Entry Meta

This plugin adds the ability to save schemaless metadata to entries and query by that data.

Why?

Sometimes you'll need to attach additional information to your entry without creating a corresponding field in Craft. Common examples include saving an identifier of the entry in another system, keeping track of post views, saving the gclid on a lead, or flagging an entry as seeded for later removal.

One option would be to create a read-only field on Craft using a plugin that allows for hidden/read-only field types. However, there are multiple cons to this approach:

You now have a field in your section layout that does not semantically belong there.
It can be accessed, modified and deleted from the control panel (granted only on dev environment).
It is loaded when creating or editing a post, which can be easily tampered with from the developer console of the browser.
It does not allow for ad-hoc data that could pertain to a single post or just some posts, without creating yet another field.
It is saved to the content table, rather than the entries table, where it naturally belongs.

Entry Meta offers a more flexible, schemaless alternative, which by-passes the user-facing data structure and allows you to save metadata in JSON format directly to the entries table:

Save metadata using dedicated methods on the Entry element.
Flexibly Query metadata (including nested structures) using the Entry active record.
Data displayed on the sidebar along with Craft's metadata.
Supports both MySQL and PostgreSQL