eventsourcing/es4j

Problem: Min/Max queries are global to the attribute

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#209 opened on Jan 27, 2017

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 (0 comments) (0 reactions) (0 assignees)Java (406 stars) (27 forks)batch import
enhancementhelp wanted

Description

At this moment, Min/Max queries are limited to finding the smallest or largest value of a particular attribute globally across an entity. Which means you can tell "what's the latest order" but not "what's the latest order for this person". IsLatestEntity/LatestAssociatedEntryQuery are currently being used to address this type of need, but they are very slow and cumbersome. Min/Max has been already optimized for PostgreSQL storage.

It would have been great if it was possible to fit this type query within Min/Max as an option:

// Find the last order for user with id=<id>
max(Order.TIMESTAMP, equal(Order.USER_ID, id))
// Find all last orders for all users
max(Order.TIMESTAMP, Order.USER_ID)

(Or something similar)

Contributor guide

Tech stack
javapostgresql
Domain
backenddatabaseapi
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
JavaEvent sourcing basicses4j query API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The issue proposes adding filtering and grouping to the Min/Max query functions. To implement, study the existing Min/Max implementation in the es4j framework, likely in files related to query building and execution. The examples given in the issue show the desired API, and the current IsLatestEntity/LatestAssociatedEntryQuery are slow alternatives. The implementation should extend the Min/Max classes to accept optional filter and groupBy parameters, and ensure PostgreSQL optimization is maintained.