# ERD Table Nodes

> Design a database schema on a whiteboard, with real primary/foreign keys and crow's-foot cardinality.

Source: https://docs.docgraph.app/whiteboards/erd/

Whiteboards include a dedicated **table node** for entity-relationship diagrams — sketch a schema right next to the notes that explain it, and link the two together.

*[Screenshot: Three connected ERD tables — sites, observers, and records — with primary and foreign keys marked and one relationship showing crow's-foot cardinality.]*

## Building a table

The dock's **Table** tool adds a table node seeded with three starter columns, ready to rename into your own schema.

- **Rename the table** — double-click its title.
- **Add a column** — the **+ Add column** button at the bottom of the table.
- **Rename a column, or change its type** — double-click the name or the type cell independently; each commits on Enter. Type is free text (`uuid`, `text`, `int`, `varchar(255)`, anything you want) — there's no fixed type list to pick from.
- **Mark a primary or foreign key** — the small icon button on the left of each row cycles through **plain → primary key → foreign key → plain** on each click.
- **Reorder columns** — drag the grip handle on the left of a row.
- **Color the table** — select it and pick a swatch from the style panel's palette; the color tints the table's header.
- **Remove a column** — the ✕ on the right of a row. If another table has a relationship pointing at that exact column, the connection doesn't break — it re-anchors to the table as a whole.

## Connecting tables

Every table exposes a connection handle on **each column**, on both sides — plus the usual four handles on the table's header, for a plain table-to-table link that isn't anchored to any particular column. Drag from one handle to another to draw a relationship; it's the same drag gesture as connecting any other kind of node on the canvas.

## Cardinality (crow's-foot notation)

Select a relationship edge to open its style panel, which includes two independent dropdowns — **From (ERD)** and **To (ERD)** — one for each end of the line. Each end can be set to **Plain, One, Many, Zero or one, One or many,** or **Zero or many**, so you compose whatever cardinality the relationship actually has rather than picking from a short fixed list.

*[Screenshot: The edge-style panel with From (ERD) set to Many and To (ERD) set to One.]*

DocGraph draws the matching glyph at each end of the line — a bar for "one":

*[Screenshot: A single bar glyph marking the "one" end of a relationship, next to a primary key.]*

— and a crow's-foot for "many":

*[Screenshot: A forked crow's-foot glyph marking the "many" end of a relationship, next to a foreign key.]*

## What "connected" means here

Dragging a connection between two handles always works — DocGraph doesn't check that a `uuid` column only links to another `uuid` column, or enforce any other notion of "compatible" endpoints. What it does guarantee is file integrity: a foreign-key edge always resolves to a real column on a real table, and if that column is later renamed that's fine (edges track the column's identity, not its label) — it's only removed entirely that re-anchors the edge to the table itself rather than leaving it dangling.

## Let AI draft it

You can describe a schema in plain language in [chat](https://docs.docgraph.app/ai/chat/) and have the assistant build the tables, columns, and foreign-key relationships for you — including setting cardinality. It's the same confirmation-gated agent that edits your notes, just aimed at a whiteboard instead.

The same works from outside the app. Connect Claude Code, Cursor or any MCP client to DocGraph and ask it for the schema; it authors the `.wb` through the `create_board` tool and extends it later with `edit_board`. See [Author a diagram from Claude Code](https://docs.docgraph.app/ai/mcp/#author-a-diagram-from-claude-code).