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Multikey Indexes

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  • Overview
  • Sample Data
  • Create a Multikey Index
  • Collation

Multikey indexes are indexes that improve performance for queries that specify a field with an index that contains an array value. You can define a multikey index by using the same syntax as a single field or compound index.

The examples in this guide use the sample_mflix.movies collection from the Atlas sample datasets. To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with PyMongo.

The following example creates a multikey index on the cast field:

result = movies.create_index("cast")

The following is an example of a query that uses the index created in the preceding code example:

query = { "cast": "Viola Davis" }
cursor = movies.find(query)

Multikey indexes behave differently from other indexes in terms of query coverage, index bound computation, and sort behavior. To learn more about multikey indexes, including a discussion of their behavior and limitations, see the Multikey Indexes guide in the MongoDB Server manual.

When you create an index, you can specify a default collation for all operations you perform on fields that are included in the index.

A collation is a set of language-specific rules for string comparison, such as for letter case and accent marks.

To specify a collation, create an instance of the Collation class or a Python dictionary. For a list of options to pass to the Collation constructor or include as keys in the dictionary, see Collation in the MongoDB Server manual.

Tip

Import Collation

To create an instance of the Collation class, you must import it from pymongo.collation.

To use an index with a specified collation, your operation must meet the following criteria:

  • The operation uses the same collation as the one specified in the index.

  • The operation is covered by the index that contains the collation.

The following example creates the same index as the previous example, but with a default collation of fr_CA:

from pymongo.collation import Collation
result = movies.create_index("cast", collation=Collation(locale='fr_CA'))

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