public override VisitedExpression Visit(DbPropertyExpression expression)
{
/*
* Algorithm for finding the correct reference expression: "Collection"."Name"
* The collection is always a leaf InputExpression, found by lookup in _refToNode.
* The name for the collection is found using node.TopName.
*
* We must now follow the path from the leaf down to the root,
* and make sure the column is projected all the way down.
*
* We need not project columns at a current InputExpression.
* For example, in
* SELECT ? FROM <from> AS "X" WHERE "X"."field" = <value>
* we use the property "field" but it should not be projected.
* Current expressions are stored in _currentExpressions.
* There can be many of these, for example if we are in a WHERE EXISTS (SELECT ...) or in the right hand side of an Apply expression.
*
* At join nodes, column names might have to be renamed, if a name collision occurs.
* For example, the following would be illegal,
* SELECT "X"."A" AS "A", "Y"."A" AS "A" FROM (SELECT 1 AS "A") AS "X" CROSS JOIN (SELECT 1 AS "A") AS "Y"
* so we write
* SELECT "X"."A" AS "A", "Y"."A" AS "A_Alias<N>" FROM (SELECT 1 AS "A") AS "X" CROSS JOIN (SELECT 1 AS "A") AS "Y"
* The new name is then propagated down to the root.
*/
string name = expression.Property.Name;
string from = (expression.Instance.ExpressionKind == DbExpressionKind.Property)
? ((DbPropertyExpression)expression.Instance).Property.Name
: ((DbVariableReferenceExpression)expression.Instance).VariableName;
PendingProjectsNode node = _refToNode[from];
from = node.TopName;
while (node != null)
{
foreach (var item in node.Selects)
{
if (_currentExpressions.Contains(item.Exp))
continue;
var use = new StringPair(from, name);
if (!item.Exp.ColumnsToProject.ContainsKey(use))
{
var oldName = name;
while (item.Exp.ProjectNewNames.Contains(name))
name = oldName + "_" + NextAlias();
item.Exp.ColumnsToProject[use] = name;
item.Exp.ProjectNewNames.Add(name);
}
else
{
name = item.Exp.ColumnsToProject[use];
}
from = item.AsName;
}
node = node.JoinParent;
}
return new ColumnReferenceExpression { Variable = from, Name = name };
}
public override bool Equals(object obj)
{
if (obj == null)
{
return(false);
}
StringPair o = obj as StringPair;
if (o == null)
{
return(false);
}
return(_item1 == o._item1 && _item2 == o._item2);
}
public override VisitedExpression Visit(DbPropertyExpression expression)
{
/*
* Algorithm for finding the correct reference expression: "Collection"."Name"
* The collection is always a leaf InputExpression, found by lookup in _refToNode.
* The name for the collection is found using node.TopName.
*
* We must now follow the path from the leaf down to the root,
* and make sure the column is projected all the way down.
*
* We need not project columns at a current InputExpression.
* For example, in
* SELECT ? FROM <from> AS "X" WHERE "X"."field" = <value>
* we use the property "field" but it should not be projected.
* Current expressions are stored in _currentExpressions.
* There can be many of these, for example if we are in a WHERE EXISTS (SELECT ...) or in the right hand side of an Apply expression.
*
* At join nodes, column names might have to be renamed, if a name collision occurs.
* For example, the following would be illegal,
* SELECT "X"."A" AS "A", "Y"."A" AS "A" FROM (SELECT 1 AS "A") AS "X" CROSS JOIN (SELECT 1 AS "A") AS "Y"
* so we write
* SELECT "X"."A" AS "A", "Y"."A" AS "A_Alias<N>" FROM (SELECT 1 AS "A") AS "X" CROSS JOIN (SELECT 1 AS "A") AS "Y"
* The new name is then propagated down to the root.
*/
string name = expression.Property.Name;
string from = (expression.Instance.ExpressionKind == DbExpressionKind.Property)
? ((DbPropertyExpression)expression.Instance).Property.Name
: ((DbVariableReferenceExpression)expression.Instance).VariableName;
PendingProjectsNode node = _refToNode[from];
from = node.TopName;
while (node != null)
{
foreach (var item in node.Selects)
{
if (_currentExpressions.Contains(item.Exp))
{
continue;
}
var use = new StringPair(from, name);
if (!item.Exp.ColumnsToProject.ContainsKey(use))
{
var oldName = name;
while (item.Exp.ProjectNewNames.Contains(name))
{
name = oldName + "_" + NextAlias();
}
item.Exp.ColumnsToProject[use] = name;
item.Exp.ProjectNewNames.Add(name);
}
else
{
name = item.Exp.ColumnsToProject[use];
}
from = item.AsName;
}
node = node.JoinParent;
}
return(new ColumnReferenceExpression {
Variable = from, Name = name
});
}
