Known Issues and Future Work

pgmock has quite a few limitations and issues, some that will be addressed and some things that are not possible to implement because of limitations in the postgres VALUES expressions. These are discussed here along with future work to address issues and make pgmock better.

General Parsing Issues

pgmock relies on regular expressions to speedily find and patch relevant SQL expressions. This has limitations with parsing nested parentheses and pgmock implements this with custom code.

Using special characters/words in string literals and comments can cause issues for the regular expressions. For example, this would cause issues when parsing statements since a semicolon is in the comments:

-- I'm a comment that has a semicolon ; in it

For now, pgmock addresses this issue by allowing safe mode to be turned on (pgmock.config.set_safe_mode) or by passing safe_mode=True to pgmock.sql or pgmock.sql_file. This mode will strip all SQL of any string literals or comments to make searching more accurate, but it comes at a cost of performance. In some cases for really large SQL, performance can be impacted by 50 - 100X slowdowns in pgmock’s selector performance. While this time is still rather small in the context of a test that hits a database, it should be taken into account when using safe mode.

Other Known Issues

Here’s a short list of some other known issues:

  • Subqueries without an alias are currently not supported (e.g. an IN expression). Future versions of pgmock plan to address this.
  • Joins where another keyword comes after the join are currently not supported (e.g. JOIN LATERAL), but future versions plan to address this.
  • Using the replace_new_patch_aliases mode (see pgmock.config.set_replace_new_patch_aliases) will not work when using double quotes around selected columns (e.g. SELECT "schema"."table"."column" FROM ...)