实施“不存在的地方".使用NHibernate QueryOver [英] Implementing "where not exists" with NHibernate QueryOver

问题描述

在NHibernate中使用新的QueryOver API，我需要执行以下操作:

Using the new QueryOver API in NHibernate, I need to do something equivalent of:

select c.*
from Category c
where not exists (
    select *
    from CategoryProduct cp
    where cp.CategoryID = c.Id
    and cp.ProductID = 'DogFood'
)

换句话说:给我不包含狗食的所有类别".

In other words: "Give me all categories that doesn't contain dog food".

我最初的想法是:

IEnumerable<Category> FindCategoriesWithoutProduct(Product product)
{
    return _session
        .QueryOver<Category>()
        .Where(c => c.Products.Contains(product))
        .List();
}

但是，这会使NHibernate.Impl.ExpressionProcessor在System.Collections.Generic.ICollection<T>.Contains()上被无法识别的方法调用"炸毁.

However, this makes NHibernate.Impl.ExpressionProcessor blow up with an "unrecognised method call" on System.Collections.Generic.ICollection<T>.Contains().

我认为还必须采用其他方法，可能涉及到ICriterion，但是我在这里和Google上的搜索均未返回任何有用的信息.

I assume there must be some other way to do this, probably involving an ICriterion, but my searches here and on Google have returned nothing useful.

推荐答案

我只是遇到了同样的问题，可能的解决方法是:

I'm just running in the same problem, and possible solution is:

Category aliasCategory = null;
CategoryProduct aliasCategoryProduct = null;

var qcp = QueryOver.Of<CategoryProduct>(() => aliasCategoryProduct)
          .Where(() => aliasCategoryProduct.ProductID == "DogFood")
          .Where(() => aliasCategory.Id == aliasCategoryProduct.CategoryID)
          .DetachedCriteria;

return _session.QueryOver<Category>(() => aliasCategory)
               .Where(Subqueries.NotExists(qcp));

它在我的类似条件下工作.

It works on my similar criteria.

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