Question

Lets say i have a form which have the following :

Name:TextBox
Email:TextBox
Age:TextBox

now i want to Get customers Collection based on this filter textboxs

so i want to to use something like :

List<customer> customers = getCustomerswhere(c=>c.name == txtName.Text && Email == txtEmail.Text);

now of course i dont know which he will fill and which he wont so

if (txtName.Text.trim() != "")
   //something like c=>c.Name == txtName.text;
if (txtEmail.Text.trim() != "")
   //something like and c=>c.Email == txtEmail.text;

how do i do this ! i cant concatenate lambda expressions , i know i can use dynamic expressions but i think there is easier way ? any idea how to implement this ?

---

ok i tried this:

        Func<Customer,bool > a = (bb) => bb.fullName == "asdfsd";
        Func<Customer, bool> b = c => c.lastName == "sdas";
        Func<Customer, bool> cc = c => a(c) && b(c);

now comes another problem

the method im passing CC to is expecting Expression<Func<T, bool>> expression

so it doesnt work gives me compile time error cant convert between types!

Answer 1

Here is how i Implemented it:

   public class LambdaCriteries<T> : List<Expression<Func<T, bool>>>
{
    public Expression<Func<T, bool>> GetFinalLambdaExpression()
    {
        var par = Expression.Parameter(typeof(T));
        var intial = Expression.Invoke(this.First(),par);
        var sec = Expression.Invoke(this.Skip(1).First(),par);
        BinaryExpression binaryExpression = Expression.And(intial, sec);
        if (this.Count> 2)
        {
            foreach (var ex in this.ToList().Skip(2))
            {
                binaryExpression = Expression.And(binaryExpression, Expression.Invoke(ex, par));
            }
            return Expression.Lambda<Func<T, bool>>(binaryExpression,par);
        }
        else
        {
            return Expression.Lambda<Func<T, bool>>(binaryExpression,par);
        }

    }
}

and to use it :

           if(txtId.text != "")
                criteries.Add(v => v.Id == int.Parse(txtId.text));
           if(txtName.text != "")
                criteries.Add(v => v.Name == txtId.text);

and final expression :

var finalexp = criteries.GetFinalLambdaExpression();