/// <summary>
/// Parses a group by expression.
/// Group by expression consists only of expressions separated by comma.
/// GroupBy -> GROUP BY GroupByTerm (, GroupByTerm)*
/// GroupByTerm -> Expression
/// </summary>
/// <returns> A tree representation of a group by or null if the tokens are missing group token on its first position. </returns>
static public GroupByNode ParseGroupBy(ref int position, List <Token> tokens)
{
GroupByNode groupByNode = new GroupByNode();
// We expect after reading match expr that the position is set on the Group token.
// GROUP
if (!CheckToken(position, Token.TokenType.Group, tokens))
{
return(null);
}
else
{
position++;
// BY
if (!CheckToken(position, Token.TokenType.By, tokens))
{
ThrowError("Group by parser", "Expected BY token.", position, tokens);
}
else
{
position++;
}
Node node = ParseGroupByTerm(ref position, tokens);
if (node == null)
{
ThrowError("Group by parser", "Failed to parse group by expresion. Expected group by term.", position, tokens);
}
groupByNode.AddNext(node);
return(groupByNode);
}
}
/// <summary>
/// A root node of the parse tree.
/// Jumps to thxe node under the root.
/// There must be always at least one result.
/// </summary>
public void Visit(GroupByNode node)
{
node.next.Accept(this);
if (this.holders.Count == 0)
{
throw new ArgumentException($"{this.GetType()}, the final results is empty or null.");
}
}
public void Visit(GroupByNode node)
{
throw new NotImplementedException();
}
/// <summary>
/// Parses Group by parse tree, the information is stored in the expression info class.
/// The reason this method is separated from constructor is because it cannot guess whether the
/// clause is a normal group by or a single group group by, thus the group by must always be parsed
/// as the first clause after the Match clause.
/// </summary>
public static void ParseGroupBy(Graph graph, VariableMap variableMap, IGroupByExecutionHelper executionHelper, GroupByNode groupByNode, QueryExpressionInfo exprInfo)
{
if (executionHelper == null || groupByNode == null || variableMap == null || graph == null || exprInfo == null)
{
throw new ArgumentNullException($"Group by results processor, passing null arguments to the constructor.");
}
var groupbyVisitor = new GroupByVisitor(graph.labels, variableMap, exprInfo);
groupbyVisitor.Visit(groupByNode);
executionHelper.IsSetGroupBy = true;
}
/// <summary>
/// Creates a group by object for multigroup group by (defined group by clause).
/// </summary>
/// <param name="graph"> A property graph. </param>
/// <param name="variableMap"> A variable map. </param>
/// <param name="executionHelper"> A group by execution helper. </param>
/// <param name="groupByNode"> A parsed tree of group by expression. </param>
/// <param name="exprInfo"> A query expression information. </param>
public GroupByObject(Graph graph, VariableMap variableMap, IGroupByExecutionHelper executionHelper, GroupByNode groupByNode, QueryExpressionInfo exprInfo)
{
if (executionHelper == null || groupByNode == null || variableMap == null || graph == null || exprInfo == null)
{
throw new ArgumentNullException($"{this.GetType()}, passing null arguments to the constructor.");
}
this.helper = executionHelper;
var groupbyVisitor = new GroupByVisitor(graph.labels, variableMap, exprInfo);
groupbyVisitor.Visit(groupByNode);
this.hashes = groupbyVisitor.GetResult().ToArray();
this.aggregates = exprInfo.Aggregates;
this.helper.IsSetGroupBy = true;
}
