From MongoDB to PostgreSQL - Django

Question

Could any one shed some light on how to migrate my MongoDB to PostgreSQL? What tools do I need, what about handling primary keys and foreign key relationships, etc?

I had MongoDB set up with Django, but would like to convert it back to PostgreSQL.

Answer 1

Whether the migration is easy or hard depends on a very large number of things including how many different versions of data structures you have to accommodate. In general you will find it a lot easier if you approach this in stages:

1. Ensure that all the Mongo data is consistent in structure with your RDBMS model and that the data structure versions are all the same.

2. Move your data. Expect that problems will be found and you will have to go back to step 1.

The primary problems you can expect are data validation problems because you are moving from a less structured data platform to a more structured one.

Depending on what you are doing regarding MapReduce you may have some work there as well.

Answer 2

In the mean time, Postgres Foreign Data Wrapper for MongoDB has emerged (versions 9.1-9.4). With it, one can set up a view to MongoDB, via the PostgreSQL, and then handle the data as SQL.

This would probably mean rather easy way to copy data as well.

Limitations of FDW that I have faced:

• objects within arrays (in MongoDB) do not seem to be addressable
• objects with dynamic key names do not seem to be addressable

I know it's 2015 now. :)