Function Validate

Attach validation rules — to one field, or to the whole model.

On a property the rules are per-column, and run before every insert and update:

`@Validate`({ isEmail: true, len: [5, 254] })
declare email: string;

`@Validate`({ isIn: [['draft', 'live']], msg: 'unknown status' })
declare status: string;
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On the class the values are functions, called with this bound to the instance — the place for a rule that spans columns, which no per-column rule can express. A validator reports by throwing:

`@Validate`({
  endsAfterStart() {
    if (this.endsAt <= this.startsAt) throw new Error('endsAt must be after startsAt');
  },
})
class Event extends Model {}
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Applying it twice merges, so rules can be split across lines or inherited from a base class.