A Beginners' Guide to Blazor WebAssembly - Data validation and preventing duplicates

Data validation in a Blazor WebAssembly application using Data Annotations, plus how to prevent duplicate records getting added to the database.
Useful links:
Video script & code: blazorcode.uk/countriesandcit...
Data Annotations examples: www.codemag.com/Article/23010...
A Practical Guide to Dapper: www.red-gate.com/simple-talk/...
StackOverflow - Carriage return behaviour: stackoverflow.com/questions/6...

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