projection-patterns

Build read models and projections from event streams. Use when implementing CQRS read sides, building materialized views, or optimizing query performance in event-sourced systems.

Install with Tessl CLI

npx tessl i github:wshobson/agents --skill projection-patterns

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Overall
score

78%

Review — 78%

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Evaluation — 95%

↑ 1.73x

Agent success when using this skill

Validation — 13 / 16 Passed

Validation for skill structure

SKILL.md

Review

Evals

Evaluation results

100%

62%

Library Checkout Read Model

Core projection class structure

Criteria

Without context

With context

Event dataclass

100%

stream_id field

100%

global_position field

100%

version field

100%

Projection ABC

100%

Abstract name property

100%

Abstract handles method

100%

Abstract apply method

100%

asyncpg Pool usage

100%

Pool acquire pattern

100%

Handler dispatch dict

60%

100%

Denormalized table

100%

Three event types handled

57%

100%

Separate handler methods

100%

Without context: $0.3068 · 1m 35s · 13 turns · 13 in / 5,017 out tokens

With context: $0.5818 · 2m 9s · 20 turns · 19 in / 7,856 out tokens

100%

47%

Resilient Event Projection Runner

Projector checkpointing and rebuild

Criteria

Without context

With context

Projector constructor

100%

Projections list

100%

Polling interval

100%

Default batch size 100

33%

100%

Rebuild batch size 1000

100%

Checkpoint default to 0

100%

Checkpoint save per event

100%

Saves global_position

100%

Rebuild deletes checkpoint

100%

Rebuild uses projection name

100%

Handles unregistered types

63%

100%

Without context: $0.3146 · 1m 20s · 14 turns · 63 in / 4,733 out tokens

With context: $0.5413 · 1m 50s · 21 turns · 259 in / 6,604 out tokens

84%

11%

SaaS Usage Analytics Projections

Aggregating upserts and multi-table transactions

Criteria

Without context

With context

ON CONFLICT upsert

100%

Incremental counter update

100%

Transaction for multi-table

67%

100%

Both tables in transaction

100%

asyncpg Pool pattern

100%

Idempotent daily upsert

100%

Handler dispatch dict

Error handling present

13%

Date extraction for daily key

100%

Separate projection classes

100%

Implementation notes file

100%

Without context: $0.3420 · 1m 38s · 12 turns · 12 in / 6,381 out tokens

With context: $0.3893 · 1m 44s · 15 turns · 303 in / 5,032 out tokens

Evaluated: about 4 hours ago
Agent: Claude Code

Table of Contents

Library Checkout Read Model Resilient Event Projection Runner SaaS Usage Analytics Projections

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