https://github.com/brabster/dynamodb-expressions

Better DynamoDB expressions with Clojure
https://github.com/brabster/dynamodb-expressions

Last synced: 1 day ago
JSON representation

Better DynamoDB expressions with Clojure

• Host: GitHub
• URL: https://github.com/brabster/dynamodb-expressions
• Owner: brabster
• License: epl-1.0
• Created: 2016-11-27T20:09:42.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2017-07-23T09:24:21.000Z (over 7 years ago)
• Last Synced: 2024-10-28T13:25:30.877Z (20 days ago)
• Language: Clojure
• Size: 46.9 KB
• Stars: 6
• Watchers: 2
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.org
  • License: LICENSE

Awesome Lists containing this project

README

        
* dynamodb-expressions

[[https://travis-ci.org/brabster/dynamodb-expressions][https://img.shields.io/travis/brabster/dynamodb-expressions.svg]]

[[https://github.com/brabster/dynamodb-expressions/releases/latest][https://img.shields.io/github/release/brabster/dynamodb-expressions.svg]]

[[http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.Modifying.html][DynamoDB Update Expressions]] in Clojure, designed for use with [[https://github.com/mcohen01/amazonica][Amazonica]].

Get the latest version on [[https://clojars.org/dynamodb-expressions][Clojars]]

* Why?

DynamoDB's native update expression syntax requires placeholders be

specified for all values and, under some circumstances, for names

too. That typically means (in my experience, anyway) verbose, brittle

and hard-to-read code.

The nested-map structure also makes these values hard to manipulate in

a threading-friendly way.

Contrived, worst-case example: we want to update a customer document,

primary key "customer-id", adding 1 to the ~auth-attempts~ key, and

setting the nested ~call.at~ key to "today".

Because ~auth-attempts~ includes a hyphen, and both ~call~ and ~at~

are DynamoDB reserved words, we must set name placeholders for

them. We might write something like this:

#+BEGIN_SRC clojure

{:key {:customer-id "foo"}

 :update-expression "ADD #auth_attempts :auth_attempts_val SET #call.#at = :call_at_value"

 :expression-attribute-names {"#auth_attempts" "auth-attempts"

                              "#call" "call"

                              "#at" "at"}

 :expression-attribute-values {":auth_attempts_val" 1

                               ":call_at_value" "today"}}

#+END_SRC

I don't think that expresses what I'm trying to do very clearly. This

library allows you to write instead:

#+BEGIN_SRC clojure

(require '[dynamodb-expression.core :as dx])

(->

  (dx/update-expr {:customer-id "foo"})

  (dx/add :auth-attempts 1)

  (dx/set [:call :at] "today")

  dx/expr)

#+END_SRC

Which produces something like the following, applying placeholders for

all names. Some indication of where the placeholder came from is

retained to help debugging:

#+BEGIN_SRC clojure

{:update-expression

 "ADD #nauth_attempts_21478 :vauth_attempts_21478 SET #ncall_21479.#ncall_at_21480 = :vcall_at_21480"

 :key {:customer-id "foo"}

 :expression-attribute-names {"#nauth_attempts_21478" "auth-attempts"

                              "#ncall_at_21480" "at"

                              "#ncall_21479" "call"},

 :expression-attribute-values {":vauth_attempts_21478" 1

                               ":vcall_at_21480" "today"}}

#+END_SRC

* Unsupported Functionality

The following update expression features are not supported

(yet!). Raise an issue and/or submit a PR if you need these.

** array syntax

There's no way to access array elements right now.

** functions

Nor can you use functions like ~list_append~.

* dynamodb Grammar

To test condition expressions without nasty string hacking, there's a

grammar for condition expressions, based on the documentation.

* License

Copyright © 2016 Paul Brabban

Distributed under the Eclipse Public License either version 1.0 or (at

your option) any later version.