How can you update a Linq Expression with additional parameters?

Question

I have a Linq Expression, which may be altered depending on certain conditions. An example of what I would like to do (left blank the bit I am not sure about):

Answer 1

I think you want to combine filters this way:

var myFilters = new List>>();
myFilters.Add(c => c.Name.StartsWith("B"));
myFilters.Add(c => c.Orders.Count() == 3);
if (stranded)
{
  myFilters.Add(c => c.Friends.Any(f => f.Cars.Any())); //friend has car
}
Expression> filter = myFilters.AndTheseFiltersTogether();
IEnumerable thoseCustomers = Data.Get(filter);

This code will allow you to combine your filters.

    public static Expression> OrTheseFiltersTogether(params Expression>[] filters)
    {
        return filters.OrTheseFiltersTogether();
    }

    public static Expression> OrTheseFiltersTogether(this IEnumerable>> filters)
    {
        if (!filters.Any())
        {
            Expression> alwaysTrue = x => true;
            return alwaysTrue;
        }

        Expression> firstFilter = filters.First();

        var body = firstFilter.Body;
        var param = firstFilter.Parameters.ToArray();
        foreach (var nextFilter in filters.Skip(1))
        {
            var nextBody = Expression.Invoke(nextFilter, param);
            body = Expression.OrElse(body, nextBody);
        }
        Expression> result = Expression.Lambda>(body, param);
        return result;
    }


    public static Expression> AndTheseFiltersTogether(params Expression>[] filters)
    {
        return filters.AndTheseFiltersTogether();
    }

    public static Expression> AndTheseFiltersTogether(this IEnumerable>> filters)
    {
        if (!filters.Any())
        {
            Expression> alwaysTrue = x => true;
            return alwaysTrue;
        }
        Expression> firstFilter = filters.First();

        var body = firstFilter.Body;
        var param = firstFilter.Parameters.ToArray();
        foreach (var nextFilter in filters.Skip(1))
        {
            var nextBody = Expression.Invoke(nextFilter, param);
            body = Expression.AndAlso(body, nextBody);
        }
        Expression> result = Expression.Lambda>(body, param);
        return result;
    }