CODEWITHSUNDEEP
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markpcasey
markpcasey

Reputation: 559

Chaining Where Clauses Does Not Return Results

I have a search method that takes a list of ID's and I wish to restrict the query based on the ID's.

Param: IEnumerable filterType

foreach (int id in filterType)
{
    query = query.Where(q => q.Item1 == id);
}

If I try:

foreach (int id in filterType)
{
    query = query.Where(q => q.Item1 != id);
}

It seems to work.

Does anyone know why?

Thanks in advance.

Upvotes: 1

Views: 130

Answers (2)

R. Martinho Fernandes
R. Martinho Fernandes

Reputation: 234664

By doing query = query.Where(q => q.Item1 == id);, you're effectively building a query similar to the following:

query.Where(q => q.Item1 == id1)
     .Where(q => q.Item1 == id2)
     .Where(q => q.Item1 == id3)
     .Where(q => q.Item1 == id4);

Which obviously won't return results: an item cannot have two different IDs.

You probably want:

query.Where(q = filterType.Contains(q.Item1));

Upvotes: 2

Jon Skeet
Jon Skeet

Reputation: 1503290

Multiple where clauses are effectively "AND-ed" together - so if your filterType list had 5 and 10 in, you'd be saying that Item1 had to be both 5 and 10, which it can't be simultaneously.

I suspect you actually want:

query = query.Where(q => filterType.Contains(q.Item1));

In other words, where Item1 matches one of the values in filterType. (You might also want to consider the case where filterType is empty. Should that match everything or nothing?)

Upvotes: 4

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