## Plugins

This directory is for Exporter plugins (.go and .so files) generated by, output from, and linked to from the composeAndExecute command  
These plugins are generated using information provided in a .toml config file 

The config file requires, at a minimum, the below fields:

```toml 
[database]
    name = "vulcanize_public"
    hostname = "localhost"
    user = "vulcanize"
    password = "vulcanize"
    port = 5432

[client]
    ipcPath = "http://kovan0.vulcanize.io:8545"

[exporter]
    filePath = "$GOPATH/src/github.com/vulcanize/vulcanizedb/plugins/"
    fileName = "exporter"
    [exporter.transformers]
            transformer1 = "github.com/path/to/transformer1"
            transformer2 = "github.com/path/to/transformer2"
            transformer3 = "github.com/path/to/transformer3"
```

In the above, the exporter.transformers are mappings of import aliases to their import paths 
If the individual transformers require additional configuration variables be sure to include them in the .toml file 

The general structure of a plugin .go file, and what we would see with the above config is below   
Note that `shared_transformer` is a reserved alias needed for the generic TransformerInitializer type:

```go
package main

import (
	shared_transformer "github.com/vulcanize/vulcanizedb/libraries/shared/transformer"
	transformer1 "github.com/path/to/transformer1"
	transformer2 "github.com/path/to/transformer2"
	transformer3 "github.com/path/to/transformer3"
)

type exporter string

var Exporter exporter

func (e exporter) Export() []shared_transformer.TransformerInitializer {
	return []shared_transformer.TransformerInitializer{
		transformer1.TransformerInitializer,
		transformer2.TransformerInitializer,
		transformer3.TransformerInitializer,
	}
}
```

As such, to plug in an external transformer all we need to do is create a [package](https://github.com/vulcanize/maker-vulcanizedb/blob/compose_and_execute/pkg/autogen/test_helpers/bite/initializer.go) that exports a variable `TransformerInitializer` that is of type [TransformerInitializer](https://github.com/vulcanize/maker-vulcanizedb/blob/compose_and_execute/libraries/shared/transformer/transformer.go#L19)   
As long as the imported transformers abide by the required interfaces, we can execute over any arbitrary set of them