Unique upsert in Datomic

upsert

; create attributes p and q, where p is unique identity

(d/transact edb1 {:tx-data [{:db/ident :p :db/cardinality :db.cardinality/one :db/valueType :db.type/keyword :db/unique :db.unique/identity}]})
=>
(d/transact edb1 {:tx-data [{:db/ident :q :db/cardinality :db.cardinality/one :db/valueType :db.type/keyword}]})
=>

; now add a datum

(d/transact edb1 {:tx-data [{:p :a1 :q :x}]})
=>

; and another with a different :p

(d/transact edb1 {:tx-data [{:p :a2 :q :x}]})
=>

; let's have a look:

(d/q '{:find [(pull ?e [*])] :where [[?e :p]]} (d/db edb1))
=>
[[{:db/id 37216269576962135, :p :a1, :q :x}]
 [{:db/id 5286451906347096, :p :a2, :q :x}]]
 
; there they are 
 
; now let's transact a different :q for the same value of :p

(d/transact edb1 {:tx-data [{:p :a1 :q :y}]})
=>

; (all is well)

(d/q '{:find [(pull ?e [*])] :where [[?e :p]]} (d/db edb1))
=>
[[{:db/id 37216269576962135, :p :a1, :q :y}]
 [{:db/id 5286451906347096, :p :a2, :q :x}]]
 
; that same entity 37216269576962135 now has a :q of :y not :x
; let's upsert again: 
 
(d/transact edb1 {:tx-data [{:p :a1 :q :z}]})
=>


(d/q '{:find [(pull ?e [*])] :where [[?e :p]]} (d/db edb1))
=>
[[{:db/id 37216269576962135, :p :a1, :q :z}]
 [{:db/id 5286451906347096, :p :a2, :q :x}]]
 
; again it updates

; now let's try to upsert the same entity with two conflicting assertions:

(d/transact edb1 {:tx-data [{:p :a1 :q :z} {:p :a1 :q :w}]})
ExceptionInfo Two datoms in the same transaction conflict: {:d1 #datom[37216269576962135 79 :z 13194139533352 true], :d2 #datom[37216269576962135 79 :w 13194139533352 true]}  clojure.core/ex-info (core.clj:4739)

; because those two datums had conflicting values in the same transaction - split that into 2 separate transactions if that's what you want

; next let's look at :db.unique/value

; add an attibute :r which is unique by value

(d/transact edb1 {:tx-data [{:db/ident :r :db/cardinality :db.cardinality/one :db/valueType :db.type/keyword :db/unique :db.unique/value}]})
=>

; and assert that there's an the :r of entity with :p :a2 is :x

(d/transact edb1 {:tx-data [{:p :a2 :r :x}]})
=>

; let's try the same thing with the entity with :p :a1

(d/transact edb1 {:tx-data [{:p :a1 :r :x}]})
ExceptionInfo Unique conflict: :r, value: :x already held by: 5286451906347096 asserted for: 37216269576962135  clojure.core/ex-info (core.clj:4739)

; no - there can be only one with :r :x

; now let's see what happens without unique identity

; we'll add an attribute :s which doesn't have :db/unique :db.unique/identity

(d/transact edb1 {:tx-data [{:db/ident :s :db/cardinality :db.cardinality/one :db/valueType :db.type/keyword}]})
=>

; now assert something with a :s on it

(d/transact edb1 {:tx-data [{:s :x :q :x}]})
=>

; let's have a look what we've got:

(d/q '{:find [(pull ?e [*])] :where [[?e :q]]} (d/db edb1))
=>
[[{:db/id 37216269576962135, :p :a1, :q :z}]
 [{:db/id 5286451906347096, :p :a2, :q :x, :r :x}]
 [{:db/id 54298282226090073, :q :x, :s :x}]]
 
; there it is, 54298282226090073, along with the previous things 

; what happens when we assert that again ?

(d/transact edb1 {:tx-data [{:s :x :q :x}]})
=>


(d/q '{:find [(pull ?e [*])] :where [[?e :q]]} (d/db edb1))
=>
[[{:db/id 37216269576962135, :p :a1, :q :z}]
 [{:db/id 5286451906347096, :p :a2, :q :x, :r :x}]
 [{:db/id 54298282226090073, :q :x, :s :x}]
 [{:db/id 54047593574957146, :q :x, :s :x}]]
 
; because :s isn't unique identity, there's no upsert so we get multiple datums 

; let's have another:
 
(d/transact edb1 {:tx-data [{:s :x :q :y}]})
=>

(d/q '{:find [(pull ?e [*])] :where [[?e :q]]} (d/db edb1))
=>
[[{:db/id 12208977114824795, :q :y, :s :x}]
 [{:db/id 37216269576962135, :p :a1, :q :z}]
 [{:db/id 5286451906347096, :p :a2, :q :x, :r :x}]
 [{:db/id 54298282226090073, :q :x, :s :x}]
 [{:db/id 54047593574957146, :q :x, :s :x}]]

; and so on - we can have as many as we like