Dependency Injection

Definition

Dependency Injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies.

Source: Wikipedia

Example

Model

Code

csharp


internal class CancelMeetingCommandHandler : ICommandHandler<CancelMeetingCommand>
{
    private readonly IMeetingRepository _meetingRepository;
    private readonly IMemberContext _memberContext;

    internal CancelMeetingCommandHandler(IMeetingRepository meetingRepository, IMemberContext memberContext)
    {
        _meetingRepository = meetingRepository;
        _memberContext = memberContext;
    }

    public async Task<Unit> Handle(CancelMeetingCommand request, CancellationToken cancellationToken)
    {
        var meeting = await _meetingRepository.GetByIdAsync(new MeetingId(request.MeetingId));

        meeting.Cancel(_memberContext.MemberId);

        return Unit.Value;
    }
}

Description

A CancelMeetingCommandHandler needs two collaborators (dependencies) to fulfill its job - repository of meetings (IMeetingRepository) and information about member context (IMemberContext). It doesn't instance implementation of these interfaces itself - they are provided (injected) via construction (Constructor Injection).