullins' ) "); 

Note that the INTO clause of the INSERT can be omitted. If you use an INTO clause, the graph name in the INTO clause must correspond to the name of the PGX graph (PgxGraph.getName()) that the query is executed against.

The following is an example of UPDATE query:

// set the date of birth of Camille to 2014-11-15
g.executePgql("UPDATE v SET ( v.dob = DATE '2014-11-14' ) " +
              "FROM MATCH (v:Person) " +
              "WHERE v.firstName = 'Camille' AND v.lastName = ' Mullins' "); 

The following is an example of DELETE query:

// delete Camille from the graph
g.executePgql("DELETE v " +
              "FROM MATCH (v:Person) " +
              "WHERE v.firstName = 'Camille' AND v.lastName = 'Mullins' "); 

18.8.3 Executing UPDATE Queries Against a PGX Session

You can also execute UPDATE queries against a PgxSession.

The following example clones a graph and runs UPDATE queries against the PgxSession.

//Loads the graph into the graph server (PGX)
PgxGraph g1 = session.readGraphByName("BANK_GRAPH_VIEW",GraphSource.PG_PGQL);
//Clones the graph
PgxGraph g2 = g1.clone("BANK_GRAPH_NEW");
//Get the graph
session.getGraph("BANK_GRAPH_NEW");
//Insert vertices and an edge connecting the vertices into the graph
session.executePgql(
     "INSERT INTO BANK_GRAPH_NEW "+
     "   VERTEX v1 LABELS (Accounts) PROPERTIES (v1.id=1001, v1.name='New account-1') "+
     ",  VERTEX v2 LABELS (Accounts) PROPERTIES (v2.id=1002, v2.name='New account-2') "+
     ",  EDGE e1 BETWEEN v1 AND v2 LABELS (Transfers) PROPERTIES (e1.amount=3000) "
);
//Query the graph to verify the newly added edge
session.executePgql(
     "SELECT e.amount FROM MATCH (v1:Accounts) -[e:Transfers]-> (v2:Accounts) "+
     "ON BANK_GRAPH_NEW "+
     "WHERE v1.id=1001 AND v2.id=1002"
);

18.8.4 Altering the Underlying Schema of a Graph

The INSERT operations can only insert vertices and edges with known labels and properties. Similarly, UPDATE operations can only set values of known properties. Thus, new data must always conform to the existing schema of the graph.

However, some PGX APIs exist for updating the schema of a graph: while no APIs exist for adding new labels, new properties can be added through the PgxGraph.createVertexProperty(PropertyType type, String name) and PgxGraph.createEdgeProperty(PropertyType type, String name) methods. The new properties are attached to each vertex/edge in the graph, irrespective of their labels. Initially the properties are assigned a default value but then the values can be updated through the UPDATE statements.

Consider the following example:

// load a graph from the RDBMS or from CSV
PgxGraph g = session.readGraphByName("<graph>",GraphSource.PG_PGQL);

// add a new property to the graph
g.createVertexProperty(PropertyType.LOCAL_DATE, "dob");

// set the date of birth of Camille to 2014-11-15
g.executePgql("UPDATE v SET ( v.dob = DATE '2014-11-14' ) " +
              "FROM MATCH (v:Person) " +
              "WHERE v.firstName = 'Camille' AND v.lastName = ' Mullins' ");