我在编写我认为可重用的一般数据组查询时遇到问题.
例如,从这篇文章接下来有一个规范的方法来从特定的数据组分区中获取所有的ident？,我安装了以下架构
{[63 :account/password]
[64 :account/firstName]
[65 :account/lastName]
[62 :account/username]
[69 :email/prority]
[68 :email/address]}
我想要一个只显示具有给定命名空间的属性的函数.
此函数显示":account"命名空间中的所有属性
(d/q '[:find ?e ?ident :where
[?e :db/ident ?ident]
[_ :db.install/attribute ?e]
[(.toString ?ident) ?val]
[(.startsWith ?val ":account")]] (d/db *conn*))
;; => [62 :account/username] [63 :account/password]
;; [64 :account/firstName] [65 :account/lastName]
但是,当我想编写一个可以输入的函数时,我必须在任何地方放置引号以使其工作.
(defn get-ns-attrs [?ns db]
(d/q [':find '?e '?ident ':where
['?e ':db/ident '?ident]
['_ ':db.install/attribute '?e]
[(list '.toString '?ident) '?val]
[(list '.startsWith '?val (str ":" ?ns))]] db))
(get-ns-attrs "account" (d/db *conn*))
;; => [62 :account/username] [63 :account/password]
;; [64 :account/firstName] [65 :account/lastName]
(get-ns-attrs "email" (d/db *conn*))
;; => [69 :email/prority] [68 :email/address]
有一个更好的方法吗？
人们尝试的完整代码在这里:
(ns schema.start
(:require [datomic.api :as d])
(:use [clojure.pprint :only [pprint]]))
(def *uri* "datomic:mem://login-profile")
(d/create-database *uri*)
(def *conn* (d/connect *uri*))
(defn boolean? [x]
(instance? java.lang.Boolean x))
(defn db-pair [attr kns val f]
(list (keyword (str "db/" (name attr)))
(f val kns)))
(defn db-enum [val kns]
(keyword (str "db." (name kns) "/" (name val))))
(def DB-KNS
{:ident {:required true
:check keyword?}
:type {:required true
:check #{:keyword :string :boolean :long :bigint :float
:double :bigdec :ref :instant :uuid :uri :bytes}
:attr :valueType
:fn db-enum}
:cardinality {:required true
:check #{:one :many}
:fn db-enum}
:unique {:check #{:value :identity}
:fn db-enum}
:doc {:check string?}
:index {:check boolean?}
:fulltext {:check boolean?}
:component? {:check keyword?}
:no-history {:check boolean?}})
(defn process-kns [m kns params res]
(let [val (m kns)]
(cond (nil? val)
(if (:required params)
(throw (Exception. (str "key " kns " is a required key")))
res)
:else
(let [chk (or (:check params) (constantly true))
f (or (:fn params) (fn [x & xs] x))
attr (or (:attr params) kns)]
(if (chk val)
(apply assoc res (db-pair attr kns val f))
(throw (Exception. (str "value " val " failed check"))))))))
(defn schema [m]
(loop [db-kns# DB-KNS
output {}]
(if-let [entry (first db-kns#)]
(recur (rest db-kns#)
(process-kns m (first entry) (second entry) output))
(assoc output
:db.install/_attribute :db.part/db
:db/id (d/tempid :db.part/db)))))
(def account-schema
[(schema {:ident :account/username
:type :string
:cardinality :one
:unique :value
:doc "The username associated with the account"})
(schema {:ident :account/password
:type :string
:cardinality :one
:doc "The password associated with the account"})
(schema {:ident :account/firstName
:type :string
:cardinality :one
:doc "The first name of the user"})
(schema {:ident :account/lastName
:type :string
:cardinality :one
:doc "The first name of the user"})
(schema {:ident :account/otherEmails
:type :ref
:cardinality :many
:doc "Other email address of the user"})
(schema {:ident :account/primaryEmail
:type :ref
:cardinality :one
:doc "The primary email address of the user"})])
(def email-schema
[(schema {:ident :email/address
:type :string
:cardinality :one
:unique :value
:doc "An email address"})
(schema {:ident :email/priority
:type :long
:cardinality :one
:doc "An email address's priority"})])
(d/transact *conn* account-schema)
(d/transact *conn* email-schema)
(defn get-ns-attrs1 [?ns db]
(d/q [':find '?e '?ident ':where
['?e ':db/ident '?ident]
['_ ':db.install/attribute '?e]
[(list '.toString '?ident) '?val]
[(list '.startsWith '?val (str ":" ?ns))]] db))
(defn get-ns-attrs2 [?ns db]
(d/q '[:find ?e ?ident :where
[?e :db/ident ?ident]
[_ :db.install/attribute ?e]
[(.toString ?ident) ?val]
[(.startsWith ?val ~(str ":" ?ns))]] db))
(get-ns-attrs1 "account" (d/db *conn*))
(get-ns-attrs1 "email" (d/db *conn*))
(get-ns-attrs2 "account" (d/db *conn*))
(get-ns-attrs2 "email" (d/db *conn*))
经过多一点阅读后,我发现:in关键字是所有这一切的关键.示例在教程的"高级查询"部分中给出 - http://docs.datomic.com/tutorial.html.
这是列出:account命名空间中所有属性的等效查询
(d/q '[:find ?e ?ident ?ns :in $ ?ns :where
[?e :db/ident ?ident]
[_ :db.install/attribute ?e]
[(.toString ?ident) ?val]
[(.startsWith ?val ?ns)]]
(d/db *conn*)
"account")
;; => #<HashSet [[68 :account/firstName], [67 :account/password], [71 :account/primaryEmail], [66 :account/username], [69 :account/lastName], [70 :account/otherEmails]]>
这是函数中的等价物
(defn get-ns-attrs [_ns db]
(d/q '[:find ?e ?ident :in $ ?ns :where
[?e :db/ident ?ident]
[_ :db.install/attribute ?e]
[(.toString ?ident) ?val]
[(.startsWith ?val ?ns) ]] db (str _ns)))
(get-ns-attrs :account (d/db *conn*))
;; => #<HashSet [[68 :account/firstName], [67 :account/password], [71 :account/primaryEmail], [66 :account/username], [69 :account/lastName], [70 :account/otherEmails]]>
如果您需要更多模块化,可以使用%传递一组规则来进一步细分该功能:
(def rule-nsAttrs
'[[nsAttrs ?e ?ident ?ns]
[?e :db/ident ?ident]
[_ :db.install/attribute ?e]
[(.toString ?ident) ?val]
[(.startsWith ?val ?ns)]])
(defn get-ns-attrs [_ns db]
(d/q '[:find ?e ?ident :in $ % ?ns :where
(nsAttrs ?e ?ident ?ns)]
(d/db *conn*)
[rule-nsAttrs]
(str _ns)))
(get-ns-attrs :account (d/db *conn*))
;; => #<HashSet [[68 :account/firstName], [67 :account/password], [71 :account/primaryEmail], [66 :account/username], [69 :account/lastName], [70 :account/otherEmails]]>
可以使用Clojure的命名空间更简单地解决：
(d/q '[:find ?name :in $ ?ns
:where [_ :db.install/attribute ?a]
[?a :db/ident ?name]
[(namespace ?name) ?attr-ns]
[(= ?attr-ns ?ns)]] (d/db *conn*) "account")
返回：
#{[:account/password]
[:account/firstName]
[:account/lastName]
[:account/username]}