/// <summary>
/// The root node of the parse tree.
/// Jumps to the next node under the root.
/// There must be at least one variable node.
/// </summary>
public void Visit(SelectNode node)
{
node.next.Accept(this);
if (result.Count < 1)
{
throw new ArgumentException($"{ this.GetType()}, final result is empty or null.");
}
}
/// <summary>
/// Parses a select query part.
/// Select is only parsing expressions separated by comma.
/// Select -> SELECT (*|(SelectPrintTerm (, SelectPrintTerm)*)
/// SelectPrintTerm -> Expression
/// </summary>
/// <returns> A tree representation of a SELECT query part. </returns>
static public SelectNode ParseSelect(ref int position, List <Token> tokens)
{
SelectNode selectNode = new SelectNode();
// Parsing Select always starts at position 0.
if (position > 0 || tokens[position].type != Token.TokenType.Select)
{
ThrowError("Select parser", "Failed to find SELECT token.", position, tokens);
}
else
{
position++;
Node node = ParseVarExprForSelect(ref position, tokens);
if (node == null)
{
ThrowError("Select parser", "Expected Select print term.", position, tokens);
}
selectNode.AddNext(node);
}
return(selectNode);
}
public void Visit(SelectNode node)
{
throw new NotImplementedException();
}
/// <summary>
/// Creates a Select object.
/// Parsing is done beforehand because first we need to parse match expression for variable definitions.
/// </summary>
/// <param name="graph"> A property graph. </param>
/// <param name="map"> A variable map. </param>
/// <param name="executionHelper"> A select execution helper. </param>
/// <param name="selectNode"> A parsed tree of select expression. </param>
/// <param name="exprInfo"> A query expression information. </param>
public SelectObject(Graph graph, VariableMap map, ISelectExecutionHelper executionHelper, SelectNode selectNode, QueryExpressionInfo exprInfo)
{
if (executionHelper == null || selectNode == null || exprInfo == null)
{
throw new ArgumentNullException($"{this.GetType()}, passing null arguments to constructor. ");
}
this.helper = executionHelper;
// Process the parse tree and creates a List of expression to be printed.
SelectVisitor visitor = new SelectVisitor(graph.labels, map, exprInfo);
selectNode.Accept(visitor);
this.rowFormat = visitor.GetResult();
}
