###Dependency Injection for Go
Digo is inspired in the way that the Spring framework for Java allows dependency injection using an configuration file. The difference is that digo uses Json instead of XML and, for language limitations, the Types must be registered.
There are also other DI libraries that work without using reflection, Octopus is a good example.
##Install
Download the repository with:
go get github.com/cone/digo
Then include the project inside your project like this:
import "github.com/cone/digo"
##What it does
Digo allows dependency injection using a configuration file.
Lets suppose we have ProductController struct as follows:
type ProductController struct{
DB Repository
Validator DataValidator
}
ProductController has 2 dependencies: DB of type Repository and Validator of type DataValidator, we want to follow the inversion of controll principle so both are interfaces:
type Repository interface{
Get(int) interface{}
}
type DataValidator interface{
Validate(interface{}) bool
}
Also we have custom implementations of each of those interfaces for products, for example, we have these for the Repository interface:
type ProductRepo struct{}
func (this *ProductRepo) Get(id int) interface{}{
//...reads from db...
return product
}
type TestProductRepo struct{}
func (this TestProductRepo) Get(id int) interface{}{
return Product{id, "Test Product"}
}
First we have to add the types to the TypeRegister like this:
TypeRegistry.Add(ProductController{})
TypeRegistry.Add(ProductRepo{})
TypeRegistry.Add(ProductValidator{})
Then we should write a configuration file like this called prod.json:
{
nodes: {
"product_repo": {
"type": "myPackage.ProductRepo",
"is_pointer": true,
},
"product_validator": {
"type": "myPackage.ProductValidator",
}
"product_ctrl": {
"type": "myPackage.ProductController",
"deps": [
{
"id": "product_repo",
"field": "DB"
},
{
"id": "product_validator",
"field": "Validator"
}
]
}
}
}
In the file we define the types and their dependencies. We use an alias to name the type e.g. product_repo for myPackage.ProductRepo then we specify the type and if the dependency is a pointer we set the is_pointer field to true, note that this is true for myPackage.ProductRepo because only a pointer to it satisfies the Repository interface.
Now we can create a Context with that file. The Context allow us to easily change the dependencies whe are injecting, that is useful if when testing: suppose we have a test.json file, in that file, instead of myPackage.ProductRepo we specify myPackage.TestProductRepo which is a test double. having those two files we can create a production context and a test context.
prodCtx, err := ContextFor("prod.json")
//...error handling...
testCtx, err := ContextFor("test.json")
//...error handling...
Finally the context is able to generate our ProductController using the alias we specified in the json file:
pi, err := prodCtx.Get("product_repo")
//...error handling...
productController := pi.(ProductController)
ti, err := testCtx.Get("product_repo")
//...error handling...
testProductController := ti.(ProductController)
The gererated ProductController will already have its dependencies ProductRepo and ProductValidator ready for use!
product := productController.DB.Get(1)
##Usage
###ContextFor
It returns a Context element from a given config file.
ctx, _ := ContextFor("prod.json")
###TypeRegistry
Its pourpose is to register the types of the elements that are going to be injected or created.
####Add
It allows to add a type. You must not pass a pointer to it, that is must be specified in the config file with the is_pointer flag.
TypeRegistry.Add(ProductController{})
####AddType
It allows to add a type passing directly a reflect.Type element.
TypeRegistry.AddType(reflect.TypeOf(PorductController{}))
####Get
It allows to get a reflect.Type element passing a string containing the name of the type.
t, _ := TypeRegistry.Get("myPackage.Foo")
###Context
It holds a given configuration that will be use to determine what dependencies will be injected to an element
####Get
It will return the given type's interface by its alias.
i, _ := cxt.Get("foo")
foo := i.(Foo)
##Configuration file
The configuration file holds a Json string describing the components and their dependencies.
###Component fields
####Type
It describes the type of the component including the package.
...
"type": "myPackage.Foo",
...
####Is_pointer
A flag to specify that the component is a pointer (false by default). If it is not a "singleton", digo will create a new instance and return a pointer to it.
....
"is_pointer": true,
....
####Scope
It descibes the scope of the component. This field can hold two values: prototype and singleton.
If 'prototype' is used, a copy of the component will be created each time Context.Get is called. This is the default behavior is no 'scope' is specified.
...
"scope": "prototype"
...
If 'singleton' is used, a reference to the same component will be returned each time Context.Get is called. The variable or struct field that will hold the singleton should be a pointer.
...
"scope": "singleton"
...
####Deps
It descibes the dependencies of the component. Here the id of the component used as a dependency should be specified and the name of the field that will hold it e.g.
...
"foo":{
"type": "myPackage.Foo"
},
"deps":[
{
"id": "foo",
"field": "MyFoo"
}
]
...
##Initializer Interface
If one of the dependencies implements the Initializer interface, th BeforeInject function will be called before the dependency is injected. This could be useful to initialize the values of the dependency e.g.
type Bar struct{
db DB
}
func (this *Bar) GetDBConnection() DB{
return this.db
}
func (this *Bar) BeforeInject() error{
return this.db.Open()
}
- Create your feature branch (
git checkout -b feature/my-new-feature) - Commit your changes (
git commit -am 'Add some feature') - Push to the branch (
git push origin feature/my-new-feature) - Create a new Pull Request