Question

我可以以及如何将一个字符串数组传递给Linq查询，以便数组的元素提供Where子句，如下面的示例所示？

如果其中一个数组为空，则查询应该仍然有效（只需忽略相应的where子句）。

查询是否会改变，而不是数组一，例如像List<string> brands，List<string> categories等列表？

    private IEnumerable<LatestReading> getLatestReadings(string[] brands, string[] categories)
    {
        return
           from reading in context.Readings
           join product in context.Products
           on reading.ProductId equals product.SkuCode
           // where product.Brand is one or more brands from string[] brands
           // where product.Category is one or more categories from string[] categories
           where reading.Date == lastReadingDate
           select new LatestReading
           {
               ProductId = reading.ProductId,
               Distributor = reading.Distributor,
               Price = reading.Price
           };
    }

Answer 1

private IEnumerable<LatestReading> getLatestReadings(string[] brands, string[] categories)
    {
        return
           from reading in context.Readings
           join product in context.Products
           on reading.ProductId equals product.SkuCode
           where (brands.Length == 0 || brands.Contains(product.Brand))
           where (categories.Length == 0 || categories.Contains(product.Category))
           where reading.Date == lastReadingDate
           select new LatestReading
           {
               ProductId = reading.ProductId,
               Distributor = reading.Distributor,
               Price = reading.Price
           };
    }

Answer 2

当然关键是使用Contains。正如您从链接中看到的，它适用于IEnumerable<T>，因此应回答问题的第二部分 - 您可以传递任何IEnumerable<string>，包括string[]，List<string>等。

虽然您可以使用another anwer中的技术，但它会生成一个奇怪的SQL查询（检查出来）。无论何时需要动态过滤，更好的方法是使用LINQ方法语法和动态Where链，就像这样

// Products subquery with optional filters
var products = context.Products.AsQueryable();
if (brands.Any())
    products = products.Where(product => brands.Contains(product.Brand);
if (categories.Any())
    products = products.Where(product => categories.Contains(product.Category);
// Now the main query (just use products instead of context.Products)
return
    from reading in context.Readings
    join product in products
        on reading.ProductId equals product.SkuCode
    where reading.Date == lastReadingDate
    select new LatestReading
    {
        ProductId = reading.ProductId,
        Distributor = reading.Distributor,
        Price = reading.Price
    };

将字符串数组作为参数传递给执行linq查询的方法

2 个答案: