In MongoDB, the $allElementsTrue aggregation pipeline operator evaluates an array as a set and returns true if no element in the array is false.
If the array contains an element that is false, then $allElementsTrue returns false.
An array’s element is true if it’s not false, null, 0, or undefined.
If you’ve used T-SQL you will probably be familiar with the GO command. This command is often placed at the end of a batch of statements.
MongoDB has a $push operator and an $addToSet operator, both of which do a very similar thing.
Both operators append values to an existing array. The main difference is in how they deal with arrays that already contain the value you’re trying to append, and also in the modifiers that can be used.
Continue readingIn MongoDB, the $toUpper aggregation pipeline operator converts a string to uppercase and returns the result.
In MongoDB, the $toLower aggregation pipeline operator converts a string to lowercase and returns the result.
In MongoDB, you can use the $exists element query operator to match documents that contain a specific field.
You can also use it to match documents that don’t contain a specific field.
You can also use it in conjunction with other operators such $nin to match documents where a given field exists, but it doesn’t contain a specific value.
In MongoDB, the cursor.forEach() method iterates the cursor to apply a JavaScript function to each document from the cursor.
In MongoDB, the cursor.map() method applies a function to each document visited by the cursor and combines the return values in an array.
From MongoDB 4.4, you can use the $isNumber aggregation pipeline operator to check whether or not a value is a number.
It accepts any valid expression, and returns true if the expression is a number, false if it’s not.
The $replaceAll aggregation pipeline operator was introduced in MongoDB 4.4.
This operator replaces all instances of a search string in an input string with a replacement string and returns the result.
If the search string isn’t found, then $replaceAll returns the input string.