Use the If-Match HTTP Header in PUT and PATCH operations

For REST endpoints, developers often want control over whether updates create new records or only modify existing ones. The If-Match HTTP header provides that control in Data API builder (DAB).

By default, DAB treats PUT and PATCH as upsert operations:

• If the resource exists: it's updated.

• If it doesn't exist: it's inserted.

  • PUT → full upsert (replaces resource).
  • PATCH → incremental upsert (applies partial update).

Adding If-Match: * changes this behavior to update-only semantics.

What If-Match does in DAB

If-Match is supported only with the wildcard value *.

Header Value	Behavior
If-Match: *	Perform update only if the resource exists; if missing → 404 Not Found.
If-Match: <any other>	Rejected; 400 Bad Request (Etags not supported, use '*').
(absent)	Upsert behavior (insert if not found, otherwise update).

Behavior overview

• DAB doesn't implement per-record ETag or version matching.
• No concurrency token is evaluated. * only asserts "must exist."
• Applies only to REST, not GraphQL.
• Not currently meaningful for DELETE operations.

Using If-Match with PUT

Without If-Match, PUT inserts when the resource doesn't exist (returns 201 Created).

Update-only example

Request

PUT /api/Books/id/1
If-Match: *
Content-Type: application/json

{
  "title": "The Return of the King"
}

Success (record existed)

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 1,
  "title": "The Return of the King"
}

Failure (record missing)

HTTP/1.1 404 Not Found
Content-Type: application/json

{
  "error": "No Update could be performed, record not found"
}

Upsert insert example (no If-Match and record didn't exist)

Request

PUT /api/Books/id/500
Content-Type: application/json

{
  "title": "Inserted via PUT",
  "publisher_id": 7
}

Response

HTTP/1.1 201 Created
Location: id/500
Content-Type: application/json

{
  "id": 500,
  "title": "Inserted via PUT",
  "publisher_id": 7
}

Using If-Match with PATCH

PATCH behaves similarly. Without If-Match, it performs an incremental upsert. With If-Match: *, it only updates existing rows.

Request

PATCH /api/Books/id/1
If-Match: *
Content-Type: application/json

{
  "title": "The Two Towers"
}

Response when Success

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 1,
  "title": "The Two Towers"
}

Response when Not found

HTTP/1.1 404 Not Found
Content-Type: application/json

{
  "error": "No Update could be performed, record not found"
}

Invalid If-Match Usage

Any value other than * (including quoted strings) is rejected.

Request

PUT /api/Books/id/1
If-Match: "abc123"
Content-Type: application/json

{
  "title": "To Kill a Mockingbird"
}

Response

HTTP/1.1 400 Bad Request
Content-Type: application/json

{
  "error": "Etags not supported, use '*'"
}

Review

• Omit If-Match for upsert (insert-or-update) semantics.
• Use If-Match: * for strict update-only semantics (404 if the item is missing).
• Don't use any other value. Real ETag matching isn't implemented.