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Comment by shortrounddev2 | Hacker News Reader

In linq (C#)

    IEnumerable<User> getExpiredUsers(DbSet<User> users)
        => users.Where(u => u.ExpiresAt < DateTime.UtcNow);

Such simple logical expressions (called expression trees) get converted to SQL queries

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The is exactly the way forward: encapsulation (the function), type safety, and dynamic/lazy query construction.

I'm building a new project, Typegres, on this same philosophy for the modern web stack (TypeScript/PostgreSQL).

We can take your example a step further and blur the lines between database columns and computed business logic, building the "functional core" right in the model:

  // This method compiles directly to a SQL expression
  class User extends db.User {
    isExpired() {
    return this.expiresAt.lt(now());
    }
  }

  const expired = await User.where((u) => u.isExpired());

Here's the playground if that looks interesting: https://typegres.com/play/

And anyone who calls that method may find themselves dealing with the implementation details of Entity Framework and whatever db provider you're using because it's a leaky abstraction.

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