cljgae-template

A Leiningen template for creating Google App Engine apps in Clojure using the GAE Java SDK (supports 11 and 17 runtimes with bundled services)

Google App Engine is the first "Serverless" web PaaS the world has ever seen, launched as an opinionated, fully managed service 16 years ago. Designed to scale out-of-the-box, with many more features teams would take years to assemble. This temaplate is meant to get you started on appengine with Clojure quickly.

Release 1.0.3.1

Leiningen Clojars dependency:

[org.clojars.nickbauman/cljgae-template "1.0.3.1"]

Template Installation

To use this template locally, installing it into your library cache - ~/.m2/repository/.

From the root of the template project, run the following command:

lein install

Usage

lein new cljgae-template <project name> <project organization ID> <availability zone> <billing-account> <java-runtime>

Example:

lein new cljgae-template a4d07e6a3-f194-07d0-8a4b-1695 456350996759 us-central 4D2-1D73A5-012F81-6E5 17

Creates a new appengine project on disk under dir that should run on the Gen2 OSS Runtimes, (Java11/17 with bundled services). It has a few routes with corresponding tests which show the usage of a few appengine APIs such as

• Google Cloud Storage (via file upload test example)
• The datastore, including a Clojure DSL for querying the datastore (see db.clj test for examples)
• The App Identity Service API (via "/" route)
• Asyncronous task queues / AKA appengine"push queues" (via a JSON request of a "large" list of data points)
• User services with user state examples

With unit tests for each. All examples also run on the dev appserver.

Datastore query language

A Clojure DSL has been developed inspired by the Python NDB library (with an emphasis on Clojure's more functional idiom.) Queries return a lazy sequence.

Examples

(defentity BasicEntity [content saved-time repeated-value])

(defentity AnotherEntity [content saved-time int-value])

(let [entity (save! (create-AnotherEntity "Some content woo" (t/date-time 1980 3 5) 6))
      entity2 (save! (create-AnotherEntity "Other content" (t/date-time 1984 10 12) 91))
      entity3 (save! (create-AnotherEntity "More interesting content" (t/date-time 1984 10 12) 17))
                                        ; repeated properties
      root-entity (save! (create-BasicEntity "basic entity content" (t/date-time 2015 6 8) [1 2 3])) 
      child-entity1 (save! (create-AnotherEntity "child one content" (t/date-time 2016 12 10) 33) (gae-key root-entity))
      child-entity2 (save! (create-AnotherEntity "child two content" (t/date-time 2016 12 10) 44) (gae-key root-entity))]   
                                        ; query all
  (query-AnotherEntity [])
                                        ; equality
  (query-AnotherEntity [:content = "Some content woo"])
  (query-AnotherEntity [:content = "Blearg not found"])
                                        ; not equal
  (query-AnotherEntity [:content != "Not found"])
  (query-AnotherEntity [:content != "Other content"])
                                        ; greater-than and less-than
  (query-AnotherEntity [:int-value < 7])
  (query-AnotherEntity [:int-value < 5])
                                        ; time: before and after
  (query-AnotherEntity [:saved-time > (.toDate (t/date-time 1979 3 5))])
  (query-AnotherEntity [:saved-time < (.toDate (t/date-time 1979 3 5))])
                                        ; "and" compound queries
  (query-AnotherEntity [:and [:content = "Some content woo"] [:int-value > 5]])
  (query-AnotherEntity [:and [:int-value > 5] [:int-value <= 17]])
                                        ; "or" compound queries
  (query-AnotherEntity [:or [:content = "Some content woo"] [:int-value < 5]])
  (query-AnotherEntity [:or [:content = "Some content woo"] [:int-value > 5]])
                                        ; compound queries with nested compound predicates
  (query-AnotherEntity [:or [:content = "Other content"] 
                        [:and [:saved-time < (.toDate (t/date-time 1983 3 5))] [:int-value = 6]]])
                                        ; keys-only support
  (query-AnotherEntity [:int-value < 7] [:keys-only true])
                                        ; order-by support
  (query-AnotherEntity [:int-value > 0] [:order-by :int-value :desc])
                                        ; keys only and order-by support together 
  (query-AnotherEntity [:int-value > 0] [:keys-only true :order-by :int-value :desc])
                                        ; support multiple sort orders (with keys-only, too)
  (query-AnotherEntity [:saved-time > 0] [:order-by :saved-time :desc :int-value :asc :keys-only true])
                                        ; parents can find their children
  (query-AnotherEntity [] [:ancestor-key (gae-key root-entity)])
                                        ; ancestors that work with predicates
  (query-AnotherEntity [:int-value > 33] [:ancestor-key (gae-key root-entity)])
                                        ; ancestors that work with keys-only support
  (query-AnotherEntity [] [:keys-only true :ancestor-key (gae-key root-entity)])
  (query-AnotherEntity [] [:ancestor-key (gae-key root-entity) :keys-only true])
                                        ; ancestors that work with order-by
  (query-AnotherEntity [] [:ancestor-key (gae-key root-entity) :order-by :int-value :desc])
                                        ; transactions
  (with-transaction
     (save! (create-AnotherEntity "Content information" (t/date-time 1984 10 12) 201)))
                                        ; Cross-group transactions
  (with-xg-transaction
     (save! (create-AnotherEntity "Content information" (t/date-time 1984 10 12) 6001))
     (save! (create-AnotherEntity "More content information" (t/date-time 1984 10 12) 6002))))

Validation

Validation of datastore entity models is optional. Adding validation involves putting a vector of keys that match your model properties followed by a fully qualified function property. For example:

(ns gaeclj.example.valid
  (:require [gaeclj.ds :refer [defentity]]))

(defentity CostStrategy
           [uuid
            create-date
            cost-uuid
            strategy-description
            ordered-member-uuids
            ordered-percentages]
           [:uuid                 gaeclj.valid/valid-uuid?
            :create-date          gaeclj.valid/long?
            :cost-uuid            gaeclj.valid/valid-uuid?
            :strategy-description gaeclj.valid/string-or-nil?
            :ordered-member-uuids gaeclj.valid/repeated-uuid?
            :ordered-amounts      gaeclj.valid/repeated-longs?])

Creating a CostStrategy like this

(create-CostStrategy "8e5625f8-60ec-11ea-a1ec-a45e60d5bfab"
                                   (.getMillis (t/date-time 1999 12 31))
                                   (str (uuid/v1))
                                   "even distribution"
                                   [(str (uuid/v1)) (str (uuid/v1))]
                                   ["foo" "bar"]) ; not valid

... would cause a RuntimeException citing the two properties:

java.lang.RuntimeException: (create-CostStrategy ...) failed validation for props :ordered-amounts

Future directions

• Postgres dialect
• Add support for projections
• More comprehensive examples of task queues
• More comprehensive use of cloud storage
• Examples of other commonly used GAE apis

License

Copyright © 2016-2024 Nick Bauman and Peter Schwarz

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.