---
phase: 09-time-dimensions
plan: 01
subsystem: model
tags: [rust, serde, time-dimensions, validation]

requires:
  - phase: 08-cpp-shim-infrastructure
    provides: nothing directly (structural prerequisite)

provides:
  - Dimension struct with dim_type and granularity optional fields
  - Time dimension validation in SemanticViewDefinition::from_json
  - Default derive on Dimension for ergonomic struct construction

affects: [09-02, expand.rs, table_function.rs]

tech-stack:
  added: []
  patterns:
    - "#[serde(default, rename = 'type')] for Rust keyword field names"
    - "Post-deserialization validation in from_json returning Result<Self, String>"

key-files:
  created: []
  modified:
    - src/model.rs
    - src/expand.rs

key-decisions:
  - "Used dim_type as field name with #[serde(rename = 'type')] — type is a Rust keyword"
  - "Added Default derive to Dimension to simplify struct construction in tests"
  - "Validation in from_json after deserialization catches: unknown type, missing granularity, unsupported granularity"
  - "Updated all Dimension struct literals in expand.rs tests with new fields (source_table: Some(...) cases needed manual Python script)"

patterns-established:
  - "Pattern: serde(rename) for Rust keyword field names — apply to any future reserved-word JSON keys"
  - "Pattern: post-deserialization validation in from_json — add validation loops after serde parse"

requirements-completed: [TIME-01]

duration: 25min
completed: 2026-03-01
---

# Phase 9 Plan 01 Summary

**Extended Dimension struct with time-typed fields and define-time validation for time dimension declarations.**

## Performance

- **Duration:** ~25 min
- **Started:** 2026-03-01T00:00:00Z
- **Completed:** 2026-03-01T00:00:00Z
- **Tasks:** 1 (TDD cycle: RED → GREEN → refactor for Dimension struct expansion)
- **Files modified:** 2

## Accomplishments

- `Dimension` struct now has `dim_type: Option<String>` (serde rename `"type"`) and `granularity: Option<String>` — both `#[serde(default)]` for backward compat
- `SemanticViewDefinition::from_json` validates: unknown dim type, missing granularity for time dims, unsupported granularity values
- 6 new tests in `time_dimension_tests` module — all pass
- 60 total lib tests pass — no regressions

## Task Commits

1. **Task 1: Add dim_type + granularity fields to Dimension and validation to from_json** - `558799e` (feat)

## Files Created/Modified

- `src/model.rs` - Added dim_type + granularity to Dimension struct; updated from_json with validation; added 6 new tests
- `src/expand.rs` - Updated all Dimension struct literals to include new fields (no behavior change)

## Self-Check: PASSED

- [x] `cargo test --lib` passes: 60/60 tests
- [x] `dim_type: Option<String>` field present with `#[serde(rename = "type")]`
- [x] `granularity: Option<String>` field present with `#[serde(default)]`
- [x] `from_json` validates time dimensions with descriptive error messages
- [x] All 6 new tests pass
- [x] Backward compat: existing JSON without type/granularity fields deserializes correctly
