How to use Great Expectations with Amazon Web Services using Athena
Great Expectations is aware that the fluent datasource and yaml config workflows are undocumented. A new method for connecting to data sources will be added to this topic soon. In the meantime, use the Great Expectations Slack channel if you encounter issues and need assistance.
Great Expectations can work within many frameworks. In this guide you will be shown a workflow for using Great Expectations with AWS and cloud storage. You will configure a local Great Expectations project to store Expectations, Validation Results, and Data Docs in Amazon S3 buckets. You will further configure Great Expectations to access data stored in an Athena database.
This guide will demonstrate each of the steps necessary to go from installing a new instance of Great Expectations to Validating your data for the first time and viewing your Validation Results as Data Docs.
Prerequisites
- Python 3. To download and install Python, see Python downloads.
- The AWS CLI. To download and install the AWS CLI, see Installing or updating the latest version of the AWS CLI.
- AWS credentials. See Configuring the AWS CLI.
-
Permissions to install the Python packages (
boto3
andgreat_expectations
) with pip. - An S3 bucket and prefix to store Expectations and Validation Results.
Steps
Part 1: Setup
1.1 Ensure that the AWS CLI is ready for use
1.1.1 Verify that the AWS CLI is installed
You can verify that the AWS CLI has been installed by running the command:
aws --version
If this command does not respond by informing you of the version information of the AWS CLI, you may need to install the AWS CLI or otherwise troubleshoot your current installation. For detailed guidance on how to do this, please refer to Amazon's documentation on how to install the AWS CLI)
1.1.2 Verify that your AWS credentials are properly configured
Run the following command in the AWS CLI to verify that your AWS credentials are properly configured:
aws sts get-caller-identity
When your credentials are properly configured, your
UserId
, Account
and
Arn
are returned. If your credentials are
not configured correctly, an error message appears.
If an error message appears, or if you couldn't use the AWS CLI to verify your credentials configuration, see Configuring the AWS CLI.
1.2 Prepare a local installation of Great Expectations
1.2.1 Verify that your Python version meets requirements
First, check the version of Python that you have installed. As of this writing, Great Expectations supports versions 3.7 through 3.10 of Python.
You can check your version of Python by running:
python --version
If this command returns something other than a Python 3 version number (like Python 3.X.X), you may need to try this:
python3 --version
If you do not have Python 3 installed, please refer to python.org for the necessary downloads and guidance to perform the installation.
1.2.2 Create a virtual environment for your Great Expectations project
Once you have confirmed that Python 3 is installed
locally, you can create a virtual environment with
venv
before installing your packages with
pip
.
Python Virtual Environments
Depending on whether you found that you needed to run
python
or python3
in the
previous step, you will create your virtual
environment by running either:
python -m venv my_venv
or
python3 -m venv my_venv
This command will create a new directory called
my_venv
where your virtual environment is
located. In order to activate the virtual environment
run:
source my_venv/bin/activate
You can name your virtual environment anything you
like. Simply replace my_venv
in the
examples above with the name that you would like
to use.
1.2.3 Ensure you have the latest version of pip
Once your virtual environment is activated, you should ensure that you have the latest version of pip installed.
Pip is a tool that is used to easily install Python packages. If you have Python 3 installed you can ensure that you have the latest version of pip by running either:
python -m ensurepip --upgrade
or
python3 -m ensurepip --upgrade
1.2.4 Install boto3
Python interacts with AWS through the
boto3
library. Great Expectations makes
use of this library in the background when working
with AWS. Although you won't use
boto3
directly, you'll need to
install it in your virtual environment.
Run one of the following pip commands to install
boto3
in your virtual environment:
python -m pip install boto3
or
python3 -m pip install boto3
To set up
boto3
with AWS, and use boto3
from within
Python, see the
Boto3 documentation.
1.2.5 Install Great Expectations
You can use pip to install Great Expectations by running the appropriate pip command below:
python -m pip install great_expectations
or
python3 -m pip install great_expectations
1.2.6 Verify that Great Expectations installed successfully
You can confirm that installation worked by running:
great_expectations --version
This should return something like:
great_expectations, version 0.16.15
1.3 Create your Data Context
For purposes of this example, we will assume that we have an empty folder to initialize our Filesystem Data Context in:
path_to_empty_folder = '/my_gx_project/'
We will provide our empty folder's path to the GX
library's
FileDataContext.create(...)
method as the
project_root_dir
parameter. Because we
are providing a path to an empty folder
FileDataContext.create(...)
will
initialize a Filesystem Data Context at that location.
For convenience, the
FileDataContext.create(...)
method will
then instantiate and return the newly initialized Data
Context, which we can keep in a Python variable.
from great_expectations.data_context import FileDataContext
context = FileDataContext.create(project_root_dir=path_to_empty_folder)
1.4 Configure your Expectations Store on Amazon S3
1.4.1 Identify your Data Context Expectations Store
Your Expectation StoreA connector to store and retrieve information about collections of verifiable assertions about data. configuration is in your Data ContextThe primary entry point for a Great Expectations deployment, with configurations and methods for all supporting components..
The following section in your
Data ContextThe primary entry point for a Great Expectations
deployment, with configurations and methods for
all supporting components.
great_expectations.yml
file tells Great
Expectations to look for Expectations in a Store named
expectations_store
:
stores:
expectations_store:
class_name: ExpectationsStore
store_backend:
class_name: TupleFilesystemStoreBackend
base_directory: expectations/
expectations_store_name: expectations_store
The default base_directory
for
expectations_store
is
expectations/
.
1.4.2 Update your configuration file to include a new Store for Expectations on Amazon S3
To manually add an
Expectations StoreA connector to store and retrieve information
about collections of verifiable assertions about
data.
to your configuration, add the following configuration
to the stores
section of your
great_expectations.yml
file:
stores:
expectations_S3_store:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: <your>
prefix: <your>
expectations_store_name: expectations_S3_store
As shown in the previous example, you need to change
the default store_backend
settings to
make the Store work with S3. The
class_name
is set to
TupleS3StoreBackend
,
bucket
is the address of your S3 bucket,
and prefix
is the folder in your S3
bucket where Expectations are located.
The following example shows the additional options
that are available to customize
TupleS3StoreBackend
:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
endpoint_url: ${S3_ENDPOINT} # Uses the S3_ENDPOINT environment variable to determine which endpoint to use.
region_name: '<your_aws_region_name>'
In the previous example, the Store name is
expectations_S3_store
. If you use a
personalized Store name, you must also update the
value of the expectations_store_name
key
to match the Store name. For example:
expectations_store_name: expectations_S3_store
When you update the
expectations_store_name
key value, Great
Expectations uses the new Store for Validation
Results.
Add the following code to
great_expectations.yml
to configure the
IAM user:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
aws_access_key_id: ${AWS_ACCESS_KEY_ID} # Uses the AWS_ACCESS_KEY_ID environment variable to get aws_access_key_id.
aws_secret_access_key: ${AWS_ACCESS_KEY_ID}
aws_session_token: ${AWS_ACCESS_KEY_ID}
Add the following code to
great_expectations.yml
to configure the
IAM Assume Role:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
assume_role_arn: '<your_role_to_assume>'
region_name: '<your_aws_region_name>'
assume_role_duration: session_duration_in_seconds
If you are also storing
Validations in S3
or
DataDocs in S3, make sure that the prefix
values
are disjoint and one is not a substring of the
other.
1.4.3 Verify that the new Amazon S3 Expectations Store has been added successfully
You can verify that your Stores are properly configured by running the command:
great_expectations store list
This will list the currently configured Stores that
Great Expectations has access to. If you added a new
S3 Expectations Store, the output should include the
following ExpectationsStore
entry:
- name: expectations_S3_store
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
Notice the output contains only one Expectation Store:
your configuration contains the original
expectations_store
on the local
filesystem and the
expectations_S3_store
we just configured,
but the
great_expectations store list
command
only lists your active stores. For your Expectation
Store, this is the one that you set as the value of
the expectations_store_name
variable in
the configuration file:
expectations_S3_store
.
1.4.4 (Optional) Copy existing Expectation JSON files to the Amazon S3 bucket
If you are converting an existing local Great Expectations deployment to one that works in AWS, you might have Expectations saved that you want to transfer to your S3 bucket.
To copy Expectations into Amazon S3, use the
aws s3 sync
command as shown in the
following example:
aws s3 sync '<base_directory>' s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'
The base_directory
is set to
expectations/
by default.
In the following example, the Expectations
exp1
and exp2
are copied to
Amazon S3 and a confirmation message is returned:
upload: ./exp1.json to s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'/exp1.json
upload: ./exp2.json to s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'/exp2.json
1.4.5 (Optional) Verify that copied Expectations can be accessed from Amazon S3
If you copied your existing Expectation Suites to the S3 bucket, run the following Python code to confirm that Great Expectations can find them:
import great_expectations as gx
context = gx.get_context()
context.list_expectation_suite_names()
The Expectations you copied to S3 are returned as a list. Expectations that weren't copied to the new Store aren't listed.
1.5 Configure your Validation Results Store on Amazon S3
1.5.1 Identify your Data Context's Validation Results Store
Your Validation Results StoreA connector to store and retrieve information about objects generated when data is Validated against an Expectation Suite. configuration is in your Data ContextThe primary entry point for a Great Expectations deployment, with configurations and methods for all supporting components..
The following section in your
Data ContextThe primary entry point for a Great Expectations
deployment, with configurations and methods for
all supporting components.
great_expectations.yml
file tells Great
Expectations to look for Validation Results in a Store
named validations_store
. It also creates
a ValidationsStore
named
validations_store
that is backed by a
Filesystem and stores Validation Results under the
base_directory
uncommitted/validations
(the default).
stores:
validations_store:
class_name: ValidationsStore
store_backend:
class_name: TupleFilesystemStoreBackend
base_directory: uncommitted/validations/
validations_store_name: validations_store
1.5.2 Update your configuration file to include a new Store for Validation Results on Amazon S3
To manually add a Validation Results Store, add the
following configuration to the
stores
section of your
great_expectations.yml
file:
stores:
validations_S3_store:
class_name: ValidationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: <your>
prefix: <your>
As shown in the previous example, you need to change
the default store_backend
settings to
make the Store work with S3. The
class_name
is set to
TupleS3StoreBackend
,
bucket
is the address of your S3 bucket,
and prefix
is the folder in your S3
bucket where Validation Results are located.
The following example shows the additional options
that are available to customize
TupleS3StoreBackend
:
class_name: ValidationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
endpoint_url: ${S3_ENDPOINT} # Uses the S3_ENDPOINT environment variable to determine which endpoint to use.
region_name: '<your_aws_region_name>'
In the previous example, the Store name is
validations_S3_store
. If you use a
personalized Store name, you must also update the
value of the validations_store_name
key
to match the Store name. For example:
validations_store_name: validations_S3_store
When you update the
validations_store_name
key value, Great
Expectations uses the new Store for Validation
Results.
Add the following code to
great_expectations.yml
to configure the
IAM user:
class_name: ValidationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
aws_access_key_id: ${AWS_ACCESS_KEY_ID} # Uses the AWS_ACCESS_KEY_ID environment variable to get aws_access_key_id.
aws_secret_access_key: ${AWS_ACCESS_KEY_ID}
aws_session_token: ${AWS_ACCESS_KEY_ID}
Add the following code to
great_expectations.yml
to configure the
IAM Assume Role:
class_name: ValidationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
assume_role_arn: '<your_role_to_assume>'
region_name: '<your_aws_region_name>'
assume_role_duration: session_duration_in_seconds
If you are also storing
ExpectationsA verifiable assertion about data.
in S3 (How to configure an Expectation store to use
Amazon S3), or DataDocs in S3 (How to host and share Data Docs on Amazon S3), then make sure the prefix
values
are disjoint and one is not a substring of the
other.
1.5.3 Verify that the new Amazon S3 Validation Results Store has been added successfully
To make Great Expectations look for Validation Results
in an S3 bucket, set the
validations_store_name
variable in
great_expectations.yml
to the name of
your S3 Validations Store as shown in the following
example:
class_name: ValidationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
endpoint_url: ${S3_ENDPOINT} # Uses the S3_ENDPOINT environment variable to determine which endpoint to use.
region_name: '<your_aws_region_name>'
Add the following code to
great_expectations.yml
to configure the
IAM user:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
aws_access_key_id: ${AWS_ACCESS_KEY_ID} # Uses the AWS_ACCESS_KEY_ID environment variable to get aws_access_key_id.
aws_secret_access_key: ${AWS_ACCESS_KEY_ID}
aws_session_token: ${AWS_ACCESS_KEY_ID}
Add the following code to
great_expectations.yml
to configure the
IAM Assume Role:
class_name: ExpectationsStore
store_backend:
class_name: TupleS3StoreBackend
bucket: '<your_s3_bucket_name>'
prefix: '<your_s3_bucket_folder_name>'
boto3_options:
assume_role_arn: '<your_role_to_assume>'
region_name: '<your_aws_region_name>'
assume_role_duration: session_duration_in_seconds
1.5.4 (Optional) Copy existing Validation results to the Amazon S3 bucket
If you are converting an existing local Great Expectations deployment to one that works in AWS, you might have Validation Results saved that you want to transfer to your S3 bucket.
To copy Validation Results into Amazon S3, use the
aws s3 sync
command as shown in the
following example:
aws s3 sync '<base_directory>' s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'
The base_directory
is set to
uncommitted/validations/
by default.
In the following example, the Validation Results
Validation1
and
Validation2
are copied to Amazon S3 and a
confirmation message is returned:
upload: uncommitted/validations/val1/val1.json to s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'/val1.json
upload: uncommitted/validations/val2/val2.json to s3://'<your_s3_bucket_name>'/'<your_s3_bucket_folder_name>'/val2.json
1.6 Configure Data Docs for hosting and sharing from Amazon S3
1.6.1 Create an Amazon S3 bucket for your Data Docs
You can create an S3 bucket configured for a specific location using the AWS CLI. Make sure you modify the bucket name and region for your situation.
> aws s3api create-bucket --bucket data-docs.my_org --region us-east-1
{
"Location": "/data-docs.my_org"
}
1.6.2 Configure your bucket policy to enable appropriate access
The example policy below
enforces IP-based access - modify the
bucket name and IP addresses for your situation. After
you have customized the example policy to suit your
situation, save it to a file called
ip-policy.json
in your local directory.
Your policy should provide access only to appropriate users. Data Docs sites can include critical information about raw data and should generally not be publicly accessible.
{
"Version": "2012-10-17",
"Statement": [{
"Sid": "Allow only based on source IP",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": [
"arn:aws:s3:::data-docs.my_org",
"arn:aws:s3:::data-docs.my_org/*"
],
"Condition": {
"IpAddress": {
"aws:SourceIp": [
"192.168.0.1/32",
"2001:db8:1234:1234::/64"
]
}
}
}
]
}
Because Data Docs include multiple generated
pages, it is important to include the
arn:aws:s3:::{your_data_docs_site}/*
path in the Resource
list along with
the
arn:aws:s3:::{your_data_docs_site}
path that permits access to your Data Docs'
front page.
Amazon Web Service's S3 buckets are a third party utility. For more (and the most up to date) information on configuring AWS S3 bucket policies, please refer to Amazon's guide on using bucket policies.
1.6.3 Apply the access policy to your Data Docs' Amazon S3 bucket
Run the following AWS CLI command to apply the policy:
> aws s3api put-bucket-policy --bucket data-docs.my_org --policy file://ip-policy.json
1.6.4 Add a new Amazon S3 site to the
data_docs_sites
section of your
great_expectations.yml
The below example shows the default
local_site
configuration that you will
find in your great_expectations.yml
file,
followed by the s3_site
configuration
that you will need to add. You may optionally remove
the default local_site
configuration
completely and replace it with the new
s3_site
configuration if you would only
like to maintain a single S3 Data Docs site.
data_docs_sites:
local_site:
class_name: SiteBuilder
show_how_to_buttons: true
store_backend:
class_name: TupleFilesystemStoreBackend
base_directory: uncommitted/data_docs/local_site/
site_index_builder:
class_name: DefaultSiteIndexBuilder
S3_site: # this is a user-selected name - you may select your own
class_name: SiteBuilder
store_backend:
class_name: TupleS3StoreBackend
bucket: <your>
site_index_builder:
class_name: DefaultSiteIndexBuilder
1.6.5 Test that your Data Docs configuration is correct by building the site
Use the following command:
context.build_data_docs()
to build and
open your newly configured S3 Data Docs site.
context.build_data_docs()
Additional notes on hosting Data Docs from an Amazon S3 bucket
-
Optionally, you may wish to update static hosting settings for your bucket to enable AWS to automatically serve your index.html file or a custom error file:
> aws s3 website s3://data-docs.my_org/ --index-document index.html
-
If you wish to host a Data Docs site in a subfolder of an S3 bucket, add the
prefix
property to the configuration snippet in step 4, immediately after thebucket
property. -
If you wish to host a Data Docs site through a private DNS, you can configure a
base_public_path
for the Data Docs StoreA connector to store and retrieve information pertaining to Human readable documentation generated from Great Expectations metadata detailing Expectations, Validation Results, etc.. The following example will configure a S3 site with thebase_public_path
set towww.mydns.com
. Data Docs will still be written to the configured location on S3 (for examplehttps://s3.amazonaws.com/data-docs.my_org/docs/index.html
), but you will be able to access the pages from your DNS (http://www.mydns.com/index.html
in our example)data_docs_sites:
s3_site: # this is a user-selected name - you may select your own
class_name: SiteBuilder
store_backend:
class_name: TupleS3StoreBackend
bucket: data-docs.my_org # UPDATE the bucket name here to match the bucket you configured above.
base_public_path: http://www.mydns.com
site_index_builder:
class_name: DefaultSiteIndexBuilder
show_cta_footer: true
Part 2: Connect to data
2.1 Choose how to run the code for creating a new Datasource
The previous sections of this guide involved manually editing configuration files to add configurations for Amazon S3 buckets. When setting up your Datasource configurations, it is simpler to use Great Expectation's Python API. We recommend doing this from a Jupyter Notebook, as you will then receive immediate feedback on the results of your code blocks. However, you can alternatively use a Python script in the IDE of your choice.
If you would like, you may use the Great Expectations CLICommand Line Interface to automatically generate a pre-configured Jupyter Notebook. To do so, run the following console command from the root directory of your Great Expectations project:
great_expectations datasource new
Once you have your pre-configured Jupyter Notebook, you should follow along in the YAML-based workflow in the following steps.
If you choose to work from a blank Jupyter Notebook or a Python script, you may find it easier to use the following Python dictionary workflow over the YAML workflow. Great Expectations supports either configuration method.
2.2 Instantiate your project's DataContext
Import these necessary packages and modules.
import great_expectations as gx
from great_expectations.core.batch import Batch, BatchRequest, RuntimeBatchRequest
from great_expectations.core.yaml_handler import YAMLHandler
yaml = YAMLHandler()
Load your DataContext into memory using the
get_context()
method.
context = gx.get_context()
2.3 Configure your Datasource
2.3.1 Determine your connection string
In order for Great Expectations to connect to Athena, you will need to provide a connection string. To determine your connection string, reference the examples below and the PyAthena documentation.
As of this writing, Great Expectations is not compatible with SQLAlchemy version 2 or greater. We recommend using the latest non-version-2 release.
The following urls don't include credentials as it is recommended to use either the instance profile or the boto3 configuration file.
If you want Great Expectations to connect to your Athena instance (without specifying a particular database), the URL should be:
awsathena+rest://@athena.{region}.amazonaws.com/?s3_staging_dir={s3_path}
Note the url parameter "s3_staging_dir" needed for storing query results in S3.
If you want Great Expectations to connect to a particular database inside your Athena, the URL should be:
awsathena+rest://@athena.{region}.amazonaws.com/{database}?s3_staging_dir={s3_path}
credentials
instead of
connection_string
The credentials
key uses a dictionary
to provide the elements of your connection string
as separate, individual values. For information on
how to populate the
credentials
dictionary and how to
configure your
great_expectations.yml
project config
file to populate credentials from either a YAML
file or a secret manager, please see our guide on
How to configure credentials.
2.3.2 Create your Datasource configuration
Using the following example configuration, add in the
CONNECTION_STRING
for your database:
- YAML
- Python
datasource_yaml = f"""
name: my_awsathena_datasource
class_name: Datasource
execution_engine:
class_name: SqlAlchemyExecutionEngine
module_name: great_expectations.execution_engine
connection_string: {connection_string}
data_connectors:
default_runtime_data_connector_name:
class_name: RuntimeDataConnector
batch_identifiers:
- default_identifier_name
module_name: great_expectations.datasource.data_connector
default_inferred_data_connector_name:
class_name: InferredAssetSqlDataConnector
module_name: great_expectations.datasource.data_connector
include_schema_name: true
"""
datasource_dict = {
"name": "my_awsathena_datasource",
"class_name": "Datasource",
"execution_engine": {
"class_name": "SqlAlchemyExecutionEngine",
"module_name": "great_expectations.execution_engine",
"connection_string": connection_string,
},
"data_connectors": {
"default_runtime_data_connector_name": {
"class_name": "RuntimeDataConnector",
"batch_identifiers": ["default_identifier_name"],
"module_name": "great_expectations.datasource.data_connector",
},
"default_inferred_data_connector_name": {
"class_name": "InferredAssetSqlDataConnector",
"module_name": "great_expectations.datasource.data_connector",
"include_schema_name": "true",
},
},
}
To configure a SQL datasource such as the one used to connect to your Athena data, see How to configure a SQL Datasource
2.4 Save the Datasource configuration to your DataContext
Save the configuration into your
DataContext
by using the
add_datasource()
function.
- YAML
- Python
context.add_datasource(**yaml.load(datasource_yaml))
context.add_datasource(**datasource_config)
2.5 Test your new Datasource
First, create a Batch Request.
batch_request = {
"datasource_name": "my_awsathena_datasource",
"data_connector_name": "default_inferred_data_connector_name",
"data_asset_name": f"{ATHENA_DB_NAME}.taxitable",
"limit": 1000,
}
Next, prepare an empty Expectation suite.
expectation_suite_name = "version-0.16.16 my_awsathena_expectation_suite"
try:
suite = context.get_expectation_suite(expectation_suite_name=expectation_suite_name)
print(
f'Loaded ExpectationSuite "{suite.expectation_suite_name}" containing {len(suite.expectations)} expectations.'
)
except DataContextError:
suite = context.add_expectation_suite(expectation_suite_name=expectation_suite_name)
print(f'Created ExpectationSuite "{suite.expectation_suite_name}".')
Now you can load data into a Validator
.
If this is successful then you will have verified that
your Datasource is working properly.
validator = context.get_validator(
batch_request=BatchRequest(**batch_request),
expectation_suite_name=expectation_suite_name,
)
validator.head(n_rows=5, fetch_all=False)
Part 3: Create Expectations
3.1: Prepare a Batch Request, empty Expectation Suite, and Validator
When we tested our Datasource in step 2.5: Test your new Datasource we also created all of the components we need to begin creating Expectations: A Batch Request to provide sample data we can test our new Expectations against, an empty Expectation Suite to contain our new Expectations, and a Validator to create those Expectations with.
We can reuse those components now. Alternatively, you
may follow the same process that we did before and
define a new Batch Request, Expectation Suite, and
Validator if you wish to use a different Batch of data
as the reference sample when you are creating
Expectations or if you wish to use a different name
than test_suite
for your Expectation
Suite.
3.2: Use a Validator to add Expectations to the Expectation Suite
There are many Expectations available for you to use. To demonstrate creating an Expectation through the use of the Validator we defined earlier, here are examples of the process for two of them:
validator.expect_column_values_to_not_be_null(column="passenger_count")
validator.expect_column_values_to_be_between(
column="congestion_surcharge", min_value=0, max_value=1000
)
Each time you evaluate an Expectation (e.g. via
validator.expect_*
) two things will
happen. First, the Expectation will immediately be
Validated against your provided Batch of data. This
instant feedback helps to zero in on unexpected data
very quickly, taking a lot of the guesswork out of
data exploration. Second, the Expectation
configuration will be stored in the Expectation Suite
you provided when the Validator was initialized.
You can also create Expectation Suites using a Data Assistant to automatically create expectations based on your data or manually using domain knowledge and without inspecting data directly.
To find out more about the available Expectations, please see our Expectations Gallery.
3.3: Save the Expectation Suite
When you have run all of the Expectations you want for
this dataset, you can call
validator.save_expectation_suite()
to
save the Expectation Suite (all of the unique
Expectation Configurations from each run of
validator.expect_*
)for later use in a
Checkpoint.
validator.save_expectation_suite(discard_failed_expectations=False)
Part 4: Validate Data
4.1: Create and run a Checkpoint
Here we will create and store a CheckpointThe primary means for validating data in a production deployment of Great Expectations. for our Batch, which we can use to validate and run post-validation ActionsA Python class with a run method that takes a Validation Result and does something with it.
Checkpoints are a robust resource that can be preconfigured with a Batch Request and Expectation Suite or take them in as parameters at runtime. They can also execute numerous Actions based on the Validation Results that are returned when the Checkpoint is run.
This guide will demonstrate using a
SimpleCheckpoint
that takes in a Batch
Request and Expectation Suite as parameters for the
context.run_checkpoint(...)
command.
For more information on pre-configuring a Checkpoint with a Batch Request and Expectation Suite, please see our guides on Checkpoints.
4.1.1 Create a Checkpoint
First we create the Checkpoint configuration:
- YAML
- Python
my_checkpoint_name = "version-0.16.16 insert_your_checkpoint_name_here"
my_checkpoint_config = f"""
name: {my_checkpoint_name}
config_version: 1.0
class_name: SimpleCheckpoint
run_name_template: "%Y%m%d-%H%M%S-my-run-name-template"
"""
my_checkpoint_name = "version-0.16.16 my_databricks_checkpoint"
checkpoint = SimpleCheckpoint(
name=my_checkpoint_name,
config_version=1.0,
class_name="version-0.16.16 SimpleCheckpoint",
run_name_template="%Y%m%d-%H%M%S-my-run-name-template",
data_context=context,
)
Once we have defined our Checkpoint configuration, we
can test our syntax using
context.test_yaml_config(...)
:
- YAML
my_checkpoint = context.test_yaml_config(my_checkpoint_config)
Note that we get a message that the Checkpoint
contains no validations. This is OK because we will
pass them in at runtime, as we can see below when we
call context.run_checkpoint(...)
.
4.1.2 Save the Checkpoint
We can now add the Checkpoint to our Data Context:
context.add_or_update_checkpoint(checkpoint)
4.1.3 Run the Checkpoint
Finally, having added our Checkpoint to our Data Context, we will run the Checkpoint:
checkpoint_result = checkpoint.run()
4.2: Build and view Data Docs
Since we used a SimpleCheckpoint
, our
Checkpoint already contained an
UpdateDataDocsAction
which rendered our
Data DocsHuman readable documentation generated from Great
Expectations metadata detailing Expectations,
Validation Results, etc.
from the Validation Results we just generated. That
means our Data Docs store will contain a new entry for
the rendered Validation Result.
For more information on Actions that Checkpoints can perform and how to add them, please see our guides on Actions.
Viewing this new entry is as simple as running:
context.open_data_docs()
Congratulations!
🚀🚀 Congratulations! 🚀🚀 You have successfully navigated the entire workflow for using Great Expectations with Amazon Web Services and Athena, from installing Great Expectations through Validating your Data.