Filter comma separated list for multiple matches using LINQ

[nfplee]

My application has the following entities:

public class Product {
    public virtual int Id { get; set; }
    public virtual IList<ProductFieldValue> FieldValues { get; set; } = new List<ProductFieldValue>();
}

public class ProductFieldValue {
    public virtual Product Product { get; set; }
    public virtual Field Field { get; set; }
    public virtual string Value { get; set; } // This is a comma separated list of values.
}

public class Field {
    public virtual int Id { get; set; }
}

I'd lke to retrieve a list of products filtered by the field values. For example say I have the following dictionary to filter against (where the key is the field id and the value is the values I'd like to filter by):

var filters = new Dictionary<int, string[]>() {
    { 1, new[] { "A", "B" } },
    { 2, new[] { "X" } }
};

I could say something like:

var query = _session.Query<Product>();

foreach (var field in filters) {
    foreach (var value in field.Value) {
        query = query.Where(p => p.FieldValues.Any(fv => fv.Field.Id == field.Key && (fv.Value.StartsWith(value + ",") || fv.Value.Contains(", " + value + ",") || fv.Value.EndsWith(", " + value) || fv.Value.Equals(value))));
    }
}

var results = await query.ToListAsync();

Whilst this executes fine, it will only returns back a matching product if it matches every potential value in the filter. Using the example above it would only return back products which matched both "A" and "B". Ideally I'd like this to match any products which match any of the field values. Therefore I changed my query to the following:

var query = _session.Query<Product>();

foreach (var field in filters) {
    query = query.Where(p => p.FieldValues.Any(fv => fv.Field.Id == field.Key && field.Value.Any(fv2 => fv.Value!.StartsWith(fv2 + ",") || fv.Value.Contains(", " + fv2 + ",") || fv.Value.EndsWith(", " + fv2) || fv.Value.Equals(fv2))));
}

var results = await query.ToListAsync();

However this throws back the error "System.NotSupportedException: ': ( : p2 )'". I'm also slighty concerned about the performance of this.

I know the obvious solution is to add a record in the ProductFieldValue entity's table for each value (instead of using a comma separated list) but unfortunately this is not possible as this structure is set in stone.

If anyone has any further suggestions which will allow me do this filter using LINQ in the most efficient way I'd really appreciate it.