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Comment by threeseed | Hacker News Reader

MongoDB absolutely stores numbers as numbers. Always has.

And yes in a schemaless database you are required to manage the schema in your application layer as opposed to within the database. If we wanted a database with a rigid schema we would just use a SQL database.

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He said can it guarantee that the field "length" will always be a number and not..eg a string, or a list, or an object.

Why would it guarantee that ? It's a schema less database. It's not supposed to do that.

And my point is that if you query a single document and the field is a number then it will be returned as a number i.e. it physically stores and understands numbers.

Elasticsearch is schemaless as well, however it can guarantee that a field is a number once used.

Elasticsearch is not schemaless. It typically requires you to define a mapping (schema) upfront. You can set it to automatically infer the mapping based on the available data but this does not make it truly schemaless.

MongoDB allows a free form schema for every document. You're again comparing apples and oranges.

Just to be clear, a better term would be "dynamic schema". You can ask for data type validation since 3.2.

Schemaless by definition means this is not guaranteed. The same property name can hold different types of data from one object to the next. Several other key-value/wide-column have the same exact setup.

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