String Injection

Provider resolution by name

The @inject decorator can be used to inject a provider by its name. This is useful when you want to inject a provider that is not directly imported in the current module.

This serves two primary purposes:

• A higher level of decoupling between container and your code.
• Avoiding circular imports.

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Usage

To inject a provider by name, use the Provide marker with a string argument that has the following format:

Container.Provider[.attribute.attribute...]

The string will be validated when it is passed to Provide[], thus will raise an exception immediately.

For example:

from that_depends import BaseContainer, inject, Provide

class Config(BaseSettings):
    name: str = "Damian"

class A(BaseContainer):
    b = providers.Factory(Config)

@inject
def read(val = Provide["A.b.name"]):
    return val

assert read() == "Damian"

Container alias

Containers support aliases:

class A(BaseContainer):
    alias = "C" # replaces the container name.
    b = providers.Factory(Config)

@inject
def read(val = Provide["C.b.name"]): # `A` can no longer be used.
    return val

assert read() == "Damian"

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Considerations

This feature is primarily intended as a fallback when other options are not optimal or simply not available, thus is recommended to be used sparingly.

If you do decide to use injection by name, consider the following:

• In order for this type of injection to work, your container must be in scope when the injected function is called:

  from that_depends import BaseContainer, inject, Provide
  
  @inject
  def injected(f = Provide["MyContainer.my_provider"]): ...
  
  injected() # will raise an Exception
  
  class MyContainer(BaseContainer):
      my_provider = providers.Factory(some_creator)
  
  injected() # will resolve
  

• Validation of whether you have provided a correct container name and provider name will only happen when the function is called.