Question

I’m trying to write Linq query on this Products table based on FacetTypes that need to be grouped by their Facet.

This is the table structure:

I get passed an array of facetTypeIds, say 9, 6, 52

FacetTypeId 9 has a name of "160" and is a Facet of "Size"     
FacetTypeId 6 has a name of "157" and is a Facet of "Size"     
FacetTypeId 52 has a name of "Cool Brand" and is a Facet of "Brand" 

They need to be constructed into a query that joins based on the facet, like this:

select * from products p
inner join (select productId from productFacets where facetTypeId in (9, 6)) 
    p1 on p1.productId = p.productId
inner join (select productId from productFacets where facetTypeId in (52)) 
    p2 on p2.productId = p.productId

The outcome is a result set that says:

Get me Products which have brand “Cool Brand” and Sizes of (160 or 157)

How would I go about creating a linq query that will dynamically build this?

I’m kinda stuck as to how this would be formed in linq.

EDIT:

This is the code I’ve sort of come up with however it feels pretty inefficient.

MyDbContext _context;

// Groups FacetTypeIds by Facet into int lists 
Dictionary<int, List<int>> createFacetGroup(int[] facetTypeIds)
{
    var facets = new Dictionary<int, List<int>>();

    var facetTypes = from ft in _context.FacetTypes where facetTypeIds.Contains(ft.FacetTypeId) select ft;
    foreach (var facetType in facetTypes)
    {
        if (facets.ContainsKey(facetType.Facet.FacetId))
            facets[facetType.Facet.FacetId].Add(facetType.FacetTypeId);
        else
            facets.Add(facetType.Facet.FacetId, new List<int> { facetType.FacetTypeId });
    }

    return facets;
}

public List<Product> FindProductsByGroupedFacetTypeIds(int[] facetTypeIds)
{
    var groupedFacetTypeIds = createFacetGroup(facetTypeIds);

    // this seem very inefficient but ToList needs to be called 
    // otherwise the results products in the foreach loop dont end 
    // up with the correct result set
    var products = _context.Products.ToList(); 

    foreach (var facetTypeIdGroup in groupedFacetTypeIds)
    {
        var facetTypeIdGroupArray = facetTypeIdGroup.Value.ToArray();
        products = (from p in products where p.FacetTypes.Any(x => facetTypeIdGroupArray.Contains(x.FacetTypeId)) select p).ToList();
    }

    return products;
}

Answer 1

In the interests of closing this question, i’ll submit my solution for this.

It’s not pretty but it works. If anyone else has a better solutions, I’d love to see it

MyDbContext _context;

// Groups FacetTypeIds by Facet into int lists 
Dictionary<int, List<int>> createFacetGroup(int[] facetTypeIds)
{
    var facets = new Dictionary<int, List<int>>();

    var facetTypes = from ft in _context.FacetTypes where facetTypeIds.Contains(ft.FacetTypeId) select ft;
    foreach (var facetType in facetTypes)
    {
        if (facets.ContainsKey(facetType.Facet.FacetId))
            facets[facetType.Facet.FacetId].Add(facetType.FacetTypeId);
        else
            facets.Add(facetType.Facet.FacetId, new List<int> { facetType.FacetTypeId });
    }

    return facets;
}

public List<Product> FindProductsByGroupedFacetTypeIds(int[] facetTypeIds)
{
    var groupedFacetTypeIds = createFacetGroup(facetTypeIds);

    // this seem very inefficient but ToList needs to be called 
    // otherwise the results products in the foreach loop dont end 
    // up with the correct result set
    var products = _context.Products.ToList(); 

    foreach (var facetTypeIdGroup in groupedFacetTypeIds)
    {
        var facetTypeIdGroupArray = facetTypeIdGroup.Value.ToArray();
        products = (from p in products where p.FacetTypes.Any(x => facetTypeIdGroupArray.Contains(x.FacetTypeId)) select p).ToList();
    }

    return products;
}