c# - 使用 Linq to Entities 按需“或”，我该怎么做？

Question

我有以下按需执行“AND”的查询：

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.
}

那么，我怎样才能执行相同的查询但按需执行“OR”（以便查询有意义）？

Answer 1

使用包含：

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

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

Answer 2

您可以使用INfor LINQ 的传真：

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

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

它基本上是在说：

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

Answer 3

要么使用ContainsBrad 和 Joe 所写的方法，要么（如果不可能）使用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);