Create

The create interaction creates a new resource with a server-assigned id. If the client wishes to have control over the id of a newly submitted resource, it should use the update interaction instead.

POST [base]/[type]

NOTE

Blaze runs all writes as transactions one at a time in a single total order (actual serial execution). A transaction can only start once the previous one has finished, so a large transaction blocks all smaller ones — including this create — until it completes. See Actual Serial Execution for details.

The request body has to be a resource of the same type as the [type] in the URL. If the types don't match or the body is missing, Blaze returns a 400 Bad Request with an OperationOutcome. Any id, meta.versionId and meta.lastUpdated values in the request body are ignored. All other elements of meta like meta.source are preserved.

On success, Blaze returns a 201 Created with an ETag header containing the version id of the resource, a Last-Modified header and a Location header with the version-specific URL of the newly created resource:

HTTP/1.1 201 Created
Location: [base]/[type]/[id]/_history/[vid]
Last-Modified: Tue, 24 Jun 2025 09:03:22 GMT
ETag: W/"23"

By default, the response body contains the created resource. This can be controlled with the Prefer header:

Value	Description
return=representation	Return the created resource (default).
return=minimal	Return no body.
return=OperationOutcome	Return an OperationOutcome instead of the resource.

Referential Integrity

By default, Blaze enforces referential integrity, so all resources referenced by the resource to create have to exist already. Otherwise, Blaze returns a 409 Conflict with an OperationOutcome. That behaviour can be changed by setting the environment variable ENFORCE_REFERENTIAL_INTEGRITY to false.

Conditional Create

Blaze supports the conditional create via an If-None-Exist header containing the search parameters that should be used to check for existing resources:

If-None-Exist: identifier=095156

The outcome depends on the number of resources matching the search:

Matches	Description
none	The resource is created and a 201 Created is returned.
one	No new resource is created. The already existing resource is returned with a 200 OK.
many	Blaze returns a 412 Precondition Failed with an OperationOutcome and doesn't create a resource.

The search and the potential creation are executed in the same transaction, so conditional creates are safe against concurrent requests. An empty If-None-Exist header or one containing only ignorable search parameters like _sort results in a normal, unconditional create.

Conditional create can also be used in transaction and batch requests via Bundle.entry.request.ifNoneExist. However, references to already existing resources currently can't be resolved. If you need this feature, please vote on the issue Implement Conditional References.