/// <summary>
/// Returns the member expressions in the expression hierarchy of the <paramref name="expression"/>
/// </summary>
/// <param name="expression">The expression to search</param>
/// <returns>A collection of <see cref="MemberExpression"/> objects</returns>
internal static IEnumerable <MemberExpression> GetMemberExpressions(this Expression expression)
{
List <MemberExpression> members = new();
VisitorHelper.VisitMembers(expression, (expr, recurse) =>
{
members.Add(expr);
return(recurse(expr));
});
return(members);
}
/// <summary>
/// Walk the expression and compute all the subtrees that are not dependent on any
/// of the expressions parameters.
/// </summary>
/// <param name="expression">The expression to analyze.</param>
/// <returns>A collection of all the expression subtrees that are independent from the expression parameters.</returns>
internal static List <Expression> FindIndependentSubtrees(this Expression expression)
{
List <Expression> subtrees = new();
// The dependenty and isMemberInit flags are used to communicate between different layers
// of the recursive visitor.
bool dependent = false;
bool isMemberInit = false;
// Walk the tree, finding the independent subtrees
VisitorHelper.VisitAll(expression, (expr, recurse) =>
{
if (expr != null)
{
bool parentIsDependent = dependent;
bool parentIsMemberInit = isMemberInit;
// Set flags
dependent = false;
isMemberInit = expr is MemberInitExpression;
// Recurse
recurse(expr);
// If nothing in my subtree is dependent
if (!dependent)
{
// A NewExpression itself will appear to be indepentt, but if the parent is a MemberInitExpression,
// then the NewExpression can't be evaluated by itself. The MemberInitExpression will determine
// if the full expression is dependent or not, so don't check it here.
if (expr is NewExpression newExpression && parentIsMemberInit)
{
return(expr);
}
// The current node is independent if it's not related to the parameter and it's not the constant query root.
ConstantExpression constant = expr as ConstantExpression;
if (expr.NodeType == ExpressionType.Parameter || (constant?.Value is IQueryable))
{
dependent = true;
}
else
{
subtrees.Add(expr);
}
}