MongoDB dropIndexes()

In MongoDB, the dropIndexes() method allows you to drop one or more indexes from a collection.

To drop a single index, pass the name of the index or its definition/specification document. If it’s a text index, you can only specify the index name.

To drop multiple indexes, pass the index names in an array.

To drop all indexes (except for the _id index), don’t pass any arguments.

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How hideIndex() Works in MongoDB

MongoDB introduced the db.collection.hideIndex() method in MongoDB 4.4.

This method hides an existing index from the query planner. This allows you to evaluate the potential impact of dropping an index without actually dropping the index.

If hiding it has a negative impact, you can use db.collection.unhideIndex() to unhide the index. This saves you from having to drop the index, then recreate it.

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The Import Modes of mongoimport

When using mongoimport to import files into MongoDB, you have the option of specifying a mode to use. These modes determine what happens if there’s already matching documents in the collection that you’re trying to import into.

By default, mongoimport uses insert mode, but there are other modes you can use. The mode you use will depend on what you’re trying to do.

Below is an overview of each mode along with examples.

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MongoDB distinct()

In MongoDB, the db.collection.distinct() method finds the distinct values for a specified field across a single collection or view and returns the results in an array.

Distinct values are those with redundant duplicates removed. Distinct values are unique values. For example, if you have 2 or 3 documents with the same value, the distinct command will return just one value.

db.collection.distinct() is a shell wrapper method for the distinct command.

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MongoDB $sortByCount Aggregation Operator

In MongoDB the $sortByCount aggregation pipeline stage groups incoming documents based on the value of a specified expression, then computes the count of documents in each distinct group.

Each group is output in its own document, which consists of two fields:

  • an _id field containing the distinct grouping value, and
  • count field containing the number of documents belonging to that grouping.

The documents are sorted by count in descending order.

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