Write a data contract

Last modified on 23-Sep-24

Soda data contracts is a Python library that uses checks to verify data. Contracts enforce data quality standards in a data pipeline so as to prevent negative downstream impact. To verify the data quality standards for a dataset, you prepare a data contract YAML file, which is a formal description of the data. In the data contract, you use checks to define your expectations for good-quality data. Using the Python API, you can add data contract verification ideally right after new data has been produced.

Be aware, Soda data contracts checks do not use SodaCL.

In your data pipeline, add a data contract after data has been produced or transformed so that when you programmatically run a scan via the Python API, Soda data contracts verifies the contract, executing the checks contained within the contract and producing results which indicate whether the checks passed or failed.

dataset: dim_customer

filter_sql: |
  created > ${FILTER_START_TIME}

owner: zaynabissa@company.com

columns:
- name: last_name
  data_type: character varying
  checks:
  - type: no_missing_values
  - type: no_duplicate_values
  - type: no_invalid_values
    valid_regex: '^(?:[A-Z])$'
- name: total_children
  data_type: integer
  checks:
  - type: avg
    must_be_between: [2, 10]
- name: country_id
  checks:
  - type: invalid_percent
    valid_values_column:
      dataset: COUNTRIES
      column: id
    must_be_less_than: 5
- name: date_first_purchase
  checks:
  - type: freshness_in_hours
    must_be_less_than: 6

checks:
- type: rows_exist
- type: no_duplicate_values
  columns: ['phone', 'email']

✖️    Requires Soda Core Scientific
✔️    Experimentally supported in Soda Core 3.3.3 or greater for PostgreSQL, Snowflake, and Spark
✖️    Supported in Soda Core CLI
✖️    Supported in Soda Library + Soda Cloud
✖️    Supported in Soda Cloud Agreements + Soda Agent

✖️    Available as a no-code check

Prepare a data contract
(Optional) Add YAML code completion in VS Code
(Optional) Add YAML code completion in PyCharm
List of contract configuration keys
Go further

Prepare a data contract

1. After completing the Soda data contracts install requirements, use a code or text editor to create a new YAML file name dim_customer.contract.yml.
2. In the dim_customer.contract.yml file, define the schema, or list of columns, that a data contract must verify, and any data contract checks you wish to enforce for your dataset. At a minimum, you must include the following required parameters; refer to List of configuration keys below.

    # an identifier for the table or view in the SQL data source
    dataset: dim_customer
   
    # a list of columns that represents the dataset's schema, 
    # each of which is identified by the name of a column  
    # in the SQL data source
    columns: 
    - name: first_name
    - name: last_name
    - name: birthdate
   

3. Optionally, you can include any of the following parameters in the file. Refer to Data contracts check reference for a complete list of available checks.

    dataset: dim_customer
   
    # a filter to verify a partition of data
    filter_sql: |
      created > ${FILTER_START_TIME}
   
    columns: 
    - name: first_name
      # an optional parameter to verify the expected type of data in a column
      data_type: character varying
      # an optional parameter to indicate that a column in a schema is not required
      optional: true
    - name: last_name
      # a list of data contract checks that apply to the column, 
      # each of which is identified by a type parameter
      checks:
      - type: no_missing_values
      - type: no_duplicate_values
    - name: birthdate
       
    # a data contract check that applies to the entire dataset
    checks:
    - type: rows_exist
   

4. Save the file, then reference it when you add a contract verification step to your programmatic Soda scan; see Verify a data contract.

Organize your data contracts

Best practice dictates that you structure your data contracts files in a way that resembles the structure of your data source.

1. In your root git repository folder, create a soda folder.
2. In the soda folder, create one folder per data source, then add a data source.yml file in each.
3. In each data source folder, create folders in each schema, then add the contract files in the schema folders.

+ soda
|  + postgres_local
|  |  + data_source.yml
|  |  + public
|  |  |  + customers.yml
|  |  |  + suppliers.yml
|  + snowflake_sales
|  |  data_source.yml
|  |  + RAW
|  |  |  + opportunities.yml
|  |  |  + contacts.yml
+ README.md 

(Optional) Add YAML code completion in VS Code

1. If you have not already done so, install the Red Hat VS Code YAML extension.
2. From the public soda-core repo, download the ./soda/contracts/soda_data_contract_schema_1_0_0.json to a local folder that contains, or will contain, your contract YAML files.
3. Add the following yaml-language-server details to the top of your contract YAML file. You can supply a relative file path for the $schema which the extension determines according to the YAML file path, not from the workspace root path.

    # yaml-language-server: $schema=./soda_data_contract_schema_1_0_0.json
       
    dataset: CUSTOMERS
   
    owner: zaynabissa@company.com
       
    columns:
    - name: id
      data_type: VARCHAR
      checks:
      - type: duplicate_count
   

Alternatively, access instructions to create your own auto-completion.

(Optional) Add YAML code completion in PyCharm

1. Choose an extension for your contract files. For example .contract.yml
2. From the public soda-core repo, download the ./soda/contracts/soda_data_contract_schema_1_0_0.json to a local drive that also contains, or will contain, your contract YAML files.
3. In your PyCharm environment, navigate to Preferences > Languages & Frameworks > Schemas and DTDs > JSON Schema Mappings.
4. Add a mapping between the extensions you chose in step 1. For example, use *.contract.yml files and map to the schema file that you saved on your local file system.

See also: Using custom JSON schemas.

List of configuration keys

Threshold boundaries

When you use must_be_between threshold keys, Soda includes the boundary values as acceptable. In the following example, a check result of 100 or 120 each passes.

dataset: dim_customer

columns:
- name: first_name
- name: middle_name
- name: last_name

checks:
- type: row_count
  must_be_between: [100, 120]

When you use must_be_between threshold keys, Soda includes the boundary values as acceptable. In the following example, a check result of 0 or 120 each fails.

dataset: dim_customer

columns:
- name: first_name
- name: middle_name
- name: last_name

checks:
- type: row_count
  must_be_not_between: [0, 120]

Use multiple thresholds to adjust the inclusion of boundary values.

dataset: dim_customer

columns:
- name: total_children
  # check passes if values are outside the range, inclusive of 20 
  checks:
  - type: avg
    must_be_less_than: 10
    must_be_greater_than_or_equal_to: 20
- name: yearly_income
  # check passes if values are inside the range, inclusive of 100
  checks:
  - type: avg
    must_be_greater_than_or_equal_to: 100
    must_be_less_than: 200

Leverage Soda YAML extensibility

Because the Soda data contract YAML is extensible, you can add your own custom configuration parameters to a data contract YAML file for other tools in your data stack to use. Soda data contracts ignores these custom keys during verification.

For example, you may wish to include a parameter to identify a dataset’s owner, or to identify role-based access that another tool enforces.

dataset: dim_product

owner: zaynabissa@company.com

# Configure parameters for other tools to use.
# Soda data contract verification ignores this parameter.
default_column_view_roles: 
- admin 
- product_mgr

# Soda data contract verification ignores this parameter.
sensitive_column_view_roles: 
- admin 

columns:
- name: discount_percent
  # Soda data contract verification ignores this parameter.
  sensitive: true

Go further

• Next: Verify a data contract.
• Need help? Join the Soda community on Slack.
  

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Documentation always applies to the latest version of Soda products
Last modified on 23-Sep-24

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