11: collection constraint (vector of foreign keys)
Let's say the forum you're building stores a user's favorite posts as a vector of foreign keys, like this:
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{:username "birb"
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:favorite-ids [1 2 3 4]}
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Here's how you'd model this in Specmonstah:
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(ns reifyhealth.specmonstah-tutorial.11
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(:require [clojure.spec.alpha :as s]
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[reifyhealth.specmonstah.core :as sm]
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[reifyhealth.specmonstah.spec-gen :as sg]))
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​
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(s/def ::id (s/and pos-int? #(< % 100)))
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​
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(s/def ::post (s/keys :req-un [::id]))
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​
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(s/def ::favorite-ids (s/coll-of ::id))
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(s/def ::user (s/keys :req-un [::id ::favorite-ids]))
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​
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(def schema
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{:post {:prefix :p
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:spec ::post}
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:user {:prefix :u
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:spec ::user
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:relations {:favorite-ids [:post :id]}
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:constraints {:favorite-ids #{:coll}}}})
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There's our buddy
:constraints again :) This time the constraint is :coll. This is used by the clojure.spec visitor to generate data correctly:1
(defn ex-01
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[]
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(sg/ent-db-spec-gen-attr {:schema schema} {:user [[1]]}))
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​
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(ex-01) ;; =>
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{:p0 {:id 6}
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:u0 {:id 9, :favorite-ids [6]}}
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Specmonstah generated a post with
:id 6, and sure enough you can see that the value of :favorite-ids is a vector containing the post's :id. But what if you want to generate multiple posts? Here's how you'd do that:1
(defn ex-02
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[]
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(sg/ent-db-spec-gen-attr {:schema schema}
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{:user [[1 {:refs {:favorite-ids 3}}]]}))
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(ex-02)
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;; =>
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{:p0 {:id 6}
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:p1 {:id 21}
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:p2 {:id 8}
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:u0 {:id 1
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:favorite-ids [6 21 8]}}
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And boom goes the dynamite. The key here is the map
{:refs {:favorite-ids 3}} - this tells Specmonstah that this user will have 3 :favorite-ids.You might be wondering, what happens if you generate 2 separate users, each with 3
:favorite-ids? Well my friend, wonder no more:1
(defn ex-03
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[]
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(sm/view (sm/add-ents {:schema schema}
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{:user [[2 {:refs {:favorite-ids 3}}]]})))
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(ex-03)
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Both users reference the same posts because Specmonstah generates the minimum data necessary to satisfy the query. You can also "manually" specify the ents you want to reference:
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(defn ex-04
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[]
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(sm/view (sm/add-ents {:schema schema}
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{:user [[1 {:refs {:favorite-ids [:my-p0 :my-p1]}}]
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[1 {:refs {:favorite-ids [:my-p2 :my-p3]}}]]})))
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(ex-04)
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