Katerina Sh ← All work
Case Study Integrations · Backend

Third-Party API Integrations

Integration services that transformed external data and APIs into reliable, application-ready workflows.

Integration layer boundary-isolated
External API
Files & feeds
Source-specific adapter
Validate · normalize · persist
Stable internal model
Role
Backend Developer
Project type
Private Commercial Experience · Anonymized Case Study
Tech stack
C#.NETREST APIsPostgreSQLSQLCSVScheduled JobsAutoMapper
01 — Delivered

What I delivered

  • Integrated external APIs into backend services
  • Implemented authentication and request handling for third-party systems
  • Normalized different external formats into stable internal models
  • Built scheduled data collection and synchronization workflows
  • Designed database structures for imported and historical data
  • Implemented CSV import and export utilities
  • Exposed normalized data to downstream services and user-facing tools
  • Handled errors, unavailable data, and provider-specific edge cases
02 — Overview

This work represents several commercial integrations where external APIs, files, and services had to be converted into reliable data for internal products, analytics workflows, and customer-facing features.

The main responsibility was not simply calling an external endpoint, but building the integration layer around it: authentication, mapping, validation, persistence, refresh logic, error handling, and clean internal contracts.

03 — Context

The problem

External systems rarely matched the application's internal data model or business workflow.

Different providers returned different structures, used different update schedules, and had different failure modes.

Raw responses could not be passed directly to product features or analytical services without validation, transformation, and storage.

04 — Approach

Solution

I built source-specific adapters that isolated external formats from the rest of the application.

Each integration handled provider communication and transformed incoming data into stable internal models. Scheduled processes refreshed data where required, while database-backed services supported historical access and reuse by downstream systems.

Bulk and offline workflows were supported through CSV import, export, and transformation utilities.

Adapter role isolation-first
Provider-specific formats & quirks at boundary
Source-specific adapter absorbs
Predictable internal contracts downstream
05 — Architecture

Integration flow

Provider-specific logic remained at the integration boundary, allowing the rest of the system to work with predictable internal contracts.

Pipeline
External API or file
Source-specific adapter
Validation & normalization
Internal data model
Database or downstream service
Application feature or analytical workflow
Refresh & reuse
Scheduled job
Persisted & historical data
Reused without re-fetching
06 — Features

Key features

Third-party API authentication

Request and response mapping

Data validation and normalization

Scheduled synchronization

Historical data storage

CSV import and export

Database loading workflows

Error and edge-case handling

Internal service contracts

Downstream API exposure

07 — Challenges

Technical challenges

The main challenge was absorbing inconsistency at the external boundary without spreading provider-specific assumptions through the application.

The integrations also needed to remain reliable when external data was incomplete, delayed, temporarily unavailable, or returned in formats that differed from internal expectations.

Another challenge was balancing refresh frequency, storage, and historical access without repeatedly requesting the same external data.

08 — Outcome

Outcome

The integration services turned external systems into stable internal capabilities that could be safely reused by products, reports, and analytical workflows.

This experience demonstrates the ability to connect third-party APIs to real business applications rather than treating integration as a simple request-and-response task.

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Katerina Sh · Full-Stack Engineer © 2026 Ninja Paws · All rights reserved