We support rudimentary filtering on connections using a condition argument. Currently this allows you to filter for specific values (e.g. username: "Alice" or category: ARTICLE) but more advanced filters are being discussed. It's important when implementing filters to keep performance in mind, for that reason it's likely that version 5 will not expose filters for columns that are not indexed.

Filter Plugin

One of the PostGraphile community members, Matt Bretl, maintains a filter plugin with many advanced filtering capabilities, located at; you might like to check it out.