How to configure an Expectation store on a filesystem

By default, newly profiled Expectations are stored in JSON format in the expectations/ subdirectory of your great_expectations folder. This guide will help you configure a new storage location for Expectations on your filesystem.

Prerequisites: This how-to guide assumes that you have already:

  • Configured a Data Context.

  • Configured an Expectation Suite.

  • Determined a new storage location where you would like to store Expectations. This can either be a local path, or a path to a network filesystem.

Steps

  1. Configure a new folder on your filesystem where Expectations will be stored.

    Create a new folder where you would like to store your Expectations, and move your existing Expectation files over to the new location. In our case, the name of the Expectations file is npi_expectations and the path to our new storage location is /shared_expectations.

    # in the great_expectations/ folder
    mkdir shared_expectations
    mv expectations/npi_expectations.json shared_expectations/
    
  2. Identify your Data Context Expectations Store

    In your great_expectations.yml , look for the following lines. The configuration tells Great Expectations to look for Expectations in a store called expectations_store. The base_directory for expectations_store is set to expectations/ by default.

    expectations_store_name: expectations_store
    
    stores:
        expectations_store:
            class_name: ExpectationsStore
            store_backend:
                class_name: TupleFilesystemStoreBackend
                base_directory: expectations/
    
  3. Update your configuration file to include a new store for Expectations results on your filesystem

    In the example below, Expectations Store is being set to shared_expectations_filesystem_store with the base_directory set to shared_expectations/.

    expectations_store_name: shared_expectations_filesystem_store
    
    stores:
        shared_expectations_filesystem_store:
            class_name: ExpectationsStore
            store_backend:
                class_name: TupleFilesystemStoreBackend
                base_directory: shared_expectations/
    
  4. Confirm that the location has been updated by running great_expectations store list.

    Notice the output contains two Expectation stores: the original expectations_store on the local filesystem and the shared_expectations_filesystem_store we just configured. This is ok, since Great Expectations will look for Expectations in the shared_expectations/ folder as long as we set the expectations_store_name variable to shared_expectations_filesystem_store. The config for expectations_store can be removed if you would like.

    great_expectations store list
    
    2 Stores found:
    
    - name: expectations_store
    class_name: ExpectationsStore
    store_backend:
        class_name: TupleFilesystemStoreBackend
        base_directory: expectations/
    
    - name: shared_expectations_filesystem_store
    class_name: ExpectationsStore
    store_backend:
        class_name: TupleFilesystemStoreBackend
        base_directory: shared_expectations/
    
  5. Confirm that Expectations can be read from the new storage location by running great_expectations suite list.

    great_expectations suite list
    
    1 Expectation Suite found:
        - npi_expectations
    

Additional Notes

  • For best practices, we highly recommend that you store Expectations in a version-control system like Git. The JSON format of Expectations will allow for informative diff-statements and effective tracking of modifications. In the example below, 2 changes have been made to npi_expectations. The Expectation `expect_table_column_count_to_equal was changed from 330 to 333 to 331.

    git log -p npi_expectations.json
    
    commit cbc127fb27095364c3c1fcbf6e7f078369b07455
        changed expect_table_column_count_to_equal to 331
    
    diff --git a/great_expectations/expectations/npi_expectations.json b/great_expectations/expectations/npi_expectations.json
    
    --- a/great_expectations/expectations/npi_expectations.json
    +++ b/great_expectations/expectations/npi_expectations.json
    @@ -17,7 +17,7 @@
         {
           "expectation_type": "expect_table_column_count_to_equal",
           "kwargs": {
    -        "value": 333
    +        "value": 331
           }
    commit 05b3c8c1ed35d183bac1717d4877fe13bc574963
      changed expect_table_column_count_to_equal to 333
    
    diff --git a/great_expectations/expectations/npi_expectations.json b/great_expectations/expectations/npi_expectations.json
    --- a/great_expectations/expectations/npi_expectations.json
    +++ b/great_expectations/expectations/npi_expectations.json
         {
           "expectation_type": "expect_table_column_count_to_equal",
           "kwargs": {
    -        "value": 330
    +        "value": 333
           }
    

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