// protected override methods
protected override Expression Visit(Expression expression)
{
if (_candidates.Contains(expression))
{
string columnName;
if (expression.NodeType == (ExpressionType) PigExpressionType.Column)
{
var column = (ColumnExpression) expression;
ColumnExpression mapped;
if (_map.TryGetValue(column, out mapped))
{
return mapped;
}
if (_existingAliases.Contains(column.Alias))
{
columnName = GetUniqueColumnName(column.Name);
_columns.Add(new ColumnDeclaration(columnName, column));
mapped = new ColumnExpression(column.Type, _newAlias, columnName);
_map[column] = mapped;
_columnNames.Add(columnName);
return mapped;
}
// must be referring to outer scope
return column;
}
columnName = GetNextColumnName();
_columns.Add(new ColumnDeclaration(columnName, expression));
return new ColumnExpression(expression.Type, _newAlias, columnName);
}
return base.Visit(expression);
}
// protected override methods
protected override Expression VisitColumn(ColumnExpression node)
{
Dictionary<String, Expression> nameMap;
if (_map.TryGetValue(node.Alias, out nameMap))
{
Expression expr;
if (nameMap.TryGetValue(node.Name, out expr))
{
return Visit(expr);
}
throw new Exception("Reference to undefined column");
}
return node;
}
protected override Expression VisitColumn(ColumnExpression node)
{
WriteColumnName(node.Name);
return node;
}
/// <summary>
/// Rebind order expressions to reference a new alias and add to column declarations if necessary
/// </summary>
protected virtual BindResult RebindOrderings(IEnumerable<OrderByExpression> orderings, SourceAlias alias,
HashSet<SourceAlias> existingAliases,
IEnumerable<ColumnDeclaration> existingColumns)
{
List<ColumnDeclaration> newColumns = null;
var newOrderings = new List<OrderByExpression>();
foreach (OrderByExpression ordering in orderings)
{
Expression expr = ordering.Expression;
var column = expr as ColumnExpression;
if (column == null || (existingAliases != null && existingAliases.Contains(column.Alias)))
{
// check to see if a declared column already contains a similar expression
Int32 iOrdinal = 0;
if (existingColumns != null)
{
foreach (ColumnDeclaration decl in existingColumns)
{
var declColumn = decl.Expression as ColumnExpression;
if (decl.Expression == ordering.Expression ||
(column != null && declColumn != null && column.Alias == declColumn.Alias &&
column.Name == declColumn.Name))
{
// found it, so make a reference to this column
if (column != null) expr = new ColumnExpression(column.Type, alias, decl.Name);
break;
}
iOrdinal++;
}
// if not already projected, add a new column declaration for it
if (expr == ordering.Expression)
{
if (newColumns == null)
{
newColumns = new List<ColumnDeclaration>(existingColumns);
existingColumns = newColumns;
}
String colName = column != null ? column.Name : "c" + iOrdinal;
newColumns.Add(new ColumnDeclaration(colName, ordering.Expression));
expr = new ColumnExpression(expr.Type, alias, colName);
}
}
newOrderings.Add(new OrderByExpression(expr, ordering.Direction));
}
}
return existingColumns != null ? new BindResult(existingColumns, newOrderings) : null;
}
protected virtual Expression VisitColumn(ColumnExpression node)
{
return node;
}
// protected override methods
protected override Expression VisitColumn(ColumnExpression node)
{
MarkColumnAsUsed(node.Alias, node.Name);
return node;
}
