'Two different tables, both fetch information of another one

I have two similar tables Projects and Ideas So I have a Project with his unique PID: 1, and for example an Idea with the same unique IID: 1. I'm trying to add another table called "Comments" that it's going to be used by both Projects and Ideas

Example:

Project      Idea             Comments
------       -----------      --------------
PID          IID              comment_id
title        proyect_id       comment_parent
eg_url       eg_idea_title    **Project/idea ID** // This one is my problem

So I don't know whats the best approach to differentiate if a comment belongs to a Project or a Idea.

Im thinking on create another "Objects" table, to genere really unique objects_id for whatever other table (like Project or Idea) and use that object_id to reference the comments table (or any other table that needs to be share for two or more tables)..

Objects                        Comments            
------                         -----------
object_id                      comment_id         
obj_type (Project / Idea)      comment_parent    
Project/Idea ID                object_id    <-- Use the object ID
mysqlsql


Solution 1:[1]

You use a reference/lookup table to attribute the file to either project or idea:

file      fileProject    fileIdea
------    -----------    ----------
id        fileId         fileId
          projectId      ideaId

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Kermit

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