According to https://docs.mongodb.com/manual/reference/bson-type-comparison-order/#objects, embedded objects/documents are compared, first, by field names, second, by field values.

Consider a collection:

{_id: 1, tag: {bab: 123}}
{_id: 2, tag: {bar: "BAR"}}
{_id: 3, tag: {baz: "BAZ"}}

and a query:

{tag: {$gte: {baz: MinKey()}}}

I thought this would return ONLY doc 3 (since `bab` and `bar` are less than `baz`), but it returns ALL three docs. Changing the query to

{tag: {$gte: {baz: ""}}}

 
returns ONLY doc 3, as I hoped.

Is this an issue? Are range queries supported on whole embedded objects values? Do MinKey and MaxKey have some weird behavior in queries embedded documents?