/// <summary>
/// Constructs a join propagator.
/// </summary>
/// <param name="left">Result of propagating changes in the left input to the join</param>
/// <param name="right">Result of propagating changes in the right input to the join</param>
/// <param name="node">Join operator in update mapping view over which to propagate changes</param>
/// <param name="parent">Handler of propagation for the entire update mapping view</param>
internal JoinPropagator(ChangeNode left, ChangeNode right, DbJoinExpression node, Propagator parent)
{
EntityUtil.CheckArgumentNull(left, "left");
EntityUtil.CheckArgumentNull(right, "right");
EntityUtil.CheckArgumentNull(node, "node");
EntityUtil.CheckArgumentNull(parent, "parent");
m_left = left;
m_right = right;
m_joinExpression = node;
m_parent = parent;
Debug.Assert(DbExpressionKind.LeftOuterJoin == node.ExpressionKind || DbExpressionKind.InnerJoin == node.ExpressionKind, "(Update/JoinPropagagtor/JoinEvaluator) " +
"caller must ensure only left outer and inner joins are requested");
// Retrieve propagation rules for the join type of the expression.
if (DbExpressionKind.InnerJoin == m_joinExpression.ExpressionKind)
{
m_insertRules = s_innerJoinInsertRules;
m_deleteRules = s_innerJoinDeleteRules;
}
else
{
m_insertRules = s_leftOuterJoinInsertRules;
m_deleteRules = s_leftOuterJoinDeleteRules;
}
// Figure out key selectors involved in the equi-join (if it isn't an equi-join, we don't support it)
JoinConditionVisitor.GetKeySelectors(node.JoinCondition, out m_leftKeySelectors, out m_rightKeySelectors);
// Find the key selector expressions in the left and right placeholders
m_leftPlaceholderKey = ExtractKey(m_left.Placeholder, m_leftKeySelectors, m_parent);
m_rightPlaceholderKey = ExtractKey(m_right.Placeholder, m_rightKeySelectors, m_parent);
}
/// <summary>
/// Determine properties from the left and right inputs to an equi-join participating
/// in predicate.
/// </summary>
/// <remarks>
/// The property definitions returned are 'aligned'. If the join predicate reads:
/// <code>
/// a = b AND c = d AND e = f
/// </code>
/// then the output is as follows:
/// <code>
/// leftProperties = {a, c, e}
/// rightProperties = {b, d, f}
/// </code>
/// See Walker class for an explanation of this coding pattern.
/// </remarks>
static internal void GetKeySelectors(DbExpression joinCondition, out ReadOnlyCollection <DbExpression> leftKeySelectors, out ReadOnlyCollection <DbExpression> rightKeySelectors)
{
EntityUtil.CheckArgumentNull(joinCondition, "joinCondition");
// Constructs a new predicate visitor, which implements a visitor for expression nodes
// and returns no values. This visitor instead builds up a list of properties as leaves
// of the join predicate are visited.
JoinConditionVisitor visitor = new JoinConditionVisitor();
// Walk the predicate using the predicate visitor.
joinCondition.Accept(visitor);
// Retrieve properties discovered visiting predicate leaf nodes.
leftKeySelectors = visitor.m_leftKeySelectors.AsReadOnly();
rightKeySelectors = visitor.m_rightKeySelectors.AsReadOnly();
Debug.Assert(leftKeySelectors.Count == rightKeySelectors.Count,
"(Update/JoinPropagator) The equi-join must have an equal number of left and right properties");
}
