How to define a softbody object that is partly flexible?

[josemendez]

Do you have any ideas to deal with collision detection against the non-softbody parts of the object? Just adding mesh collider doesn't work right?

If you're using this for a character, the usual approach is to add primitive colliders (typically spheres or capsules) parented to the character's limbs. If your case is different, a MeshCollider might be a better approach, I can't know for sure.

Is it possible that non-softbody parts is defined as Rigidbody and softbody parts is attached to the Rigidbody? (actually I don't know how to do by script thought...)

Yes, this is what the ElasticCharacter sample scene does. You just add an attachment between some of the softbody particles and the rigidbody. See:
http://obi.virtualmethodstudio.com/manua...ments.html
http://obi.virtualmethodstudio.com/manua...ments.html

kind regards,