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+# ResolveSpec - TODO List
+
+This document tracks incomplete features and improvements for the ResolveSpec project.
+
+## Core Features to Implement
+
+### 1. Column Selection and Filtering for Preloads
+**Location:** `pkg/resolvespec/handler.go:730`
+**Status:** Not Implemented
+**Description:** Currently, preloads are applied without any column selection or filtering. This feature would allow clients to:
+- Select specific columns for preloaded relationships
+- Apply filters to preloaded data
+- Reduce payload size and improve performance
+
+**Current Limitation:**
+```go
+// For now, we'll preload without conditions
+// TODO: Implement column selection and filtering for preloads
+// This requires a more sophisticated approach with callbacks or query builders
+query = query.Preload(relationFieldName)
+```
+
+**Required Implementation:**
+- Add support for column selection in preloaded relationships
+- Implement filtering conditions for preloaded data
+- Design a callback or query builder approach that works across different ORMs
+
+---
+
+### 2. Recursive JSON Cleaning
+**Location:** `pkg/restheadspec/handler.go:796`
+**Status:** Partially Implemented (Simplified)
+**Description:** The current `cleanJSON` function returns data as-is without recursively removing null and empty fields from nested structures.
+
+**Current Limitation:**
+```go
+// This is a simplified implementation
+// A full implementation would recursively clean nested structures
+// For now, we'll return the data as-is
+// TODO: Implement recursive cleaning
+return data
+```
+
+**Required Implementation:**
+- Recursively traverse nested structures (maps, slices, structs)
+- Remove null values
+- Remove empty objects and arrays
+- Handle edge cases (circular references, pointers, etc.)
+
+---
+
+### 3. Custom SQL Join Support
+**Location:** `pkg/restheadspec/headers.go:159`
+**Status:** Not Implemented
+**Description:** Support for custom SQL joins via the `X-Custom-SQL-Join` header is currently logged but not executed.
+
+**Current Limitation:**
+```go
+case strings.HasPrefix(normalizedKey, "x-custom-sql-join"):
+    // TODO: Implement custom SQL join
+    logger.Debug("Custom SQL join not yet implemented: %s", decodedValue)
+```
+
+**Required Implementation:**
+- Parse custom SQL join expressions from headers
+- Apply joins to the query builder
+- Ensure security (SQL injection prevention)
+- Support for different join types (INNER, LEFT, RIGHT, FULL)
+- Works across different database adapters (GORM, Bun)
+
+---
+
+### 4. Proper Condition Handling for Bun Preloads
+**Location:** `pkg/common/adapters/database/bun.go:202`
+**Status:** Partially Implemented
+**Description:** The Bun adapter's `Preload` method currently ignores conditions passed to it.
+
+**Current Limitation:**
+```go
+func (b *BunSelectQuery) Preload(relation string, conditions ...interface{}) common.SelectQuery {
+    // Bun uses Relation() method for preloading
+    // For now, we'll just pass the relation name without conditions
+    // TODO: Implement proper condition handling for Bun
+    b.query = b.query.Relation(relation)
+    return b
+}
+```
+
+**Required Implementation:**
+- Properly handle condition parameters in Bun's Relation() method
+- Support filtering on preloaded relationships
+- Ensure compatibility with GORM's condition syntax where possible
+- Test with various condition types
+
+---
+
+## Code Quality Improvements
+
+### 5. Modernize Go Type Declarations
+**Location:** `pkg/common/types.go:5, 42, 64, 79`
+**Status:** Pending
+**Priority:** Low
+**Description:** Replace legacy `interface{}` with modern `any` type alias (Go 1.18+).
+
+**Affected Lines:**
+- Line 5: Function parameter or return type
+- Line 42: Function parameter or return type
+- Line 64: Function parameter or return type
+- Line 79: Function parameter or return type
+
+**Benefits:**
+- More modern and idiomatic Go code
+- Better readability
+- Aligns with current Go best practices
+
+---
+
+## Additional Considerations
+
+### Documentation
+- Ensure all new features are documented in README.md
+- Update examples to showcase new functionality
+- Add migration notes if any breaking changes are introduced
+
+### Testing
+- Add unit tests for each new feature
+- Add integration tests for database adapter compatibility
+- Ensure backward compatibility is maintained
+
+### Performance
+- Profile preload performance with column selection and filtering
+- Optimize recursive JSON cleaning for large payloads
+- Benchmark custom SQL join performance
+
+---
+
+## Priority Ranking
+
+1. **High Priority**
+   - Column Selection and Filtering for Preloads (#1)
+   - Proper Condition Handling for Bun Preloads (#4)
+
+2. **Medium Priority**
+   - Custom SQL Join Support (#3)
+   - Recursive JSON Cleaning (#2)
+
+3. **Low Priority**
+   - Modernize Go Type Declarations (#5)
+
+---
+
+**Last Updated:** 2025-11-07