---
id: STORE-4
family: GR-STORE
level: core
profiles: [storage-api]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-store/store-4
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# STORE-4 — Absent collections default to empty, and an update touches only what it sends

*GR-STORE (Part I) · level: core · profiles: storage-api · added in 1.0*

An update is partial. What a caller does not send, it does not change, which is what lets an editor save one part of a workflow without holding the whole of it.

## The rule

> **Normative.** This is the rule.
>
> 1. On create, `nodes`, `edges` and `metadata` default to the empty list when absent, and a workflow that declares no `interface` declares no ports.
>
> 2. On update, a key the request omits is left as stored; `name` is the exception, required on update as on create.
>
> 3. An `interface` present on update rewrites both port lists from it even when only one side is supplied, so a missing or empty `inputs` or `outputs` clears that side.
>
> 4. The `metadata` published on read need not be identical to the `metadata` as stored: an implementation may fold envelope fields such as `format` and `schemaVersion` back into it on read.


## What it means

An update is partial by default: a key the request does not send is left as
stored, which is what lets a caller save one part of a workflow without
holding the whole of it in hand. `interface` is the one key where "sent"
does not mean "sent in full" — sending it at all rewrites both the inputs
and the outputs it describes, even if only one of them is included. A side
left out of a present `interface`, or sent as an empty list, is cleared, not
left alone. Absent and empty are the same signal there that they are not
everywhere else in this rule: absent preserves, present (even partially or
emptily) replaces.

The `metadata` a caller reads back is not necessarily the `metadata` it
would get by reading the stored document directly: an implementation may
fold housekeeping fields such as a format marker or a schema version into
what it publishes on read, without those fields having been part of what was
stored.

## Example

Three requests to the same door, none of them touching `interface` the same
way.

```http title="A create with no nodes, edges or metadata" verdict="201 stored"
POST /api/flowdrop/workflows

{"id": "bare_wf", "name": "Bare"}
```

```http title="An update naming only the name and the nodes" verdict="200 preserved"
PUT /api/flowdrop/workflows/{workflow}

{"name": "Partial renamed", "nodes": [ … ]}
```

```http title="An update whose interface is present but empty" verdict="200 cleared"
PUT /api/flowdrop/workflows/{workflow}

{"name": "Clear", "interface": []}
```

The first leaves `nodes`, `edges` and `metadata` all as empty lists — nothing
was sent for them, so there is nothing to default from but empty. The second
leaves the edges and metadata a prior request had set untouched, because
this request never mentions them. The third is the one that reads like the
second but is not: `interface` was sent, so both its sides are rewritten, and
an empty list on either side clears it rather than leaving it as it was.

## Related rules

- Names: STORE-2, STORE-14
- Referenced by: STORE-14

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.