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You can use Firestore in Datastore mode (Datastore) for storing data for your applications that run in the standard environment. Datastore uses indexes for every query your application makes. These indexes are updated whenever an entity changes, so the results can be returned quickly when the app makes a query. To do this, Datastore needs to know in advance which queries the application will make. You specify which indexes your app needs in a index.yaml configuration file. You can use the Datastore emulator to generate the file automatically as you test your app, or write the file yourself. The index.yaml file must be uploaded when you deploy your app.
index.yaml
Every Datastore query made by an application needs a corresponding index. Indexes for simple queries, such as queries over a single property, are created automatically. Indexes for complex queries must be defined in a configuration file named index.yaml. This file is uploaded with the application to create indexes in Datastore.
The following is an example of an index.yaml file:
indexes:
- kind: Cat
ancestor: no
properties:
- name: name
- name: age
direction: desc
- kind: Cat
properties:
- name: name
direction: asc
- name: whiskers
direction: desc
- kind: Store
ancestor: yes
properties:
- name: business
direction: asc
- name: owner
direction: asc
The syntax of index.yaml is the YAML format. For more information about this syntax, see the YAML website for more information.
#) character is ignored:# This is a comment. Index definitions
index.yaml has a single list element called indexes. Each element in the list represents an index for the application.
An index element can have the following elements:
kind
properties
A list of properties to include as columns of the index, in the order to be sorted: properties used in equality filters first, followed by the property used in inequality filters, then the sort orders and their directions.
Each element in this list has the following elements:
name
direction
asc for ascending or desc for descending. This is only required for properties used in sort orders of the query, and must match the direction used by the query. The default is asc.
ancestor
You can create an index file manually, using a text editor and following the file layout described above. A more efficient approach is to automatically generate the file as you test your app locally. You can combine the two methods.
When you are testing in your local environment, you can use the gcloud emulator command to start a service that emulates Datastore before you run your app:
gcloud beta emulators datastore start --data-dir DATA-DIR
Use the --data-dir flag to specify the directory where the auto-generated index.yaml file will appear.
As you test your app, each time you generate a Datastore query, the emulator adds a generated index definition to index.yaml. All the automatically generated index definitions will appear in the file below the following line:
# AUTOGENERATED
All index definitions above this line are considered to be under manual control, and are not updated by the development web server. The web server will only make changes below the line, and will only do so if the complete index.yaml file does not describe an index that accounts for a query executed by the application. To take control of an automatic index definition, move it above this line.
The emulator may update existing definitions below this line as the application makes queries. If the app generates every query it will make while you test it, then the generated entries in index.yaml will be complete. You might need to edit the file manually to delete indexes that are not used in production, or to define indexes that were not created while testing.
To deploy the index.yaml configuration file, run the following command:
gcloud app deploy index.yaml
When you change or remove an index from the index configuration, the original index is not deleted from App Engine automatically. This gives you the opportunity to leave an older version of the app running while new indexes are being built, or to revert to the older version immediately if a problem is discovered with a newer version.
When you are sure that old indexes are no longer needed, you can delete them from App Engine as follows:
gcloud datastore indexes cleanup index.yaml
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-07 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-07 UTC."],[[["Datastore utilizes indexes for every query, which are defined in an `index.yaml` configuration file, ensuring quick query results."],["Simple query indexes are created automatically, while complex query indexes must be manually specified in the `index.yaml` file."],["The `index.yaml` file can be automatically generated using the Datastore emulator during local testing, and this file needs to be uploaded with the application."],["The `index.yaml` uses YAML format, featuring a list called `indexes` where each item defines an index with elements such as `kind`, `properties`, and `ancestor`."],["Unused indexes are not automatically removed from App Engine, and can be deleted later with the `gcloud datastore indexes cleanup index.yaml` command, allowing time for new index creation and easy reversion."]]],[]]
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