Migration Guide 12.0 to 12.1 - LuckyPennySoftware/MediatR GitHub Wiki

With 12.1, AddMediatR no longer scans for any implementations of:

• Behaviors
• Stream behaviors
• Pre-processors
• Post-processors

You will need to explicitly register these with methods:

• Behaviors
  • AddBehavior
  • AddOpenBehavior
• Stream behaviors
  • AddStreamBehavior
  • AddOpenStreamBehavior
• Pre processors
  • AddRequestPreProcessor
  • AddOpenRequestPreProcessor
• Post processors
  • AddRequestPostProcessor
  • AddOpenRequestPostProcessor

Since you couldn't change the order of these with the scanning approach, AddMediatR now registers with ServiceCollection in the exact order added to each list of registrations.