How To Write Dynamic Migrations - Mohit Aghera

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How to write dynamic migration
Mohit Aghera, Mitesh Patel

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About Us
Mohit Aghera
- Back-end developer @Axelerant
- Drupal.org: mohit_aghera
- Twitter: @mohit_rocks
Mitesh Patel
- Back-end developer @Axelerant
- Known as @miteshmap over internet.

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Dynamic Migrations
● What are dynamic migrations ?
● Why do we need ?

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Migrations : Recap

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Migrations: A brief introduction
What Migrate API Provides:
● Migrate Data from source to destination
● Keeps track of record of migrated data
● Provides framework for writing migrations

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Migration Plugins
● Source Plugins
● Process Plugins
● Destination Plugins

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Migration Flow

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Understanding Derivatives
● Drupal 7 has “_info()” hooks
● Wonder how do we generate multiple blocks with single block plugin ?
● Drupal 8 has “Derivatives”
● Allows to generate instances dynamically

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How Derivatives works ?
● Plugin manager uses “Discovery” mechanism
● “DerivativeDiscoveryDecorator” decorator class

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Define along with Plugin

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Deriver Implementation
SystemMenuBlock Deriver implementation:

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Understanding Derivers
Notable Examples:
● SystemMenuBlock
● BlockContentBlock
● LanguageBlock
And many more..

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Possible approaches for migration
● Migration templates
● Config Entities

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Migration as Configuration entities
● Similar to any configurations
● Resides in [module]/config directory
● Typically names are given like “migrate.migration.node_page.yml”

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Migration as Configuration entities
Advantages:
● Easy to write and run
● No need to write specific logic to run unlike migration templates
Disadvantages:
● Not much flexible
● Hard to change runtime
● Dynamic migration generation is not possible
● Can’t generate based on user inputs

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Migration as templates
● Resides in [module]/migration_templates directory
● Names could match the migration id
● Typically names are given like “node_page.yml”

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Migration as templates
Advantages:
● Much more flexible than configuration entities for each variation
● Easy to change runtime
● Ability to generate dynamic migration using reusable templates

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Derivers for
Migration
● Works as a derivative for
new migrations
● Helps to create migrations
dynamically
● Extends DeriverBase class.

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Writing
Derivers
● Implement
getDerivativeDefinitions()
and write your logic.

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Using Derivers
Specify in migration template file.

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Running migration

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Use cases
● Migrating large amount of sites with similar architecture
but different languages in each site (our use case,
https://github.com/miteshmap/drupal_migration_demo)
● Core: Migrating D7 to D8
● Core: Migrating Workbench Moderation to Content
Moderation (https://www.drupal.org/project/wbm2cm)
● Migrating sites from Magento for instance with different
attributes for each site
● And many more...

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Thank you … for being here and allowing
us to contribute and share our knowledge
To summarise…
● We discussed how to make migrations more dynamic and
less painful
● We saw an example of how to write derivers
● We saw advantages of doing it, it is done in Core and many
contrib modules already

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References
Migration API : https://www.drupal.org/docs/8/api/migrate-api/migrate-api-overview
Reference module : https://github.com/mohit-rocks/drupalcamp-goa