CRED plugin allows you to build forms that create child posts and set parents for these posts, supporting the parent-child relationship functionality from Types plugin.
When you ask for help or report issues, make sure to tell us the structure of your content and the relationship between the content types.
Problem: I would like to create a one-to-many relationship between Users and a post type.
Solution: You can either create a proxy post type for Users and relate that proxy post type using Toolset's Post Relationships feature, or you can create a custom usermeta field that stores a reference to the related post by ID.
