//extend the where when we are working with indexable collections!
public static IEnumerable <T> Where <T>
(
this XbimIndexedCollection <T> sourceCollection,
Expression <Func <T, bool> > expr
)
{
//our indexes work from the hash values of that which is indexed, regardless of type
int? hashRight = null;
bool noIndex = true;
//indexes only work on equality expressions here
if (expr.Body.NodeType == ExpressionType.Equal)
{
//Equality is a binary expression
BinaryExpression binExp = (BinaryExpression)expr.Body;
//Get some aliases for either side
Expression leftSide = binExp.Left;
Expression rightSide = binExp.Right;
hashRight = GetHashRight(leftSide, rightSide);
//if we were able to create a hash from the right side (likely)
MemberExpression returnedEx = GetIndexablePropertyOnLeft(leftSide, sourceCollection);
if (hashRight.HasValue && returnedEx != null)
{
//cast to MemberExpression - it allows us to get the property
MemberExpression propExp = returnedEx;
string property = propExp.Member.Name;
IEnumerable <T> values = sourceCollection.GetValues(property, hashRight.Value);
if (values != null)
{
foreach (T item in values)
{
yield return(item);
}
noIndex = false; //we found an index, whether it had values or not is another matter
}
}
}
if (noIndex) //no index? just do it the normal slow way then...
{
IEnumerable <T> sourceEnum = sourceCollection.AsEnumerable();
IEnumerable <T> result = sourceEnum.Where(expr.Compile());
foreach (T resultItem in result)
{
yield return(resultItem);
}
}
}
private static MemberExpression GetIndexablePropertyOnLeft <T>(Expression leftSide,
XbimIndexedCollection <T> sourceCollection)
{
MemberExpression mex = leftSide as MemberExpression;
if (leftSide.NodeType == ExpressionType.Call)
{
MethodCallExpression call = leftSide as MethodCallExpression;
if (call.Method.Name == "CompareString")
{
mex = call.Arguments[0] as MemberExpression;
}
}
return(mex);
}
