我在编写我认为可重用的一般数据查询时遇到了麻烦。
例如，从这篇文章跟进，是否有一种规范的方法可以从特定的 datomic 分区中获取所有标识？，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。
该函数显示“: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接受输入的函数时，我必须在各处加上引号才能使其工作。
(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？
- - - 更新 - - - -
供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*))