Migration / versions of data definitions

[Jorgen-P]

I can't find any documentation about or example of changing definitions for data and migrating old data to it. Would you create a new class and migrate the data in the application with no direct support from xodus-dnq? Would you have to move everything linked to new definitions as well?

[lehvolk]

We recommend to write application code for data migration.

Renaming entity type, property or link

You can use aliases for all properties, links, blobs and entity types. Like var email by xdStringProp(dbName="_email_") or object : XdNaturalEntityType("OldDeprecatedName")

Data structure migration

This is the most problematic case. When you run application with new model definition you should apply new model definition to the database. It's better to do as a separate startup step. Migration code will use only new model definition so cascade operations from old model definition should be applied manually.

We can give some recommendations:

• use batches for processing large datasets
• If dataset is very large then probably using low-level api (Store API) of the database can dramatically reduce execution time (keep in mind that constraints and cascade operations defined in DNQ will not be triggered). In YouTrack we use this when we need to update really huge set (>1M of records or more at the moment). Sometimes it gives x30 boost.

I will add this into our documentation somewhere.

[Jorgen-P]

Thank you for the advice.