private static Map<Symbol, Symbol> computeIdentityTranslations(
Map<Symbol, Expression> assignments) {
Map<Symbol, Symbol> inputToOutput = new HashMap<>();
for (Map.Entry<Symbol, Expression> assignment : assignments.entrySet()) {
if (assignment.getValue() instanceof SymbolReference) {
inputToOutput.put(Symbol.from(assignment.getValue()), assignment.getKey());
}
}
return inputToOutput;
}
@Override
public ActualProperties visitProject(ProjectNode node, List<ActualProperties> inputProperties) {
ActualProperties properties = Iterables.getOnlyElement(inputProperties);
Map<Symbol, Symbol> identities = computeIdentityTranslations(node.getAssignments());
ActualProperties translatedProperties =
properties.translate(column -> Optional.ofNullable(identities.get(column)));
// Extract additional constants
Map<Symbol, NullableValue> constants = new HashMap<>();
for (Map.Entry<Symbol, Expression> assignment : node.getAssignments().entrySet()) {
Expression expression = assignment.getValue();
IdentityHashMap<Expression, Type> expressionTypes =
getExpressionTypes(
session,
metadata,
parser,
types,
expression,
emptyList() /* parameters already replaced */);
Type type = requireNonNull(expressionTypes.get(expression));
ExpressionInterpreter optimizer =
ExpressionInterpreter.expressionOptimizer(
expression, metadata, session, expressionTypes);
// TODO:
// We want to use a symbol resolver that looks up in the constants from the input subplan
// to take advantage of constant-folding for complex expressions
// However, that currently causes errors when those expressions operate on arrays or row
// types
// ("ROW comparison not supported for fields with null elements", etc)
Object value = optimizer.optimize(NoOpSymbolResolver.INSTANCE);
if (value instanceof SymbolReference) {
Symbol symbol = Symbol.from((SymbolReference) value);
NullableValue existingConstantValue = constants.get(symbol);
if (existingConstantValue != null) {
constants.put(assignment.getKey(), new NullableValue(type, value));
}
} else if (!(value instanceof Expression)) {
constants.put(assignment.getKey(), new NullableValue(type, value));
}
}
constants.putAll(translatedProperties.getConstants());
return ActualProperties.builderFrom(translatedProperties).constants(constants).build();
}