Your first Datastore

In the last section, we made a HTTP request that created a 404. We'll use the trace of that HTTP request to build an endpoint, a technique we call Trace Driven Development.

  1. Hit the plus (+) button in the 404 section of the sidebar. This creates a HTTP endpoint with the HTTP verb (POST) and path (/test) set from the request that creates the 404.


  1. Hover over the white dot on the left hand side. Here, you can see the full body of the incoming trace from when you posted to the endpoint from the REPL, including the body.


  1. Let's save the request body to a variable by typing let data = request.body. As you can see, the autocomplete knows the field names of request from the trace, and will complete them for you.


  1. Let's put this in a datastore. Like we saw with the HttpClient library, typing "DB" in the blank will pull up all datastore functions.


In this case, we want DB::set, which takes three arguments.


  1. Now let's make our datastore. From the sidebar or the omnibox, create a new datastore called "Requests", with fields data and time.


Dark's datastores are key-value stores; each record has a unique key that is used to store and retrieve the value. For instance, a possible set of records with keys in the above datastore would look like this:

key1: {
data: {
test: "test2"
time: <Date: 2020-02-11T18:54:39Z>
key2: {
data: {
test: "test1"
time: <Date: 2020-02-11T18:54:43Z>
  1. Now that we have a datastore, let's finish our post endpoint.

    The first argument is the record we're inserting. This needs to match the schema, and so it needs to include both date and time (you cannot insert records that are missing fields). Insert our data from above (seeing the live value to the left) and use the Date::now function to get the time field.


  1. We need a unique key for each record that we store. The DB::generateKey function generates random keys – this is useful when your record has no obvious unique identifier.


  1. The final argument is the Datastore: Requests.


  1. To call the DB::set function, we first need to run the two functions with side effects (DB::generateKey and Date::now) by hitting the play button. After hitting those two play buttons, the DB::set play button will be enabled:


  1. Finally, hitting the play button for DB::set inserts the record into the datastore. This locks the datastore, preventing us from changing the schema, which we see indicated by the red lock (🔒) icon.