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Archive for the ‘datomic’ Category

annotate Datomic transaction to record side effect

Posted by eggsearle on October 13, 2013

Extends previous post to indicate how the transaction can be annotated to indicate the email was generated.

In the general form, this can capture any metadata required to describe process(es) that have been executed, decisions made, etc.

 

 

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Datomic txReport and tracking changes via Datomisca queries

Posted by eggsearle on October 13, 2013

A common web site use case is notifying a user of a change of address, with notifications to both old and new addresses.
This is a simple mechanism that helps to address fraud.

Generally this code would form part of the http post action, perhaps including some indirection via a queue.
Arguably that logic is orthogonal to the primary function of the web site.

Datomic records all changes to entities and provides a notification mechanism

The following gist illustrates how this might be implemented.

Line 39 creates a user with the name “john” and email “jon@example.com”.
Line 44 updates that user, changing the email to “john@example.net”

Line 46 defines a query that will retrieve the name and previous email, given a delta to the user entity

Line 59 will print empty result since qe is the change that created the user (and there is thus no previous value)
Line 62 creates the result:(“john”, “jon@example.com”,”john@example.net”)
Which provides the name, before and after emails needed to send the warning email.

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