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The $expr operator allows the use of aggregation expressions within the query language. This enables more complex queries by allowing field comparisons, arithmetic operations, and other expressions directly within the query. Use cases for $expr include filtering documents based on computed values, comparing fields within the same document, and performing operations that would otherwise require a separate aggregation pipeline.
The basic syntax for using the $expr operator is as follows:
{
$expr: { <expression> }
}
| Description | |
|---|---|
expression |
An aggregation expression that evaluates to a boolean. The expression can include field paths, arithmetic operations, logical operations, and more. |
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