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Allow callers to run functions within the scope of a transaction.

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This generalizes the transactor loop to allow callers to run
an arbitrary function within an `in-transaction!` body.

Combined with exposing `<report-transact-tx-data!`, this allows
an admittedly sophisticated consumer to conditionally query and
transact in a consistent way -- for example, cleaning up inconsistent
data then transacting a new schema version.
This commit is contained in:
Richard Newman 2016-11-01 16:47:47 -07:00
parent bd0a56e501
commit 3212be565c
1 changed files with 52 additions and 28 deletions
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80
src/common/datomish/transact.cljc
View file

@ -791,14 +791,14 @@
(-> report
(assoc-in [:db-after] db-after)))))
(defn- <with [db tx-data]
(defn <transact-tx-data-in-transaction! [db tx-data]
(let [fail-touch-attr (fn [old new] (raise "Altering schema attributes is not yet supported, got " new " altering existing schema attribute " old
{:error :schema/alter-schema :old old :new new}))]
(<with-internal db tx-data fail-touch-attr)))
(defn <db-with [db tx-data]
(defn <db-transact-tx-data! [db tx-data]
(go-pair
(:db-after (<? (<with db tx-data)))))
(:db-after (<? (<transact-tx-data-in-transaction! db tx-data)))))
(defn <transact!
"Submits a transaction to the database for writing.
@ -806,11 +806,15 @@
Returns a pair-chan resolving to `[result error]`."
([conn tx-data]
(<transact! conn tx-data (a/chan 1) true))
([conn tx-data result close?]
([conn tx-data-or-fn result close?]
{:pre [(conn? conn)]}
;; Any race to put! is a real race between callers of <transact!. We can't just park on put!,
;; because the parked putter that is woken is non-deterministic.
(let [closed? (not (a/put! (:transact-chan conn) [:sentinel-transact tx-data result close?]))]
(let [op (if (fn? tx-data-or-fn)
:sentinel-fn
:sentinel-transact)
closed? (not (a/put! (:transact-chan conn)
[op tx-data-or-fn result close?]))]
(go-pair
;; We want to return a pair-chan, no matter what kind of channel result is.
(if closed?
@ -823,30 +827,50 @@
(>! token-chan (gensym "transactor-token"))
(loop []
(when-let [token (<! token-chan)]
(when-let [[sentinel tx-data result close?] (<! (:transact-chan conn))]
(let [pair
(<! (go-pair ;; Catch exceptions, return the pair.
(case sentinel
:sentinel-close
;; Time to close the underlying DB.
(<? (db/close-db @(:current-db conn)))
(when-let [[sentinel tx-data-or-fn result close?] (<! (:transact-chan conn))]
(let
[pair
(<!
(go-pair ;; Catch exceptions, return the pair.
(case sentinel
:sentinel-close
;; Time to close the underlying DB.
(<? (db/close-db @(:current-db conn)))
;; Default: process the transaction.
(do
(when @(:closed? conn)
;; Drain enqueued transactions.
(raise "Connection is closed" {:error :transact/connection-closed}))
(let [db (db conn)
report (<? (db/in-transaction!
db
#(-> (<with db tx-data))))]
(when report
;; <with returns non-nil or throws, but we still check report just in
;; case. Here, in-transaction! function completed and returned non-nil,
;; so the transaction has committed.
(reset! (:current-db conn) (:db-after report))
(>! (:listener-source conn) report))
report)))))]
;; Default: process the transaction.
(do
(when @(:closed? conn)
;; Drain enqueued transactions.
(raise "Connection is closed" {:error :transact/connection-closed}))
(let [db (db conn)
in-transaction-fn
(case sentinel
:sentinel-fn
;; This is a function that we'd like to run
;; within a database transaction. See
;; db/in-transaction! for details.
;; The function is invoked with two arguments:
;; the db and a function that takes (db,
;; tx-data) and transacts it to return a
;; TxReport.
;; The function must return a TxReport.
;; The function must not itself call
;; `in-transaction!` or `<transact!`.
(partial tx-data-or-fn db <transact-tx-data-in-transaction!)
:sentinel-transact
;; This is data. Apply it with `<transact-tx-data-in-transaction!`.
(partial <transact-tx-data-in-transaction! db tx-data-or-fn))
report (<? (db/in-transaction! db in-transaction-fn))]
(when report
;; <r-t-t-d! returns non-nil or throws, but we still check report just in
;; case. Here, in-transaction! function completed and returned non-nil,
;; so the transaction has committed.
(reset! (:current-db conn) (:db-after report))
(>! (:listener-source conn) report))
report)))))]
;; Even when report is nil (transaction not committed), pair is non-nil.
(>! result pair))
(>! token-chan token)