/// <summary>
/// This is called after a relational node's input has been visited, and the
/// input's sql statement cannot be reused. <see cref="Visit(DbProjectExpression)"/>
///
/// When the input's sql statement cannot be reused, we create a new sql
/// statement, with the old one as the from clause of the new statement.
///
/// The old statement must be completed i.e. if it has an empty select list,
/// the list of columns must be projected out.
///
/// If the old statement being completed has a join symbol as its from extent,
/// the new statement must have a clone of the join symbol as its extent.
/// We cannot reuse the old symbol, but the new select statement must behave
/// as though it is working over the "join" record.
/// </summary>
/// <param name="oldStatement"></param>
/// <param name="inputVarName"></param>
/// <param name="inputVarType"></param>
/// <param name="finalizeOldStatement"></param>
/// <param name="fromSymbol"></param>
/// <returns>A new select statement, with the old one as the from clause.</returns>
private SqlSelectStatement CreateNewSelectStatement(SqlSelectStatement oldStatement, string inputVarName, TypeUsage inputVarType, bool finalizeOldStatement, out Symbol fromSymbol)
{
fromSymbol = null;
// Finalize the old statement
if (finalizeOldStatement && oldStatement.Select.IsEmpty)
{
List <Symbol> columns = AddDefaultColumns(oldStatement);
// Thid could not have been called from a join node.
Debug.Assert(oldStatement.FromExtents.Count == 1);
// if the oldStatement has a join as its input, ...
// clone the join symbol, so that we "reuse" the
// join symbol. Normally, we create a new symbol - see the next block
// of code.
JoinSymbol oldJoinSymbol = oldStatement.FromExtents[0] as JoinSymbol;
if (oldJoinSymbol != null)
{
// Note: oldStatement.FromExtents will not do, since it might
// just be an alias of joinSymbol, and we want an actual JoinSymbol.
JoinSymbol newJoinSymbol = new JoinSymbol(inputVarName, inputVarType, oldJoinSymbol.ExtentList);
// This indicates that the oldStatement is a blocking scope
// i.e. it hides/renames extent columns
newJoinSymbol.IsNestedJoin = true;
newJoinSymbol.ColumnList = columns;
newJoinSymbol.FlattenedExtentList = oldJoinSymbol.FlattenedExtentList;
fromSymbol = newJoinSymbol;
}
}
if (fromSymbol == null)
{
if (oldStatement.OutputColumnsRenamed)
{
fromSymbol = new Symbol(inputVarName, inputVarType, oldStatement.OutputColumns);
}
else
{
// This is just a simple extent/SqlSelectStatement,
// and we can get the column list from the type.
fromSymbol = new Symbol(inputVarName, inputVarType);
}
}
// Observe that the following looks like the body of Visit(ExtentExpression).
SqlSelectStatement selectStatement = new SqlSelectStatement();
selectStatement.From.Append("( ");
selectStatement.From.Append(oldStatement);
selectStatement.From.AppendLine();
selectStatement.From.Append(") ");
return(selectStatement);
}
/// <summary>
/// This is called by the relational nodes. It does the following
/// <list>
/// <item>If the input is not a SqlSelectStatement, it assumes that the input
/// is a collection expression, and creates a new SqlSelectStatement </item>
/// </list>
/// </summary>
/// <param name="inputExpression"></param>
/// <param name="inputVarName"></param>
/// <param name="inputVarType"></param>
/// <param name="fromSymbol"></param>
/// <returns>A <see cref="SqlSelectStatement"/> and the main fromSymbol
/// for this select statement.</returns>
private SqlSelectStatement VisitInputExpression(DbExpression inputExpression, string inputVarName, TypeUsage inputVarType, out Symbol fromSymbol)
{
SqlSelectStatement result;
ISqlFragment sqlFragment = inputExpression.Accept(this);
result = sqlFragment as SqlSelectStatement;
if (result == null)
{
result = new SqlSelectStatement();
WrapNonQueryExtent(result, sqlFragment, inputExpression.ExpressionKind);
}
if (result.FromExtents.Count == 0)
{
// input was an extent
fromSymbol = new Symbol(inputVarName, inputVarType);
}
else if (result.FromExtents.Count == 1)
{
// input was Filter/GroupBy/Project/OrderBy
// we are likely to reuse this statement.
fromSymbol = result.FromExtents[0];
}
else
{
// input was a join.
// we are reusing the select statement produced by a Join node
// we need to remove the original extents, and replace them with a
// new extent with just the Join symbol.
JoinSymbol joinSymbol = new JoinSymbol(inputVarName, inputVarType, result.FromExtents);
joinSymbol.FlattenedExtentList = result.AllJoinExtents;
fromSymbol = joinSymbol;
result.FromExtents.Clear();
result.FromExtents.Add(fromSymbol);
}
return(result);
}
/// <summary>
/// This is called from <see cref="VisitJoinExpression"/>.
///
/// This is responsible for maintaining the symbol table after visiting
/// a child of a join expression.
///
/// The child's sql statement may need to be completed.
///
/// The child's result could be one of
/// <list type="number">
/// <item>The same as the parent's - this is treated specially.</item>
/// <item>A sql select statement, which may need to be completed</item>
/// <item>An extent - just copy it to the from clause</item>
/// <item>Anything else (from a collection-valued expression) -
/// unnest and copy it.</item>
/// </list>
///
/// If the input was a Join, we need to create a new join symbol,
/// otherwise, we create a normal symbol.
///
/// We then call AddFromSymbol to add the AS clause, and update the symbol table.
///
///
///
/// If the child's result was the same as the parent's, we have to clean up
/// the list of symbols in the FromExtents list, since this contains symbols from
/// the children of both the parent and the child.
/// The happens when the child visited is a Join, and is the leftmost child of
/// the parent.
/// </summary>
/// <param name="fromExtentFragment"></param>
/// <param name="result"></param>
/// <param name="input"></param>
/// <param name="fromSymbolStart"></param>
private void ProcessJoinInputResult(ISqlFragment fromExtentFragment, SqlSelectStatement result, DbExpressionBinding input, int fromSymbolStart)
{
Symbol fromSymbol = null;
if (result != fromExtentFragment)
{
// The child has its own select statement, and is not reusing
// our select statement.
// This should look a lot like VisitInputExpression().
SqlSelectStatement sqlSelectStatement = fromExtentFragment as SqlSelectStatement;
if (sqlSelectStatement != null)
{
if (sqlSelectStatement.Select.IsEmpty)
{
List <Symbol> columns = AddDefaultColumns(sqlSelectStatement);
if (IsJoinExpression(input.Expression) ||
IsApplyExpression(input.Expression))
{
List <Symbol> extents = sqlSelectStatement.FromExtents;
JoinSymbol newJoinSymbol = new JoinSymbol(input.VariableName, input.VariableType, extents);
newJoinSymbol.IsNestedJoin = true;
newJoinSymbol.ColumnList = columns;
fromSymbol = newJoinSymbol;
}
else
{
// this is a copy of the code in CreateNewSelectStatement.
// if the oldStatement has a join as its input, ...
// clone the join symbol, so that we "reuse" the
// join symbol. Normally, we create a new symbol - see the next block
// of code.
JoinSymbol oldJoinSymbol = sqlSelectStatement.FromExtents[0] as JoinSymbol;
if (oldJoinSymbol != null)
{
// Note: sqlSelectStatement.FromExtents will not do, since it might
// just be an alias of joinSymbol, and we want an actual JoinSymbol.
JoinSymbol newJoinSymbol = new JoinSymbol(input.VariableName, input.VariableType, oldJoinSymbol.ExtentList);
// This indicates that the sqlSelectStatement is a blocking scope
// i.e. it hides/renames extent columns
newJoinSymbol.IsNestedJoin = true;
newJoinSymbol.ColumnList = columns;
newJoinSymbol.FlattenedExtentList = oldJoinSymbol.FlattenedExtentList;
fromSymbol = newJoinSymbol;
}
else if (sqlSelectStatement.FromExtents[0].OutputColumnsRenamed)
{
fromSymbol = new Symbol(input.VariableName, input.VariableType, sqlSelectStatement.FromExtents[0].Columns);
}
}
}
else if (sqlSelectStatement.OutputColumnsRenamed)
{
fromSymbol = new Symbol(input.VariableName, input.VariableType, sqlSelectStatement.OutputColumns);
}
result.From.Append(" (");
result.From.Append(sqlSelectStatement);
result.From.Append(" )");
}
else if (input.Expression is DbScanExpression)
{
result.From.Append(fromExtentFragment);
}
else // bracket it
{
WrapNonQueryExtent(result, fromExtentFragment, input.Expression.ExpressionKind);
}
if (fromSymbol == null) // i.e. not a join symbol
{
fromSymbol = new Symbol(input.VariableName, input.VariableType);
}
AddFromSymbol(result, input.VariableName, fromSymbol);
result.AllJoinExtents.Add(fromSymbol);
}
else // result == fromExtentFragment. The child extents have been merged into the parent's.
{
// we are adding extents to the current sql statement via flattening.
// We are replacing the child's extents with a single Join symbol.
// The child's extents are all those following the index fromSymbolStart.
//
List <Symbol> extents = new List <Symbol>();
// We cannot call extents.AddRange, since the is no simple way to
// get the range of symbols fromSymbolStart..result.FromExtents.Count
// from result.FromExtents.
// We copy these symbols to create the JoinSymbol later.
for (int i = fromSymbolStart; i < result.FromExtents.Count; ++i)
{
extents.Add(result.FromExtents[i]);
}
result.FromExtents.RemoveRange(fromSymbolStart, result.FromExtents.Count - fromSymbolStart);
fromSymbol = new JoinSymbol(input.VariableName, input.VariableType, extents);
result.FromExtents.Add(fromSymbol);
// this Join Symbol does not have its own select statement, so we
// do not set IsNestedJoin
// We do not call AddFromSymbol(), since we do not want to add
// "AS alias" to the FROM clause- it has been done when the extent was added earlier.
symbolTable.Add(input.VariableName, fromSymbol);
}
}
