Question

I’ve a project which ask me to do such a BIG search engine but which is all dynamic. I mean I can have about 0 to 9 main “group” which have inside something like an infinite possibility of “where” with “OR” or “AND”. First thing we think was to use Dynamic Linq which provide a good alternative to build dynamic query. All this using EF with an homemade wrapper.

Probleme :
I’m not able to access to a “Collection”. I mean, I can easly access to a referenced object (Like Customer.State.StateName = “New-York” OR Custoemr.State.StateName = “Quebec” ) but I can’t find a way to acces to something like : “Customer.Orders.OrderID = 2 OR Customer.Orders.OrderID = 3”. I can easly figure out this its because its a collection, but how can I do this?

Please help me out!!

** Sorry for my english !!

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Update

I’m not clear enought I think, sorry its because im french…

My problem its because nothing is static. Its a candidat search engine for a recruting compagny that place candidats into an enterprise. In a page where manager can search candidat, he can “parse” by : Domain(s) (Jobs), City(ies) or many other that user have filled up when he register. All this in format (if it were in SQL) :

[…] WHERE (domaine.domainID = 3 OR domaine.domainID = 5 OR domaine.domainID = 23) AND (cities.cityID = 4, cities.city = 32) […]

So i can’t do this with a normal LINQ format like :

Candidat.Domaines.Where(domain => domain.DomainID == 3 || domain.DomainID == 5 || domain.DomainID == 23);

Even the operator in the paretheses are dynamic (“AND” or “OR”)! That why we trying to use Dynamic Linq because its a lot more flexible.

Hope its more easy to understand my problem …

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Update 2
Here’s my method

private string BuildDomainsWhereClause() {
        StringBuilder theWhere = new StringBuilder();

        if (this.Domaines.NumberOfIDs > 0) {
            theWhere.Append("( ");

            theWhere.Append(string.Format("Domaines.Where( "));
            foreach (int i in this.Domaines.ListOfIDs) {
                if (this.Domaines.ListOfIDs.IndexOf(i) > 0) {
                    theWhere.Append(string.Format(" {0} ", this.DispoJours.AndOr == AndOrEnum.And ? "&&" : "||"));
                }
                theWhere.Append(string.Format("DomaineId == {0}", i));
            }
            theWhere.Append(" ))");
        }

        return theWhere.ToString();
    }

It works great instead that it “Not return a boolean”. So how should I?
Error : “Expression of type ‘Boolean’ expected”.

At the end, it returns something like : “( Domaines.Where( DomaineId == 2 && DomaineId == 3 && DomaineId == 4 && DomaineId == 5 )).” which is added to my LINQ Query :

var queryWithWhere = from c in m_context.Candidats.Where(WHERE)
                                     select c;

Dont forget that there’s like 7 or 8 more “possible” added things to search in … Any ideas?

Answer 1

What you need to do here, is build a LambdaExpression (more specifically an Expression<Func<T, bool>>). You cannot use a string. You can build a simple expression like this:

ParameterExpression p = Expression.Parameter(typeof(Domaine), "domaine");
Expression<Func<Domaine, bool>> wherePredicate = 
  Expression.Lambda<Func<Domaine, bool>>(
    Expression.Or(
      Expression.Equal(
        Expression.Property(p, "DomainID"),
        Expression.Constant(10)),
      Expression.Equal(
        Expression.Property(p, "DomainID"),
        Expression.Constant(11))
      ), p);

i.e.,

domaine.DomainID = 10 || domaine.DomainID = 11

Not very readable if you need to do this by hand.

There’s a sample of a fully operational expression parser that will actually do this for you based on a string in C# Samples for Visual Studio 2008 at MSDN Code Gallery, under DynamicQuery. (The LinqDataSource control uses a slightly modified version of this sample internally.)