As of mongoimport version 100.0.0, you can delete documents in MongoDB based on an imported file. To do this, use delete mode.
When you use delete mode, if an imported document has the same _id value as an existing one in the collection that you’re importing into, the existing document will be deleted.
You can also specify another field or fields (other than the _id field) to be the matching field if required.
In MongoDB, the $split aggregation pipeline operator divides a string into an array of substrings based on a delimiter.
The delimiter is removed from the string, and the substrings are added as elements to the array.
To use $split, you specify the string and the delimiter.
If the delimiter isn’t found in the string, the original string is returned as the only item in the array.
Continue readingIn MongoDB, the $slice aggregation pipeline operator returns a subset of an array.
To use $slice, you specify the number of elements to return from the array. You can also specify a starting position for which to take the subset from the array.
When you run queries In MongoDB, you have the option of limiting the documents returned. This is where you specify a maximum number of documents to be returned by the operation.
For example, if an operation would normally return 2,000 documents, but you specify a limit of 1,000, then only 1,000 documents are returned. However, if the operation would only return say, 500 documents, then all 500 are returned (because they don’t breach the 1,000 document limit).
This is a bit like using the TOP clause in SQL Server, or the LIMIT clause in MySQL, MariaDB, PostgreSQL, and SQLite.
In MongoDB, the $size aggregation pipeline operator counts and returns the total number of items in an array.
The $size operator accepts one argument. The argument can be any valid expression that resolves to an array.
In MongoDB, if you need to delete a document in the mongo shell, you can use:
db.collection.remove() methoddelete commanddb.collection.deleteOne() methoddb.collection.deleteMany() methodThis article provides examples of each.
Continue readingIn MongoDB, the $setUnion aggregation pipeline operator accepts two or more arrays and returns an array containing the elements that appear in any of those input arrays.
$setUnion accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setUnion treats the arrays as sets.
In MongoDB, the $setIsSubset aggregation pipeline operator accepts two arrays and returns true when the first array is a subset of the second, and false when it isn’t.
The first array is also considered a subset when it equals the second array.
Continue readingIn MongoDB, the $setIntersection aggregation pipeline operator accepts two or more arrays and returns an array that contains the elements that appear in all input arrays.
$setIntersection accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setIntersection treats the arrays as sets.
In MongoDB, the $setEquals aggregation pipeline operator compares two or more arrays and returns true if they have the same distinct elements and false otherwise.
$setEquals accepts two or more arguments, all of which can be any valid expression as long as they each resolve to an array. $setEquals treats the arrays as sets.