public static void Main()
{
Thingy t = new Thingy();
// Note execution is deferred until enumeration (in this case Count())
var allData = t.GetData();
Console.WriteLine("All Data count: {0}", allData.Count());
// Select only valid records from data set (should be 2)
var isValid = t.GetData();
isValid = isValid.Where(w => w.IsValid);
Console.WriteLine("IsValid count: {0}", isValid.Count());
// select only records with an ID greater than 1 (should be 2)
var gt1 = t.GetData();
gt1 = gt1.Where(w => w.Id > 1);
Console.WriteLine("gt 1 count: {0}", gt1.Count());
// Here we're combining in a single statement, IsValid and gt 1 (should be 1)
var isValidAndIdGt1 = t.GetData();
isValidAndIdGt1 = isValidAndIdGt1.Where(w => w.IsValid && w.Id > 1);
Console.WriteLine("IsValid and gt 1 count: {0}", isValidAndIdGt1.Count());
// This is the same query as the one directly above, just broken up (could perhaps be some if logic in there to determine if to add the second Where
// Note this is how you're doing it in your question (and it's perfectly valid (should be 1)
var isValidAndIdGt1Appended = t.GetData();
isValidAndIdGt1Appended = isValidAndIdGt1Appended.Where(w => w.IsValid);
isValidAndIdGt1Appended = isValidAndIdGt1Appended.Where(w => w.Id > 1);
Console.WriteLine("IsValid and gt 1 count w/ appended where: {0}", isValidAndIdGt1Appended.Count());
// This is the same query as the one directly above, but note we are executing the query twice
var isValidAndIdGt1AppendedTwice = t.GetData();
isValidAndIdGt1AppendedTwice = isValidAndIdGt1AppendedTwice.Where(w => w.IsValid);
Console.WriteLine("IsValid and gt 1 count w/ appended where executing twice: {0}", isValidAndIdGt1AppendedTwice.Count()); // 2 results are valid
isValidAndIdGt1AppendedTwice = isValidAndIdGt1AppendedTwice.Where(w => w.Id > 1);
Console.WriteLine("IsValid and gt 1 count w/ appended where executing twice: {0}", isValidAndIdGt1AppendedTwice.Count()); // 1 result is both valid and id gt 1
// This is one of the things you were asking about - note that without assigning the additional Where criteria to the Iqueryable, you do not get the results of the where clause, but the original query - in this case there are no appended where conditions on the t.GetData() call, so you get the full result set.
var notReallyValid = t.GetData();
notReallyValid.Where(w => w.Name == "this name definitly does not exist");
Console.WriteLine("where clause not correctly appended count: {0}", notReallyValid.Count());
// vs
var validUse = t.GetData();
validUse = validUse.Where(w => w.Name == "this name definitly does not exist");
Console.WriteLine("valid use count: {0}", validUse.Count());
}
