05 progressive construction

At the beginning of this tutorial, I told you that add-ents takes an potato db as an argument:

(dc/add-ents {:schema potato-schema} {:post [{:count 1}]})

You may have wondered why don’t just pass in the potato-schema alone as the first argument, like this:

(dc/add-ents potato-schema {:post [{:count 1}]})

The reason the first argument to add-ents is a potato db and not a potato schema is so you can take the return value of add-ents and pass it in as the first argument to further calls to add-ents:

(ns donut.datapotato-tutorial.05
  (:require [donut.datapotato.core :as dc]))

(def potato-schema
  {:user  {:prefix :u}
   :topic {:prefix    :t
           :relations {:owner-id [:user :id]}}})

(def potato-db
  {:schema potato-schema})

(defn ex-01
  []
  (let [potato-db-1 (dc/add-ents {:schema potato-schema} {:topic [{:count 1}]})
        potato-db-2 (dc/add-ents potato-db-1 {:topic [{:count 1}
                                                      {:refs {:owner-id :hamburglar}}]})]
    (dc/view potato-db-1)
    (dc/view potato-db-2)))

(ex-01)

Additional calls to add-ents are additive; they will never alter existing ents, and will only add new ents. The first call, (dc/add-ents {:schema schema} {:topic [{:count 1}]}), produces a :topic named :t0 referencing a :user named :u0:

That potato db is passed to the next call:

(dc/add-ents ent-db-1 {:topic [{:count 1}
                               {:refs {:owner-id :hamburglar}}]})

This creates two more topics:


The default naming system picks up where it left off, giving the topic the names :t1 and :t2. :t1 references the existing user, :u0, and :t2 references a new user from the :refs, :hamburglar. When progressively generating an ent-db, you can expect datapotato to behave as if all queries were passed as a single query to a single call of add-ents.

Everything you’ve learned up to this point has focused on generating an potato db: you’ve learned a bit about how to use schemas and queries together to concisely specify what ents to create. You’ve also learned how to customize the relationships with the :refs query option.

In the next couple sections, you’ll learn about how datapotato uses visitation to generate and insert business data.

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