Question

Is there any way I can rewrite this piece of code so that I don’t have to duplicate the join and where clauses in multiple queries?

if (categoryId > 0)
{
    query = from p in _productRepository.Table
            from pv in p.ProductVariants.DefaultIfEmpty()
            from pc in p.ProductCategories.Where(pc => pc.CategoryId == categoryId)
            join psa in _productSpecificationAttributeRepository.Table on p.Id equals psa.ProductId
            join sao in _specificationAttributeOptionRepository.Table on psa.SpecificationAttributeOptionId equals sao.Id
            join sa in _specificationAttributeRepository.Table on sao.SpecificationAttributeId equals sa.Id
            where p.Published && pv.Published && !p.Deleted && psa.AllowFiltering &&
            (!pv.AvailableStartDateTimeUtc.HasValue || pv.AvailableStartDateTimeUtc.Value < nowUtc) &&
            (!pv.AvailableEndDateTimeUtc.HasValue || pv.AvailableEndDateTimeUtc.Value > nowUtc)
            select new {sa, sao};
}
else if (brandId > 0)
{
    query = from p in _productRepository.Table
            from pv in p.ProductVariants.DefaultIfEmpty()
            from pb in p.ProductBrands.Where(pb => pb.BrandId == brandId)
            join psa in _productSpecificationAttributeRepository.Table on p.Id equals psa.ProductId
            join sao in _specificationAttributeOptionRepository.Table on psa.SpecificationAttributeOptionId equals sao.Id
            join sa in _specificationAttributeRepository.Table on sao.SpecificationAttributeId equals sa.Id
            where p.Published && pv.Published && !p.Deleted && psa.AllowFiltering &&
            (!pv.AvailableStartDateTimeUtc.HasValue || pv.AvailableStartDateTimeUtc.Value < nowUtc) &&
            (!pv.AvailableEndDateTimeUtc.HasValue || pv.AvailableEndDateTimeUtc.Value > nowUtc)
            select new {sa, sao};
}

//only distinct attributes (group by ID)
query = from x in query
        group x by x.sao.Id into xGroup
        orderby xGroup.Key
        select xGroup.FirstOrDefault();

The only thing that changes between the 2 queries is this join:

from pc in p.ProductCategories.Where(pc => pc.CategoryId == categoryId)

with this join:

from pb in p.ProductBrands.Where(pb => pb.BrandId == brandId)

Answer 1

After a good night’s sleep i came up with the solution, which is very simple – split the query in 2 parts:

if (categoryId > 0)
{
    q1 = from p in _productRepository.Table
         from pc in p.ProductCategories.Where(pc => pc.CategoryId == categoryId)
         select p;
}
else if (brandId > 0)
{
    q1 = from p in _productRepository.Table
         from pb in p.ProductBrands.Where(pb => pb.BrandId == brandId)
         select p;
}
var query = from p in q1
            from pv in p.ProductVariants.DefaultIfEmpty()
            join psa in _productSpecificationAttributeRepository.Table on p.Id equals psa.ProductId
            join sao in _specificationAttributeOptionRepository.Table on psa.SpecificationAttributeOptionId equals sao.Id
            join sa in _specificationAttributeRepository.Table on sao.SpecificationAttributeId equals sa.Id
            where p.Published && pv.Published && !p.Deleted && psa.AllowFiltering &&
            (!pv.AvailableStartDateTimeUtc.HasValue || pv.AvailableStartDateTimeUtc.Value < nowUtc) &&
            (!pv.AvailableEndDateTimeUtc.HasValue || pv.AvailableEndDateTimeUtc.Value > nowUtc)
            select new { sa, sao };

//only distinct attributes (group by ID)
query = from x in query
        group x by x.sao.Id into xGroup
        orderby xGroup.Key
        select xGroup.FirstOrDefault();