linq-to-sql combine expressions

Question

Is there any way I can combine list of expressions into one? I have List<Expression<Child, bool>> expList and trying to combine into one (AndAlso) and get

Expression<Child, bool> combined = Combine(expList);

Intended usage for combined expression is this:

//type of linqFilter is IQueryable<Parent>
linqFilter = linqFilter.SelectMany(p => p.Child).
         Where(combined).Select(t=> t.Parent); 

I am trying something like this:

var result = expList.Cast<Expression>().
Aggregate((p1, p2) => Expression.AndAlso(p1, p2));

But getting an exception

{"The binary operator AndAlso is not defined for the types 'System.Func`2[Child,System.Boolean]' and 'System.Func`2[Child,System.Boolean]'."}

Answer 1

Try this its a builder so you would have to recursively call it for each in expList

public Expression<Func<T, bool>> Combine<T>(Expression<Func<T, Boolean>> first, Expression<Func<T, Boolean>> second)
{

   var toInvoke= Expression.Invoke(second, first.Parameters.Cast<Expression>());

   return (Expression.Lambda<Func<T, Boolean>>(Expression.AndAlso(first.Body, toInvoke), first.Parameters));

}