Query Operators: $gt, $in, $regex, $exists, $elemMatch

The CRUD chapter used find() with simple equality filters: matching a category or matching an ID. Real application features need more expressive filters. A price-range filter, an any-of-these-categories search, a check for products missing a field, and a query against items inside an order are not simple equality checks. MongoDB expresses these cases with query operators: special keys that begin with $ and describe how MongoDB should match a field or condition. This lesson covers the operator families you will use most often.

Note: The examples are runnable mongo shell queries against the seeded ecommerce collections. Each demonstrates one operator family on realistic data.

To make the operators concrete, the next visual should group them by the kind of condition they express:

That grouping starts with comparison.

Comparison operators

Comparison operators match a field against a value by something other than exact equality, which is what makes range queries possible.

• $gt, $gte ...