4 Replies Latest reply on Apr 21, 2009 12:16 PM by comment_1

    relation graph relational database

    willem67

      Title

      relation graph relational database

      Post

      I use a many-to-many relation with a join table. It works well in my new databases.

       

      Now I want to apply this technique to an database that I contructed a bit earlier. I found something strange in my relation graph:

       

      In my new database the relation between the tables appears like a line with three little fingers (do not know how to call it...) on the side of the join table. In my other database it appears like a straight line without fingers; and my relations do not function well. Currently I believe that the lack of these finger is the problem.

       

      Question: How do you make the three fingers appear where you want? (I did not choose anything particular for the database that does work very well; it just happened automatically). I did some tests and everytime the fingers ended up on the join table. But not with one particular database.

       

      Willem

        • 1. Re: relation graph relational database
          comment_1
            

          These "fingers" (commonly called 'crow's feet') indicate that there can be many related records on this side of the relationship. In a standard join table implementation, the graph would look something like:

           

          Projects -< Tasks >- People

           

          which can be read as "a project has many tasks, and each task is assigned to a single person".

           

           

          However, the way the relationships graph is drawn is only an indication of how the relationships were defined - so it is hard to tell what went wrong without more details.

          • 2. Re: relation graph relational database
            Jade
              

             


            willem67 wrote:

            … In my other database it appears like a straight line without fingers; and my relations do not function well.


             

             

             

            Just to add a detail to what Comment has said, a straight line without crows feet indicates that the match field is intended to match a single record, such as an auto-entered value.  If it is a straight line with a vertical bar, that indicates that the match field is intended to match a global field.


            • 3. Re: relation graph relational database
              willem67
                

              Thank you. It is still a mystery how a database and/or the relationship graph determines where to put the crow's feet.

               

              However, since I have changed the fieldname from exampleID into IDexample it puts the crow's feet back in the graph.

               

              Is this a coincidence or is this right indeed?

               

              Willem

               

               

              • 4. Re: relation graph relational database
                comment_1
                  

                willem67 wrote:

                It is still a mystery how a database and/or the relationship graph determines where to put the crow's feet. 


                It's not a mystery at all. If the matchfield is defined to be unique (e.g. by validation, or by auto-entering a serial number), there will no crow's feet on that side.

                 


                willem67 wrote:

                I have changed the fieldname from exampleID into IDexample it puts the crow's feet back in the graph.

                 

                Is this a coincidence or is this right indeed?


                A field's name has no bearing on the issue.