将 mongoDB 集合转换为 mySQL 数据库

Question

I was created my project in spring 4 MVC + Hibernate with MongoDB. now, I have to convert it into the Hibernate with MySQL. my problem is I have too many collections in MongoDB the format of bson and json. how can I convert that file into MySQL table format? is that possible?

Answer 1

The documents in your MongoDB collections represent serialised forms of some classes (POJOs, domain object etc) in your project. Presumably, you read this data from MongoDB deserialise it into its class form and use it in your project eg display it to end users, use it in calculations, generate reports from it etc.

Now, you'd prefer to host that data in MySQL so you'd like to know how to migrate the data from MongoDB to MySQL but since the persistent formats are radically different you are wondering how to do that.

Here are two options:

• Use your application code to read the data from MongoDB, deserialise it into your classes and then write that data into MySQL using JDBC or an ORM mapping layer etc.
• Use mongoexport to export the data from MongoDB (in JSON format) and then write some kind of adapter which is capable of mapping this data into the desired format for your MySQL data model.

The non functionals (especially for the read and write aspects) will differ between these approaches but fundamentally both approaches are quite similar; they both (1) read from MongoDB; (2) map the document data to the relational model; (3) write the mapped data into MySQL. The trickiest aspect of this flow is no. 2 and since only you understand your data and your relational model there is no tool which can magically do this for you. How would a thirdparty tool be sufficiently aware of your document model and your relational model to be able to perform this transformation for you?

You could investigate a MongoDB JDBC driver or use something like Apache Drill to facilitate JDBC queries onto your Mongo DB. Since these could return java.sql.ResultSet you would be dealing with a result format which is more suited for writing to MySQL but it's likely that this still wouldn't match your target relational model and hence you'd still need some form of transformation code.

Answer 2

Mongodb is a non-relational database, while MySQL is relational. The key difference is that the non relational database contains documents (JSON objects) which can contain hierarchical structure, where as the relational database expects the objects to be normalised, and broken down into tables. It is therefore not possible to simply convert the bson data from MongoDB into something which MySQL will understand. You will need to write some code that will read the data from MongoDB and the write it into MySQL.