[fhunt]

> our data was an inconsistent

Because you didn't put strict validation before data entered Mongo and I guess you didn't use a typed lang which makes such a validation like a no-brainer and quite natural.

SQL gives you type checking for free, Mongo does not. However, if you have a typed lang and have a proper validation in place you just have to define those at one place and not in the database and in your app (DRY).