EF核心扩展，方法不起作用

Question

我为过滤查询创建了新的IQueryable扩展方法。在手动添加到我的查询的扩展方法内容中，它正在工作。但是它不适用于IQueryable扩展方法。怎么发生的？

我的扩展IQueryables：

 public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate)
    {
        if (condition)
            return source.Where(predicate);
        else
            return source;
    }


    public static IQueryable<ProductPrice> GetDynamicWhere(this IQueryable<ProductPrice> source,List<ProductFilterModel> productFilters)
    {
        Func<string, object> GetValue = (string key) => productFilters.Where(y => y.key == key).Select(x => x.value).FirstOrDefault();

        var minPrice = GetValue("min-price");
        var maxPrice = GetValue("max-price");

        source.Where(x=>x.IsDeleted==false)
              .WhereIf(minPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() >= Convert.ToInt32(minPrice.ToString()))
              .WhereIf(maxPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() <= Convert.ToInt32(minPrice.ToString()));

        return source;
    }

---

不起作用，此查询返回了所有数据：

MyDbContext.ProductPrices
           //.AsQueryable()
           .GetDynamicWhere(filter)
           .Include(x => x.ProductVariant.Product)
           .Include(x => x.ProductVariant.Variant)
           .Include(x => x.ProductVariant.Variant.VariantType)
           .ToList();

---

但是这正在起作用（GetDynamicWhere扩展方法中的相同代码）：

 MyDbContext.ProductPrices
            .Where(x=>x.IsDeleted==false)
            .WhereIf(minPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() >= Convert.ToInt32(minPrice.ToString()))
            .WhereIf(maxPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() <= Convert.ToInt32(minPrice.ToString()))
            .ToList();

Answer 1

相反，您可以这样做：

return source.Where(x=>x.IsDeleted==false)
          .WhereIf(minPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() >= Convert.ToInt32(minPrice.ToString()))
          .WhereIf(maxPrice != null, x => x.ProductVariant.ProductPrices.Where(y => y.IsDeleted == false).Select(y => y.Price).FirstOrDefault() <= Convert.ToInt32(minPrice.ToString()));