Dynamic LINQ to SharePoint

Question

This question starts here: Dynamic LINQ to SharePoint and Projection

how to build dynamic LINQ to SharePoint expression like this(but store "Bill", "Sam" in array):

// Listing 1

// SPEntityModelDataContext generated with SPMetal
using (var db = new SPEntityModelDataContext("http://sharepoint/"))
{
    var res = db.OrgUnitToUser
        .Where(oo => (oo.User.Title == "Bill" || oo.User.Title == "Sam") 
            || [any condition we want])
        .ToList();
}

Using BuildOrExpressionEqual method we can finde all users with names stored in array:

// Listing 2

private static Expression<Func<TElement, bool>> BuildOrExpressionEqual<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)
{
    if (null == valueSelector)
        throw new ArgumentNullException("valueSelector");
    if (null == values)
        throw new ArgumentNullException("values");

    var p = valueSelector.Parameters.Single();

    if (!values.Any())
        return e => false;

    var equals =
        values.Select(value =>
            (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));


    var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

    return Expression.Lambda<Func<TElement, bool>>(body, p);
}


// usage

var names = new string[] {"Bill", "Sam"};

using (var db = new SPEntityModelDataContext("http://sharepoint/"))
{
    var res = db.OrgUnitToUser
        .Where(BuildOrExpressionEqual<OrgUnitToUserItem, string>(tt => tt.User.Title, names))
        .ToList();
}

But how to add [any condition we want] (see Listing 1)?

Answer 1

Try using the LINQ Dynamic Query Library. A class file (Dynamic.cs) is provided by MS in their C# samples. Reference that in your project. It extends LINQ so that we can use strings for Where expressions. This lets us compose query at runtime.

Here is an article which I found to be helpful when I was working on a similar problem: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx