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I have 3 content types (blogs, photos, videos) that all reference the same "topic" vocabulary.

When I add the term reference field to each content type I can either create a new field "field_blog_topic", "field_photo_topic" and "field_video_topic" for each of the types.

Or I could create a "field_topic" field for blogs and then use that existing field for the photo and video content types.

Would it make any practical difference?

  • If you dig, there is a very similar question with some good answers having to do with the performance impacts. I cannot find it, though. – mpdonadio Feb 15 '12 at 22:10
  • yeah, that would be interesting, please post if you find it – uwe Feb 15 '12 at 23:49
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  • thanks a bunch. The 2 extra tables won't make a real difference in my case. – uwe Feb 16 '12 at 1:17
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Yes it would make sense to have only one field that you attach to multiple content types.

If you're using a MySQL backend then a table is created for every field you create in the UI (it's probably similar for other storage backends). If you create a single field and attach it to several different entity/bundle types then only a single table is created with the values for all entities. Fewer tables is definitely more desirable.

Also if you wanted to query the database for all nodes that are within a certain vocabulary (using EntityFieldQuery or even Views) then the query generated would have two less JOINs to make which is just much better for performance on the whole.

I think it was the intention of the developers that fields be used in this way, there's a complicated mechanism in place for managing different instances of fields and I don't think that logic would need to exist if they weren't supposed to be used like this.

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I don't know if it's better or not, but I like to have 1 vocabulary per content type. That way, I can create 3 different term reference fields. I find it more logical, especially when it comes to creating taxonomy menus and using terms in views for each of my content types.

However, I don't know the effects on performance.

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