MongoDB $ifNull

In MongoDB, $ifNull is an aggregation pipeline operator that allows you to specify a value to use in place of null.

The way that it works is, you provide an expression and a replacement expression. If the expression evaluates to a non-null value, that expression is returned. But if the expression evaluates to a null value, $ifNull returns the value of the replacement expression.

A null value includes instances of undefined values or missing fields.

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MongoDB $filter

In MongoDB, the $filter aggregation pipeline operator returns a subset of an array based on a specified condition.

The $filter operator returns an array with only those elements that match the condition, in their original order.

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MongoDB $exp

In MongoDB, the $exp aggregation pipeline operator raises Euler’s number (i.e. e ) to the specified exponent and returns the result.

The exponent can be any valid expression that resolves to a number.

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MongoDB $tanh

In MongoDB, the $tanh aggregation pipeline operator returns the hyperbolic tangent of a value that is measured in radians.

$tanh accepts any valid expression that resolves to a number.

The $tanh operator was introduced in MongoDB 4.2.

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MongoDB $cond

In MongoDB, the $cond aggregation pipeline operator evaluates a boolean expression, and returns one of the two specified return expressions, depending on whether the boolean expression is true or false.

The $cond operator accepts two syntaxes: a longhand syntax and a shorthand syntax. Examples of each are below.

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