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Considerations for Multi-Client Applications

Often when dealing with applications/systems that serve multiple clients, we encounter a situation where

  • Clients share some core functionality and algorithms
  • Clients have custom logic that extends the core functionality
  • Clients have customized data structures that extend core data structures
The key to making this work in a maintainable way (that is, without infusing the code with crazy branching statements or writing the whole application in dynamic SQL) is maintaining a distinct separation between core and client.

Here I present components from a simple, hypothetical application that demonstrates such a separation. The application is meant to evaluate whether or not a client should acquire a player for fantasy football. It contains some core functionality for doing the evaluation (it doesn't pick up a player who has never scored a point) and a core data structure that represents a player. There are two clients who extend this core functionality: me and a stupid opponent in my league. The stupid opponent is a Bears fan who only picks up Bears players. I am a player who uses some trivial evaluation strategy and also extends the core data structure with some data that represents my own opinion.

The code shows an example of how to define and extend core functionality. It does not show how to wire everything together (dependency injection) or how to persist custom data. I may explore these topics in future posts. Also note that I called the code repository 'MultiTenancy', but this is more likely something you'll find in multi-instance scenario. I'm using the term 'multi-client' to represent both possibilities.

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