如何在Entity Framework中生成带OR条件的Join查询？

目标SQL #

想要实现带OR条件的内连接，对应的SQL语句如下：

SELECT COUNT(*) FROM Discounts
JOIN DiscountArticles ON Discounts.ID = DiscountArticles.Discount
JOIN Articles ON (DiscountArticles.Article = Articles.ID OR DiscountArticles.ArticleGroup = Articles.ArticleGroup)

参考方案中，Entity Framework无法直接实现上述内连接逻辑，可改用交叉连接实现，对应SQL如下：

SELECT COUNT(*) AS GroupCount FROM Discounts
JOIN DiscountArticles ON Discounts.ID = DiscountArticles.Discount
CROSS JOIN Articles
WHERE (Articles.ID = DiscountArticles.Article OR Articles.ArticleGroup = DiscountArticles.ArticleGroup)

EF查询尝试与问题 #

尝试用EF编写如下查询：

var query = from discounts in _dbContext.Discounts
    join discountArticles in _dbContext.DiscountArticles on discounts.Id equals discountArticles.Discount
    from article in _dbContext.Articles
    where article.Id == discountArticles.Article || article.ArticleGroup.Value == discountArticles.ArticleGroup.Value
    select new
    {
        ArticleId = article.Id,
        DiscountId = discounts.Id
    };

但生成的SQL自动添加了额外的NULL判断条件 OR (([a].[ArticleGroup] IS NULL) AND ([d0].[ArticleGroup] IS NULL))，导致查询结果数量远超预期。推测问题源于ArticleGroup是两个实体中的*Nullable Guid?*类型。

若添加非空判断：

where article.Id == discountArticles.Article ||
  article.ArticleGroup.HasValue && article.ArticleGroup == discountArticles.ArticleGroup

能得到正确结果，但生成的SQL条件更复杂：

WHERE ([a].[ID] = [d0].[Article]) OR (([a].[ArticleGroup] IS NOT NULL) AND ([a].[ArticleGroup] = [d0].[ArticleGroup]))

疑问 #

能否生成与目标SQL格式完全一致的查询，即WHERE条件为：

WHERE (Articles.ID = DiscountArticles.Article OR Articles.ArticleGroup = DiscountArticles.ArticleGroup)

内容的提问来源于stack exchange，提问作者Christian Gollhardt