Initial commit: Material Texture API service

- Go + Gin + GORM + PostgreSQL backend
- RESTful API for material management
- Docker deployment support
- Database partitioning for billion-scale data
- API documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/repository/binding.go

@@ -0,0 +1,104 @@
+package repository
+
+import (
+	"material_texture/internal/models"
+
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+type BindingRepository struct {
+	db *gorm.DB
+}
+
+func NewBindingRepository(db *gorm.DB) *BindingRepository {
+	return &BindingRepository{db: db}
+}
+
+// BindMaterial 绑定材质到多个group_id（幂等操作，使用upsert）
+// 优化: 分批处理，避免单条 SQL 过大
+func (r *BindingRepository) BindMaterial(materialID int64, groupIDs []string) error {
+	const batchSize = 1000 // 每批最多 1000 条
+
+	for i := 0; i < len(groupIDs); i += batchSize {
+		end := i + batchSize
+		if end > len(groupIDs) {
+			end = len(groupIDs)
+		}
+
+		batch := groupIDs[i:end]
+		bindings := make([]models.MaterialBinding, len(batch))
+		for j, groupID := range batch {
+			bindings[j] = models.MaterialBinding{
+				MaterialID: materialID,
+				GroupID:    groupID,
+			}
+		}
+
+		// 使用 ON CONFLICT DO NOTHING 实现幂等
+		if err := r.db.Clauses(clause.OnConflict{
+			Columns:   []clause.Column{{Name: "material_id"}, {Name: "group_id"}},
+			DoNothing: true,
+		}).Create(&bindings).Error; err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// UnbindMaterial 解绑材质与指定的group_id
+func (r *BindingRepository) UnbindMaterial(materialID int64, groupIDs []string) error {
+	return r.db.Where("material_id = ? AND group_id IN ?", materialID, groupIDs).
+		Delete(&models.MaterialBinding{}).Error
+}
+
+// GetGroupsByMaterialID 根据材质ID获取所有关联的group_id (分页版本)
+func (r *BindingRepository) GetGroupsByMaterialID(materialID int64, page, pageSize int) ([]string, int64, error) {
+	var groupIDs []string
+	var total int64
+
+	db := r.db.Model(&models.MaterialBinding{}).Where("material_id = ?", materialID)
+
+	// 获取总数
+	if err := db.Count(&total).Error; err != nil {
+		return nil, 0, err
+	}
+
+	// 分页查询
+	offset := (page - 1) * pageSize
+	err := db.Order("created_at DESC").
+		Offset(offset).
+		Limit(pageSize).
+		Pluck("group_id", &groupIDs).Error
+
+	return groupIDs, total, err
+}
+
+// GetMaterialsByGroupIDs 根据多个group_id获取关联的材质（含材质详情）
+func (r *BindingRepository) GetMaterialsByGroupIDs(groupIDs []string) ([]models.GroupMaterialResult, error) {
+	var bindings []models.MaterialBinding
+
+	err := r.db.Preload("Material").
+		Where("group_id IN ?", groupIDs).
+		Find(&bindings).Error
+	if err != nil {
+		return nil, err
+	}
+
+	results := make([]models.GroupMaterialResult, len(bindings))
+	for i, binding := range bindings {
+		results[i] = models.GroupMaterialResult{
+			GroupID:  binding.GroupID,
+			Material: binding.Material,
+		}
+	}
+
+	return results, nil
+}
+
+// DeleteByMaterialID 删除材质的所有绑定（材质删除时级联调用）
+func (r *BindingRepository) DeleteByMaterialID(materialID int64) error {
+	return r.db.Where("material_id = ?", materialID).
+		Delete(&models.MaterialBinding{}).Error
+}