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Version: 1.2.3

Connect to SQL data

To connect to your SQL data, you first create a Data Source which tells GX where your database resides and how to connect to it. You then configure Data Assets for your Data Source to tell GX which sets of records you want to be able to access from your Data Source. Finally, you will define Batch Definitions which allow you to request all the records retrieved from a Data Asset or further partition the returned records based on the contents of a date and time field.

GX supports the following SQL dialects:

  • PostgreSQL
  • SQLite
  • Snowflake
  • Databricks SQL
  • BigQuery SQL

All other SQL dialects are handled through the python module SQLAlchemy. You can find more information on the dialects supported by SQLAlchemy on their dialects page.

Configure credentials​

To connect GX to your SQL data, you will need your connection string and corresponding credentials. Because your connection string and credentials provide access to your data they should be stored securely outside of version control. GX Core allows you to securely store credentials and connection strings as environment variables or in an uncommitted config file. These variables are then accessed through string substitution in your version controlled code.

Prerequisites​

  • The ability to set environment variables or a File Data Context.

GX Core also supports referencing credentials that have been stored in the AWS Secrets Manager, Google Cloud Secret Manager, and Azure Key Vault secrets managers. To set up GX Core to access one of these secrets managers you will additionally require:

  • The ability to install Python modules with pip.

Procedure​

  1. Determine your connection string format.

    Different types of SQL database have different formats for their connection string. In the following table, the text in <> corresponds to the values specific to your credentials and connection string.

    Database typeConnection string
    PostgreSQLpostgresql+psycopg2://<USERNAME>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>
    SQLitesqlite:///<PATH_TO_DB_FILE>
    Snowflakesnowflake://<USER_NAME>:<PASSWORD>@<ACCOUNT_NAME>/<DATABASE_NAME>/<SCHEMA_NAME>?warehouse=<WAREHOUSE_NAME>&role=<ROLE_NAME>&application=great_expectations_oss
    Databricks SQLdatabricks://token:<TOKEN>@<HOST>:<PORT>?http_path=<HTTP_PATH>&catalog=<CATALOG>&schema=<SCHEMA>
    BigQuery SQLbigquery://<GCP_PROJECT>/<BIGQUERY_DATASET>?credentials_path=/path/to/your/credentials.json

    Other connection string formats are valid provided they are for a SQL database that is supported by SQLAlchemy. You can find more information on the dialects supported by SQLAlchemy on their dialects page.

  2. Store the credentials required for your connection string.

    GX supports the following methods of securely storing credentials. Chose one to implement for your connection string:

    Environment variables provide the quickest way to securely set up your credentials.

    You can set environment variables by replacing the values in <> with your information and entering export <VARIABLE_NAME>=<VALUE> commands in the terminal or adding the commands to your ~/.bashrc file. If you use the export command from the terminal, the environment variables will not persist beyond the current session. If you add them to the ~/.bashrc file, the variables will be exported each time you log in.

    You can export individual credentials or an entire connection string. For example:

    Terminal or ~/.bashrc
    export MY_POSTGRES_USERNAME=<USERNAME>
    export MY_POSTGRES_PASSWORD=<PASSWORD>

    or:

    Terminal or ~/.bashrc
    export POSTGRES_CONNECTION_STRING=postgresql+psycopg2://<USERNAME>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>

    You can also reference your stored credentials within a stored connection string by wrapping their corresponding variable in ${ and }. For example:

    Terminal or ~/.bashrc
    export MY_POSTGRES_USERNAME=<USERNAME>
    export MY_POSTGRES_PASSWORD=<PASSWORD>
    export POSTGRES_CONNECTION_STRING=postgresql+psycopg2://${MY_POSTGRES_USERNAME}:${MY_POSTGRES_PASSWORD}@<HOST>:<PORT>/<DATABASE>

    Because the dollar sign character $ is used to indicate the start of a string substitution they should be escaped using a backslash \ if they are part of your credentials. For example, if your password is pa$$word then in the previous examples you would use the command:

    Terminal or ~/.bashrc
    export MY_POSTGRES_PASSWORD=pa\$\$word

  3. Access your credentials in Python strings.

    Securely stored credentials are accessed via string substitution. You can reference your credentials in a Python string by wrapping the variable name in ${ and }. Using individual credentials would look like:

    Python
    connection_string="postgresql+psycopg2://${MY_POSTGRES_USERNAME}:${MY_POSTGRES_PASSWORD}@${POSTGRES_HOST}:${POSTGRES_PORT}/${POSTGRES_DATABASE}",

    Or you could reference a configured variable that contains the full connection string by providing a Python string that contains just a reference to that variable:

    Python
    connection_string="${POSTGRES_CONNECTION_STRING}"

    When you pass a string that references your stored credentials to a GX Core method that requires a connection string as a parameter the referenced variable will be substituted for the corresponding stored value.

  4. Optional. Access credentials stored in a secret manager.

    GX Core supports the AWS Secrets Manager, Google Cloud Secret Manager, and Azure Key Vault secrets managers. For more information on how to set up string substitutions that pull credentials from these sources, see Access secrets managers.

Create a SQL Data Source​

Data Sources tell GX where your data is located and how to connect to it. With SQL databases this is done through a connection string you will provide.

Prerequisites​

Procedure​

  1. Import GX and instantiate a Data Context:

    Python
    import great_expectations as gx

    context = gx.get_context()

  2. Define a name and connection string for your Data Source.

    You can assign any name to a Data Source as long as it is unique within your Data Context.

    Your connection string or credentials should not be saved in plain text in your code. Instead, you should reference a securely stored connection string or credentials through string substitution. The guidance on how to Configure your credentials covers how to determine the format of your connection string, securely store your connection string or credentials, and how to reference your connection string or credentials in Python.

    The following code defines a Data Source name and references a PostgreSQL connection string that has been securely stored in its entirety:

    Python
    datasource_name = "my_new_datasource"
    my_connection_string = "${POSTGRESQL_CONNECTION_STRING}"

  3. Create a Data Source.

    GX Core provides specific methods for creating Data Sources that correspond to supported SQL dialects. All of these methods are accessible from the data_sources attribute of your Data Context. Reference the following table to determine the method used for your data's SQL dialect:

    Database typeData Context method
    PostgreSQLcontext.data_sources.add_postgres(name: str, connection_string: str)
    SQLitecontext.data_sources.add_sqlite(name: str, connection_string: str)
    Snowflakecontext.data_sources.add_snowflake(name:str, connection_string: str)
    DataBricks SQLcontext.data_sources.add_databricks_sql(name: str, connection_string: str)
    Other SQLcontext.data_sources.add_sql(name: str, connection_string:str)

    Once you have the method for your data's SQL dialect, you can call it with the previously defined Data Source name and connection string to create your Data Source. The following example creates a PostgreSQL Data Source:

    Python
    data_source = context.data_sources.add_postgres(
        name=datasource_name, connection_string=my_connection_string
    )

  4. Optional. Verify the Data Source is connected:

    Python
    print(context.data_sources.get(datasource_name))

    The details of your Data Source are retrieved from the Data Context and displayed.

Create a Data Asset​

Data Assets are collections of records within a Data Source. With SQL Data Sources, a Data Asset can consist of the records from a specific table or the records from a specified query.

Prerequisites​

Procedure​

  1. Retrieve your Data Source.

    Replace the value of data_source_name with the name of your Data Source and execute the following code to retrieve an existing Data Source from your Data Context:

    Python
    data_source_name = "my_new_datasource"
    data_source = context.data_sources.get(data_source_name)

  2. Add a Data Asset to your Data Source.

    A Table Data Asset consists of the records in a single table. It takes two required parameters:

    • table_name: The name of the SQL table that the Table Data Asset will retrieve records from.
    • name: The name used to reference the Table Data Asset within GX. You may assign this arbitrarily, but all Data Assets within the same Data Source must have unique names.

    Replace the values of asset_name and database_table_name in the following code, then execute it to add a Table Data Asset to your Data Source:

    Python
    asset_name = "MY_TABLE_ASSET"
    database_table_name = "postgres_taxi_data"
    table_data_asset = data_source.add_table_asset(
        table_name=database_table_name, name=asset_name
    )

  3. Optional. Verify that your Data Asset was added to your Data Source:

    print(data_source.assets)

    A list of Data Assets is printed. You can verify your Data Asset was created and added to the Data Source by checking for its name in the printed list.

  4. Optional. Add additional Data Assets to your Data Source.

    A Data Source can have multiple Data Assets. Repeat this procedure to add additional Table or Query Data Assets to your Data Source.

Create a Batch Definition​

A Batch Definition allows you to request all the records from a Data Asset or a subset based on the contents of a date and time field.

For API-managed Expectations only

If you use GX Cloud and GX Core together, note that Batch Definitions you create with the API apply to API-managed Expectations only.

Prerequisites​

Procedure​

  1. Retrieve your Data Asset.

    Replace the value of datasource_name with the name of your Data Source and the value of asset_name with the name of your Data Asset in the following code. Then execute it to retrieve an existing Data Source and Data Asset from your Data Context:

    Python
    # Retrieve a Data Source
    datasource_name = "my_datasource"
    data_source = context.data_sources.get(datasource_name)

    # Get the Data Asset from the Data Source
    asset_name = "MY_TABLE_ASSET"
    data_asset = data_source.get_asset(asset_name)

  2. Add a Batch Definition to the Data Asset.

    A full table Batch Definition returns all of the records in your Data Asset as a single Batch. Therefore, to define a full table Batch Definition you only need to provide a name for the Batch Definition to be referenced by.

    Update the name parameter and execute the following code to create a full table Batch Definition:

    Python
    full_table_batch_definition = data_asset.add_batch_definition_whole_table(
        name="FULL_TABLE"
    )

  3. Optional. Verify the Batch Definition is valid.

    When retrieving a Batch from a partitioned Batch Definition, you can specify the date of the data to retrieve as shown in the following examples. If you do not specify a date, the most recent date in the data is returned by default.

    Python
    full_table_batch = full_table_batch_definition.get_batch()
    full_table_batch.head()

  4. Optional. Create additional Batch Definitions.

    A Data Asset can have multiple Batch Definitions as long as each Batch Definition has a unique name within that Data Asset. Repeat this procedure to add additional full table or partitioned Batch Definitions to your Data Asset.