Extend IQueryable<T> Where() as OR instead of AND relationship

Solution 1:

I'm assuming the different parts of the query are only known at runtime, i.e. you can't just use || in a where...

One lazy option is Concat - but this tends to lead to poor TSQL etc; however, I tend to be inclined to write custom Expressions instead. The approach to take depends on what the provider is, as LINQ-to-SQL supports different options to EF (for example) - which has a genuine impact here (since you can't use sub-expressions with EF). Can you tell us which?

Here's some code that should work with LINQ-to-SQL; if you build an array (or list, and call .ToArray()) of expressions, it should work fine; example is LINQ-to-Objects, but should still work:

    static void Main()
    {
        var data = (new[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }).AsQueryable();

        var predicates = new List<Expression<Func<int, bool>>>();
        predicates.Add(i => i % 3 == 0);
        predicates.Add(i => i >= 8);           

        foreach (var item in data.WhereAny(predicates.ToArray()))
        {
            Console.WriteLine(item);
        }
    }

    public static IQueryable<T> WhereAny<T>(
        this IQueryable<T> source,
        params Expression<Func<T,bool>>[] predicates)
    {
        if (source == null) throw new ArgumentNullException("source");
        if (predicates == null) throw new ArgumentNullException("predicates");
        if (predicates.Length == 0) return source.Where(x => false); // no matches!
        if (predicates.Length == 1) return source.Where(predicates[0]); // simple

        var param = Expression.Parameter(typeof(T), "x");
        Expression body = Expression.Invoke(predicates[0], param);
        for (int i = 1; i < predicates.Length; i++)
        {
            body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
        }
        var lambda = Expression.Lambda<Func<T, bool>>(body, param);
        return source.Where(lambda);
    }

Solution 2:

Use PredicateBuilder<T>. It's probably what you want.