
Where Do I Put My Business Rules and Validation? - jamesmh
https://builtwithdot.net/blog/where-do-i-put-my-business-rules-and-validation
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smush
Short version: Use Domain Driven Design. Business Rules / Validation go into
the Value Objects (a name, an address, etc.) that make up an entity (a unique
customer, business account, etc.). The article defines each term in the
previous sentence and gives a sample as to how to perform it.

For a Functional Programming perspective or if you are a F# user, the
Pragmatic Bookshelf book "Domain Modeling Made Functional" covers DDD
architecture from a functional perspective and was an informative read.

