Add UUID support for parent_id columns in filament-tree

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This PR adds comprehensive UUID support for parent_id columns in filament-tree, addressing the limitation where the package only worked with integer parent IDs.

Problem

Previously, the package assumed integer parent_id values with -1 as the default for root nodes. This prevented users from using UUIDs in their tree schemas, as the package would:

1. Create integer columns in migrations via treeColumns()
2. Use numeric comparisons (<= 0) that don't work with UUIDs
3. Hard-code -1 as the default parent value
4. Fail to handle null parent values for UUID-based root nodes

Solution

The implementation adds UUID support while maintaining full backward compatibility:

Migration Support

Extended the treeColumns() macro to accept a parent column type parameter:

// Integer parent_id (existing behavior)
$table->treeColumns();

// UUID parent_id (new)
$table->treeColumns('string', 'uuid');

// String parent_id (new)  
$table->treeColumns('string', 'string');

Configuration Flexibility

Users can now configure the default parent ID to work with UUIDs:

// For UUID trees
'default_parent_id' => null,

// For integer trees (existing)
'default_parent_id' => -1,

Smart Logic

Updated comparison and tree-building logic to handle both numeric and non-numeric parent keys:

• Root node detection works with both -1 (integers) and null (UUIDs)
• Tree building logic distinguishes between numeric and string comparisons
• Model methods like isRoot() and scopeIsRoot() handle both cases with proper SQL generation

Example Usage

// Model with UUID support
class Category extends Model
{
    use HasUuids, ModelTree;
    
    protected $fillable = ['parent_id', 'title', 'order'];
    protected $casts = ['parent_id' => 'string'];
}

// Data structure
[
    ['id' => 'uuid-1', 'parent_id' => null, 'title' => 'Root'],
    ['id' => 'uuid-2', 'parent_id' => 'uuid-1', 'title' => 'Child'],
]

Code Quality Improvements

During implementation review, several logic issues were identified and fixed:

• Fixed SQL query generation for UUID root detection (WHERE parent_id IS NULL vs WHERE parent_id = NULL)
• Standardized to strict type comparisons throughout the codebase
• Added input validation for migration parameters
• Enhanced documentation with clear configuration requirements

All existing integer-based implementations continue to work without any changes required.

Fixes #83.

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[lam0819]

@copilot review first before i review

[Copilot]

@copilot review first before i review

I've completed my review of the UUID support implementation and identified several logic issues that I've now fixed:

Issues Found & Fixed:

1. SQL Query Logic Error: scopeIsRoot() was using WHERE parent_id = NULL which never matches records. Fixed to use WHERE parent_id IS NULL for UUID keys.

2. Inconsistent Comparisons: Mixed strict (===) and loose (==) comparisons. Standardized to strict comparisons throughout.

3. Array Key Issues: selectArray() method tried to use null as array key for UUID scenarios. Added guard logic to only include root option for integer keys.

4. Input Validation: Added validation for treeColumns() parent type parameter to prevent invalid values.

5. Logic Cleanup: Removed unreachable conditions in tree building logic and improved null handling.

6. Documentation: Enhanced README with clearer configuration requirements and troubleshooting guidance.

The implementation now properly handles both integer and UUID parent keys with correct SQL generation and type-safe comparisons. All backward compatibility is maintained for existing integer-based trees.

Commit: bd153ef

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