api: migrate Transaction model/service to Decimal

[zensgit]

Scope: Transaction model amount fields and TransactionService balances to Decimal. Validation: SQLx prepare, Clippy strict, tests all pass locally. No DB schema change (transactions.amount is DECIMAL).

[gemini-code-assist]

Summary of Changes

Hello @zensgit, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request migrates the Transaction model and TransactionService to use the Decimal type for all amount-related fields and balance calculations. This change is crucial for maintaining accuracy in financial operations by avoiding the inherent precision issues of floating-point numbers, without requiring any database schema modifications.

Highlights

• Data Type Migration: Changed amount fields in Transaction, TransactionCreate, and TransactionUpdate structs from f64 to rust_decimal::Decimal to prevent floating-point inaccuracies in financial calculations.
• Service Logic Update: Updated TransactionService methods to use Decimal for handling account balances, ensuring consistent precision across the API.

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[Copilot]

Pull Request Overview

This PR migrates the Transaction model and TransactionService from using f64 to rust_decimal::Decimal for monetary amounts. This change improves financial calculation precision by avoiding floating-point arithmetic issues common with monetary values.

• Transaction model amount fields changed from f64 to Decimal
• TransactionService balance queries updated to use Decimal type
• Added rust_decimal::Decimal import to both files

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
jive-api/src/models/transaction.rs	Updated Transaction, TransactionCreate, and TransactionUpdate structs to use Decimal for amount fields
jive-api/src/services/transaction_service.rs	Updated balance queries and HashMap type annotations to use Decimal instead of f64

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[gemini-code-assist]

Code Review

This is a valuable change to migrate monetary values from f64 to Decimal, which is essential for financial accuracy. The modifications to the Transaction model are correct. However, the migration is incomplete in TransactionService, where some functions and structs still use f64. I've added a comment on the new Decimal import to highlight these areas that need to be updated to ensure consistency and prevent potential bugs. Completing this migration will solidify the correctness of the financial calculations.

[gemini-code-assist]

While Decimal has been correctly introduced for many parts of the service, the migration is incomplete in this file. There are still functions using f64 for monetary values, which could lead to precision errors and runtime bugs.

To complete the migration, please update the following:

1. auto_categorize function: The transaction amount is still fetched as an f64 around line 284. This should be Decimal.

   // Around line 284
   let transaction: Option<(String, Option<String>, f64)> =
       sqlx::query_as(...)

   This should be changed to:

   let transaction: Option<(String, Option<String>, Decimal)> =
       sqlx::query_as(...)

2. TransactionStatistics struct: This struct (around line 383) and its usage in get_statistics still rely on f64. All monetary fields should be Decimal.

   // Around line 383
   pub struct TransactionStatistics {
       pub total_income: Option<f64>,
       pub total_expense: Option<f64>,
       pub net_amount: Option<f64>,
       pub avg_expense: Option<f64>,
       pub max_expense: Option<f64>,
       // ...
   }

   This should be updated to use Option<Decimal> for all monetary fields.

Ensuring Decimal is used consistently is critical for the correctness of financial calculations.