Linq 使用“和”运算符搜索文本

Question

我在下表中有一对多的关系

产品 [ProductId, Name(varchar)]

关键字 [KeywordId, Keyword(varchar)]

KeywordsToProducts[Id、ProductId、KeywordId]

假设搜索文本是“blue pro”。我需要使用运算符“和”搜索这两个关键字。 如果我执行以下操作：

string test="blue pro";
string[]words = test.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

var query = from p in Products 

join kp in KeywordsToProducts on p.ProductId equals kp.ProductId 

join kw in Keywords on kp.KeywordId equals kw.KeywordId 

where (words.All(x=>kw.Keyword.Contains(x)))

然后我什么都没有，因为字段关键字只包含一个单词。

如何加入“Keywrods.Keyword”数据库字段记录以便使用“and”运算符进行搜索？

Answer 1

如果您将每个匹配的 KeywordsToProducts 连接到 Keywords，您可以将它们收集起来并进行比较：

var query = from p in Products
            join kp in KeywordsToProducts on p.ProductId equals kp.ProductId into kpj
            let kws = (from kp in kpj join kw in Keywords on kp.KeywordId equals kw.KeywordId select kw.Keyword)
            where words.All(w => kws.Any(kw => kw.Contains(w)))
            select p;

但是，我认为如果您先分别执行 KeywordsToProducts 到 Keywords join 会更容易理解（并且可能更有效）（请注意，它显示连接表会更好地命名为 @987654328 @):

var kwToProducts = from kp in KeywordsToProducts
                   join kw in Keywords on kp.KeywordId equals kw.KeywordId
                   select new { kp.ProductId, kw.Keyword };

var query = from p in Products
            join kwp in kwToProducts on p.ProductId equals kwp.ProductId into kwpj
            where words.All(w => kwpj.Any(kwp => kwp.Keyword.Contains(w)))
            select p;

虽然我不是（不一定）喜欢提及它，但还要注意 EF 导航属性可以隐藏连接表并使此查询更容易。

应该是这样的：

var query = from p in Products
            where words.All(w => p.Keywords.Any(k => k.Contains(w)))
            select p;

我假设您打算使用String.Contains，以便用户可以输入部分关键字并仍然找到匹配项。如果你想要求所有的关键字都匹配，这里是相同的代码：

var query = from p in Products
            join kp in KeywordsToProducts on p.ProductId equals kp.ProductId into kpj
            let kws = (from kp in kpj join kw in Keywords on kp.KeywordId equals kw.KeywordId select kw.Keyword)
            where words.All(w => kws.Contains(w))
            select p;

拆分子连接：

var kwToProducts = from kp in KeywordsToProducts
                   join kw in Keywords on kp.KeywordId equals kw.KeywordId
                   select new { kp.ProductId, kw.Keyword };

var query = from p in Products
            join kwp in kwToProducts on p.ProductId equals kwp.ProductId into kwpj
            where words.All(w => kwpj.Select(kwp => kwp.Keyword).Contains(w))
            select p;

EF 导航属性：

var query = from p in Products
            where words.All(w => p.Keywords.Contains(w))
            select p;