columnDefaultValue

columnDefaultValue is a custom policy check that ensures new columns do not have default values explicity listed.

Learn how to create and customize the columnDefaultValue Liquibase Custom Policy Check using a Python script.

This example was tested on Oracle. You can use this check as it is or customize it further to fit your needs in your SQL database.

For a conceptual overview of this feature, see Liquibase Pro Custom Policy Checks.

Scope	Database
database	Oracle

Step-by-step

These steps describe how to create the Custom Policy Check. It does not exist by default in Liquibase Pro.

1. Create a Check Settings file: Use the Checks Settings Configuration File

2. Add this code to your Checks Settings file:

   Copy

   columnDefaultValue Python Script

   ###
   ### This script ensures new columns do not have default values explicity listed
   ###
   ### Notes:
   ### 1. Only basic ALTER table statements are supported
   ### 2. Single and multiple columns in an alter statement *are* supported
   ###
   
   ###
   ### Helpers come from Liquibase
   ###
   import sys
   import liquibase_utilities
   
   ###
   ### Functions
   ###
   
   ###
   ### Retrieve log handler
   ### Ex. liquibase_logger.info(message)
   ###
   liquibase_logger = liquibase_utilities.get_logger()
   
   ###
   ### Retrieve status handler
   ###
   liquibase_status = liquibase_utilities.get_status()
   
   ###
   ### Retrieve all changes in changeset
   ###
   changes = liquibase_utilities.get_changeset().getChanges()
   
   ###
   ### Loop through all changes
   ###
   for change in changes:
       ###
       ### LoadData change types are not currently supported
       ###
       if "loaddatachange" in change.getClass().getSimpleName().lower():
           liquibase_logger.info("LoadData change type not supported. Statement skipped.")
           continue
       ###
       ### Retrieve sql as string, remove extra whitespace
       ###
       raw_sql = liquibase_utilities.strip_comments(liquibase_utilities.generate_sql(change)).casefold()
       raw_sql = " ".join(raw_sql.split())
       ###
       ### Split sql into statements
       ###
       raw_statements = liquibase_utilities.split_statements(raw_sql)
       for raw_statement in raw_statements:
           ###
           ### Split raw_statement into list, look for alter table, remove schema if provided
           ###
           sql_list = raw_statement.split()
           try:
               if sql_list[0] == "alter" and sql_list[1] == "table" and sql_list[3] == "add":
                   ### Table name
                   table_name = sql_list[2].split(".")[-1]
                   start = table_name.rfind("(")
                   if start != -1:
                       table_name = table_name[0:start]
               else:
                   raise UserWarning
           except (IndexError, ValueError):
               liquibase_logger.warning(f"Unsupported Alter statement skipped: {raw_statement}")
               continue
           except UserWarning:
               liquibase_logger.info(f"Non Alter statement skipped: {raw_statement}")
               continue
           ###
           ### ALTER
           ###
           found = False
           search_string = " add ("
           start = raw_statement.find(search_string)
           ###
           ### ALTER TABLE NAME ADD column type [DEFAULT value]
           ###
           if start == -1:
               if raw_statement.find("default") != -1:
                   found = True
                   column_name = sql_list[4]
           ###
           ### ALTER TABLE NAME ADD (column1 type1 [DEFAULT value1], column2 type2, [DEFAULT value2], ...)
           ###
           else:
               start += len(search_string)
               end = raw_statement.rfind(")")
               if end != -1:
                   column_list = raw_statement[start:end].split(",")
                   for column in column_list:
                       if "default" in column:
                           found = True
                           column_name = column.split()[0].strip()
           ###
           ### Report matches
           ###
           if found == True:
               liquibase_status.fired = True
               status_message = str(liquibase_utilities.get_script_message()).replace("__COLUMN_NAME__", f"\"{column_name}\"")
               status_message = status_message.replace("__TABLE_NAME__", f"\"{table_name}\"")
               liquibase_status.message = status_message
               sys.exit(1)
   
   ###
   ### Default return code
   ###
   False

3. Initiate the customization process. In the CLI, run this command:
   liquibase checks customize --check-name=CustomCheckTemplate
   The CLI prompts you to finish configuring your file. A message displays:

   This check cannot be customized directly because one or more fields does not have a default value.

   Liquibase will then create a copy of CustomCheckTemplate and initiate the customization workflow.

4. Give your check a short name so you can easily identify what Python script it is associated with (up to 64 alpha-numeric characters only).
   In this example we will name the check:
   columnDefaultValue

5. Set the Severity to return a code of 0-4 when triggered. These severity codes allow you to determine if the job moves forward or stops when this check triggers.
   Learn more here: Use Policy Checks in Automation: Severity and Exit Code
   options: 'INFO'=0, 'MINOR'=1, 'MAJOR'=2, 'CRITICAL'=3, 'BLOCKER'=4

6. Set SCRIPT_DESCRIPTION. In this example, we will set the description to:

   This script ensures new columns do not have default values explicity listed.

7. Set SCRIPT_SCOPE. In this example, we will set the scope to changelog. The Python sample provided in this tutorial requires it.
• changelog: for example, if your check looks for syntax patterns or attributes in your Liquibase Changelog (the changes you author in your repository). With this value, the check runs once per changeset.
8. Set the SCRIPT_MESSAGE. This message will display when the check is triggered. In this example we will use:
   This script identified that Column __COLUMN_NAME__ in table __TABLE_NAME__ should not have a default value.
9. Set the SCRIPT_PATH. This is the relative path where your script is stored in relation to the changelog specified in --changelog-file, whether it is stored locally or in a repository.
   In this example, we will set the path to: scripts/column-default-value.py.
10. This check does not need a SCRIPT_ARGUMENT, so leave it blank.
11. Set the REQUIRES_SNAPSHOT. If your script scope is changelog, set whether the check requires a database snapshot. Specify true if your check needs to inspect database objects. (If your script scope is database, Liquibase always takes a snapshot, so this prompt does not appear.)

Note: The larger your database, the more performance impact a snapshot causes. If you cannot run a snapshot due to memory limitations, see Memory Limits of Inspecting Large Schemas.

You have now successfully created and customized a policy check!

Next steps

• Run a Custom Policy Check

Related Topics

Sample Custom Policy Check Scripts