How do I dynamically create an Expression<Func<MyClass, bool>> predicate?

Question

How would I go about using an Expression Tree to dynamically create a predicate that looks something like...

(p.Length== 5) && (p.SomeOtherProperty == "hello")  

So that I can stick the predicate into a lambda expression like so...

q.Where(myDynamicExpression)... 

I just need to be pointed in the right direction.

Update: Sorry folks, I left out the fact that I want the predicate to have multiple conditions as above. Sorry for the confusion.

Answer 1

Original

Like so:

    var param = Expression.Parameter(typeof(string), "p");     var len = Expression.PropertyOrField(param, "Length");     var body = Expression.Equal(         len, Expression.Constant(5));      var lambda = Expression.Lambda<Func<string, bool>>(         body, param); 

---

Updated

re (p.Length== 5) && (p.SomeOtherProperty == "hello"):

var param = Expression.Parameter(typeof(SomeType), "p"); var body = Expression.AndAlso(        Expression.Equal(             Expression.PropertyOrField(param, "Length"),             Expression.Constant(5)        ),        Expression.Equal(             Expression.PropertyOrField(param, "SomeOtherProperty"),             Expression.Constant("hello")        )); var lambda = Expression.Lambda<Func<SomeType, bool>>(body, param); 

Answer 2

Use the predicate builder.

http://www.albahari.com/nutshell/predicatebuilder.aspx

Its pretty easy!