/// <summary>
/// Visits an aggregation node.
/// Creates a new aggregation function based on the provided name.
/// And initilises parsing of the aggregation argument.
/// </summary>
public void Visit(AggregateFuncNode node)
{
Aggregate aggregate = null;
Type aggType = null;
if (node.next == null)
{
throw new ArgumentException($"{this.GetType()}, exprected aggregation arguments.");
}
else
{
// count(*)
if (node.next.GetType() == typeof(IdentifierNode))
{
if (node.funcName.ToLower() == "count" && ((IdentifierNode)node.next).value == "*")
{
aggregate = Aggregate.Factory("count", typeof(int), null);
aggType = typeof(int);
}
else
{
throw new ArgumentException($"{this.GetType()}, expected count(*).");
}
}
else
{
// Every other aggregation.
// The only possibility is that the next node is VariableNode.
// So the argument will be created in this.Expr, from this expr the holder must be created.
// After the holder is created the aggregation is created with the expression.
// After this process, the expression that will be returned is created -> aggregation reference.
node.next.Accept(this);
var tmpHolder = new ExpressionHolder(this.expr);
aggregate = Aggregate.Factory(node.funcName.ToLower(), tmpHolder.ExpressionType, tmpHolder);
aggType = tmpHolder.ExpressionType;
}
}
// Rewrite the expression used for aggregation argument to aggregation reference.
int aggPos = this.exprInfo.AddAggregate(aggregate);
if (node.funcName.ToLower() == "avg")
{
this.expr = AggregateReferenceFactory.Create(typeof(double), aggPos, this.exprInfo.GroupByhashExprs.Count, this.exprInfo.Aggregates[aggPos]);
}
else if (node.funcName.ToLower() == "count")
{
this.expr = AggregateReferenceFactory.Create(typeof(int), aggPos, this.exprInfo.GroupByhashExprs.Count, this.exprInfo.Aggregates[aggPos]);
}
else if (node.funcName.ToLower() == "sum")
{
this.expr = AggregateReferenceFactory.Create(typeof(long), aggPos, this.exprInfo.GroupByhashExprs.Count, this.exprInfo.Aggregates[aggPos]);
}
else
{
this.expr = AggregateReferenceFactory.Create(aggType, aggPos, this.exprInfo.GroupByhashExprs.Count, this.exprInfo.Aggregates[aggPos]);
}
}
/// <summary>
/// AggregateFunc -> IDENTIFIER \( VarReference \)
/// </summary>
/// <param name="tokens"> Tokens to parse. </param>
/// <param name="position"> A position of a token. </param>
/// <returns> A non empty aggregate node. </returns>
static private Node ParseAggregateFunc(ref int position, List <Token> tokens)
{
// FuncName (
if (!((CheckToken(position, Token.TokenType.Identifier, tokens)) &&
(CheckToken(position + 1, Token.TokenType.LeftParen, tokens))))
{
return(null);
}
else
{
AggregateFuncNode aggregate = new AggregateFuncNode();
// Save the name of the function.
aggregate.funcName = tokens[position].strValue;
// It must inc by 2 because it was +1 moves it to left parent and another +1 moves it to next token.
position += 2;
if (CheckToken(position, Token.TokenType.Asterix, tokens))
{
if (aggregate.funcName.ToLower() != "count")
{
ThrowError("Expression parser", "Cannot call other aggregate functions with * except count.", position, tokens);
}
else
{
aggregate.next = new IdentifierNode("*");
position++;
}
}
else
{
aggregate.next = ParseVarReference(ref position, tokens);
}
// )
if (!CheckToken(position, Token.TokenType.RightParen, tokens))
{
ThrowError("Expression parser", "Expected ) .", position, tokens);
}
else
{
position++;
}
return(aggregate);
}
}
public void Visit(AggregateFuncNode node)
{
throw new NotImplementedException();
}