41 lines
2.8 KiB
Markdown
41 lines
2.8 KiB
Markdown
# Custom transformers
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When the capabilities of the generic `contractWatcher` are not sufficient, custom transformers tailored to a specific
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purpose can be leveraged.
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Individual transformers can be composed together from any number of external repositories and executed as a single process using
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the `compose` and `execute` commands or the `composeAndExecute` command.
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## Writing custom transformers
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For help with writing different types of custom transformers for the `composeAndExecute` set of commands, please see the below:
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Storage Transformers
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* [Guide](../../staging/libraries/shared/factories/storage/README.md)
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* [Example](../../staging/libraries/shared/factories/storage/EXAMPLE.md)
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Event Transformers
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* [Guide](../../staging/libraries/shared/factories/event/README.md)
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* [Example 1](https://github.com/vulcanize/ens_transformers/tree/master/transformers/registar)
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* [Example 2](https://github.com/vulcanize/ens_transformers/tree/master/transformers/registry)
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* [Example 3](https://github.com/vulcanize/ens_transformers/tree/master/transformers/resolver)
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Contract Transformers
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* [Example 1](https://github.com/vulcanize/account_transformers)
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* [Example 2](https://github.com/vulcanize/ens_transformers/tree/master/transformers/domain_records)
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## Preparing custom transformers to work as part of a plugin
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To plug in an external transformer we need to:
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1. Create a package that exports a variable `TransformerInitializer`, `StorageTransformerInitializer`, or `ContractTransformerInitializer` that are of type [TransformerInitializer](../staging/libraries/shared/transformer/event_transformer.go#L33)
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or [StorageTransformerInitializer](../../staging/libraries/shared/transformer/storage_transformer.go#L31),
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or [ContractTransformerInitializer](../../staging/libraries/shared/transformer/contract_transformer.go#L31), respectively
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2. Design the transformers to work in the context of their [event](../staging/libraries/shared/watcher/event_watcher.go#L83),
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[storage](../../staging/libraries/shared/watcher/storage_watcher.go#L53),
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or [contract](../../staging/libraries/shared/watcher/contract_watcher.go#L68) watcher execution modes
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3. Create db migrations to run against vulcanizeDB so that we can store the transformer output
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* Do not `goose fix` the transformer migrations, this is to ensure they are always ran after the core vulcanizedb migrations which are kept in their fixed form
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* Specify migration locations for each transformer in the config with the `exporter.transformer.migrations` fields
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* If the base vDB migrations occupy this path as well, they need to be in their `goose fix`ed form
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as they are [here](../../staging/db/migrations)
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To update a plugin repository with changes to the core vulcanizedb repository, run `dep ensure` to update its dependencies.
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