“或”按需使用 Linq 到实体，我该怎么做？

Question

I have the following query that performs a "AND" on-demand:

var products = // Selecting a list of products in anywhere based in a filter...

foreach (var product in products)
{
    query = query.Where(p => p.Code == product.Code); // with this way, this query make no sense because this happens in any scenario, never a code can be more than one code.
}

So, how can i do the same query but performing a "OR" on-demand (so that the query makes sense)?

Answer 1

Using Contains :

var codes = products.Select(x => x.Code).ToArray();

query.Where(p => codes.Contains(p.Code));

Answer 2

You can use the facsimile of an IN for LINQ:

var productCodeList = products.Select(p => p.Code).ToList();

query = query.Where(p => productCodeList.Contains(p.Code));

It's basically saying:

SELECT   *
FROM     products
WHERE    code IN (<list_of_codes>)

Answer 3

Either use the Contains method ad Brad and Joe wrote, or (when that's not possible) use the PredicateBuilder:

var predicate = PredicateBuilder.False<Product>();

foreach (var product in products)
{
    var code = product.Code;
    predicate = predicate.Or(p => p.Code == code);
}

var products dataContext.Products.Where(predicate);