RESTful way to create multiple items in one request

Question

I believe that another correct way to approach this would be to create another resource that represents your collection of resources. Example, imagine that we have an endpoint like /api/sheep/{id} and we can POST to /api/sheep to create a sheep resource.

Now, if we want to support bulk creation, we should consider a new flock resource at /api/flock (or /api/<your-resource>-collection if you lack a better meaningful name). Remember that resources don't need to map to your database or app models. This is a common misconception.

Resources are a higher level representation, unrelated with your data. Operating on a resource can have significant side effects, like firing an alert to a user, updating other related data, initiating a long lived process, etc. For example, we could map a file system or even the unix ps command as a REST API.

I think it is safe to assume that operating a resource may also mean to create several other entities as a side effect.

Although bulk operations (e.g. batch create) are essential in many systems, they are not formally addressed by the RESTful architecture style.

I found that POSTing a collection as you suggested basically works, but problems arise when you need to report failures in response to such a request. Such problems are worse when multiple failures occur for different causes or when the server doesn't support transactions. My suggestion to you is that if there is no performance problem, for example when the service provider is on the LAN (not WAN) or the data is relatively small, it's worth it to send 100 POST requests to the server. Keep it simple, start with separate requests and if you have a performance problem try to optimize.

Facebook explains how to do this: https://developers.facebook.com/docs/graph-api/making-multiple-requests

Simple batched requests

The batch API takes in an array of logical HTTP requests represented as JSON arrays - each request has a method (corresponding to HTTP method GET/PUT/POST/DELETE etc.), a relative_url (the portion of the URL after graph.facebook.com), optional headers array (corresponding to HTTP headers) and an optional body (for POST and PUT requests). The Batch API returns an array of logical HTTP responses represented as JSON arrays - each response has a status code, an optional headers array and an optional body (which is a JSON encoded string).

Your idea seems valid to me. The implementation is a matter of your preference. You can use JSON or just parameters for this ("order_lines[]" array) and do

POST /orders

Since you are going to create more resources at once in a single action (order and its lines) it's vital to validate each and every of them and save them only if all of them pass validation, ie. you should do it in a transaction.

I've actually been wrestling with this lately, and here's what I'm working towards.

If a POST that adds multiple resources succeeds, return a 200 OK (I was considering a 201, but the user ultimately doesn't land on a resource that was created) along with a page that displays all resources that were added, either in read-only or editable fashion. For instance, a user is able to select and POST multiple images to a gallery using a form comprising only a single file input. If the POST request succeeds in its entirety the user is presented with a set of forms for each image resource representation created that allows them to specify more details about each (name, description, etc).

In the event that one or more resources fails to be created, the POST handler aborts all processing and appends each individual error message to an array. Then, a 419 Conflict is returned and the user is routed to a 419 Conflict error page that presents the contents of the error array, as well as a way back to the form that was submitted.

I guess it's better to send separate requests within single connection. Of course, your web-server should support it