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MongoDB, Grails and Relationships

I was wondering how the MongoDB plugin for Grails will handle relationships. To test this, I made a very simple application with two domain classes:

Authorhave two fields: String firstNameandString lastName

Bookhave two fields: String titleandAuthor author

After you configure MongoDB Grails and I made a few Authorand Bookand looked into the MongoDB interactive shell. I found that relations are processed in the same way as they will be processed in a relational database: links to id fields of other objects.

So now for the questions:

  • For GORM to pull this out, does a separate connection is required to retrieve each document?
  • If so, is this not better in a relational database like PostgreSQL or MySQL?
  • If the answer to the above two questions is really yes, then is there a better way to manage relationships in a document database such as MongoDB? I understand that MongoDB should not be relational, but there are some things that I don’t see how to get around relationships without duplicating data (thereby doing nightmares updates).

Edit: I also noticed that grails is not sorting correctly by id property for my authors. Is this related to using MongoDB? In the shell, I see that the _id property of all documents made by Grails is data type NumberLong.

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