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+Migration to 0.4.0
+---
+
+[Migration to 0.4.0 Tool](https://github.com/hackmdio/migration-to-0.4.0)
+
+We've dropped MongoDB after version 0.4.0.
+So here is the migration tool for you to transfer the old DB data to the new DB.  
+This tool is also used for official service.
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