/** rewrites the subop of assign. */
@Override
public void visit(final OpAssign opAssign) {
if (LOG.isDebugEnabled()) {
LOG.debug("Starting visiting OpAssign");
}
addOp(OpAssign.assign(rewriteOp1(opAssign), opAssign.getVarExprList()));
}
@Override
public Op transform(OpGraph opGraph, Op op) {
// ?? Could just leave the (graph) in place always - just rewrite BGPs.
boolean noPattern = false;
/* One case to consider is when the pattern for the GRAPH
* statement includes uses the variable inside the GRAPH clause.
* In this case, we must rename away the inner variable
* to allow stream execution via index joins,
* and then put back the value via an assign.
* (This is what QueryIterGraph does using a streaming join
* for triples)
*/
// Note: op is already quads by this point.
// Must test scoping by the subOp of GRAPH
QuadSlot qSlot = tracker.peek();
Node actualName = qSlot.actualGraphName;
Node rewriteName = qSlot.rewriteGraphName;
if (OpBGP.isBGP(op)) {
// Empty BGP
if (((OpBGP) op).getPattern().isEmpty()) noPattern = true;
} else if (op instanceof OpTable) {
// Empty BGP compiled to a unit table
if (((OpTable) op).isJoinIdentity()) noPattern = true;
}
if (noPattern) {
// The case of something like:
// GRAPH ?g {} or GRAPH <v> {}
// which are ways of accessing the names in the dataset.
return new OpDatasetNames(opGraph.getNode());
}
if (actualName != rewriteName)
op = OpAssign.assign(op, Var.alloc(actualName), new ExprVar(rewriteName));
// Drop (graph...) because inside nodes
// have been converted to quads.
return op;
}
public void visit(OpAssign opAssign) {
Table table = eval(opAssign.getSubOp());
table = evaluator.assign(table, opAssign.getVarExprList());
push(table);
}