Add dummy references for spec-gen

[mitchkyle-reify]

Add the ability to generate non-nil values for references in spec-gen using :reifyhealth.specmonstah.core/dummy.

The use case I have for this is I have a table with a composite key primary key (id and version) and I need to be able to insert values into it that reference other row ids in same table but still generate the ids for ones that do not reference another row.

With this patch I satisfy my use case in the following way:

  (require '[clojure.spec.alpha :as s])
  (require '[reifyhealth.specmonstah
             [core :as sm]
             [spec-gen :as sg]])
  (s/def ::id uuid?)
  (s/def ::version int?)
  (s/def ::value string?)
  (s/def ::versioned-datum (s/keys :req-un [::id ::version ::value]))
  (sg/ent-db-spec-gen-attr {:schema
                            {:my-table {:spec      ::versioned-datum
                                        :relations {:id [:my-table :id]}
                                        :prefix    :mt}}}
                           {:my-table [[:first-version
                                        {:refs     {:id ::sm/dummy}
                                         :spec-gen {:version 1}}]
                                       [:second-version
                                        {:refs     {:id :first-version}
                                         :spec-gen {:version 2}}]]})

  =>
  {:first-version
   {:id #uuid "4a010cb7-bdfb-4f64-abfa-bb719eb16ca1",
    :version 1,
    :value "Jt3"},
   :second-version
   {:id #uuid "4a010cb7-bdfb-4f64-abfa-bb719eb16ca1",
    :version 2,
    :value "KA222fJFxdMuvv"}}

There might be a better way to solve this, I'm open to ideas.

[mitchkyle-reify]

An alternative to thinking of this as "dummy references" with ::sm/dummy we could think of them as "self references" and call the key ::sm/self. This wouldn't be a functional difference, just a semantic one.

[flyingmachine]

@mitchkyle-reify I wanted to check in on this, were you able to accomplish what you needed?

[mitchkyle-reify]

Yes, my use case is satisfied by fixing the bug with self references #88 thanks for checking in.