271 lines
8.6 KiB
Markdown
271 lines
8.6 KiB
Markdown
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---
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tags: [GORM, Go, ORM, 软删除, SoftDelete, Unscoped, DeletedAt]
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create time: 2026-04-28 00:00
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---
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# 软删除
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## 概述
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软删除是一种「逻辑删除」策略——数据并没有真正消失，只是被标记为「已删除」。这是 Web 应用中处理「删除」操作的**默认推荐方式**，因为它提供了可恢复性和审计追踪能力。
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```mermaid
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flowchart TD
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A[调用 db.Delete(&user)] --> SoftDel{"模型有<br/>DeletedAt 字段?"}
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SoftDel --> |否| HardSQL["DELETE FROM users WHERE id = ?<br/>⚠️ 物理删除，不可恢复"]
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SoftDel --> |是| UpdateSQL["UPDATE users SET deleted_at = NOW() WHERE id = ?<br/>✅ 软删除，数据保留"]
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UpdateSQL --> Query{常规查询?}
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Query --> |是| Filtered["WHERE deleted_at IS NULL<br/>已删除记录自动隐藏"]
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Query --> |否| UnscopedQ{需要已删除数据?}
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UnscopedQ --> |是| IncludeAll["Unscoped() → 全部返回"]
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UnscopedQ --> |否| Filtered
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style Start fill:#4FC08D,color:#fff
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style Filtered fill:#3B82F6,color:#fff
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style HardSQL fill:#EF4444,color:#fff
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```
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## DeletedAt 机制
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### 声明式启用
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在 struct 中嵌入 `gorm.Model` 或显式声明 `DeletedAt gorm.DeletedAt`：
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```go
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type User struct {
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gorm.Model // 自动包含 ID, CreatedAt, UpdatedAt, DeletedAt
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Name string `gorm:"size:64;not null"`
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}
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// 等价的手动声明
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type Product struct {
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ID uint `gorm:"primaryKey"`
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Name string `gorm:"size:128;not null"`
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Price float64 `gorm:"not null"`
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CreatedAt time.Time
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UpdatedAt time.Time
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DeletedAt gorm.DeletedAt // 软删除字段
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}
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```
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> [!note] gorm.DeletedAt 的本质
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> `gorm.DeletedAt` 是 `time.Time` 的类型别名，但它告诉 GORM 这是一个软删除标记。只有当这个字段存在时，GORM 才会开启软删除行为。
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### 软删除 vs 物理删除
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```go
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var user User
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// ===== 软删除（推荐）=====
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db.Delete(&user) // UPDATE users SET deleted_at=... WHERE id=?
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// 查询时自动过滤：SELECT * FROM users WHERE deleted_at IS NULL AND id=?
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// ===== 物理删除 =====
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db.Unscoped().Delete(&user) // DELETE FROM users WHERE id=?
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// 彻底擦除，无法恢复！
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// ===== 根据条件批量物理删除 =====
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db.Unscoped().Where("deleted_at < ?", time.Now().AddDate(-90, 0, 0)).Delete(&User{})
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// 清理超过 90 天未激活的软删除记录
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```
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## 查询已删除数据
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### Unscoped — 忽略软删除过滤
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`Unscoped()` 会关闭 GORM 自动附加的 `deleted_at IS NULL` 条件，让所有查询都能看到已删除的数据：
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```go
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// 查询所有用户（包括已删除的）
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var allUsers []User
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db.Unscoped().Find(&allUsers)
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// SELECT * FROM users; -- 不再附加 deleted_at 条件
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// 查找特定已删除的用户
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var deletedUser User
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db.Unscoped().Where("id = ? AND deleted_at IS NOT NULL", 42).First(&deletedUser)
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// 统计已删除的记录数
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var count int64
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db.Model(&User{}).Unscoped().Where("deleted_at IS NOT NULL").Count(&count)
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```
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### 精确查询含/不含已删除数据
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```go
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// 只查正常用户
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db.Where("deleted_at IS NULL").Find(&users)
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// 只查已删除用户
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db.Where("deleted_at IS NOT NULL").Find(&deletedUsers)
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```
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> [!tip] 为什么不用 Where + Unscoped？
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> `Unscoped()` 是一个全局开关，一旦开启就影响当前链的所有后续操作：
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> ```go
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> // ❌ 意外行为 —— Unscoped 后面的 Find 也不过滤
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> db.Where("name = 'john'").Unscoped().Find(&users)
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> // SELECT * FROM users WHERE name = 'john'; -- 包括已删除的 john！
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>
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> // ✅ 精确控制
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> db.Where("name = ? AND deleted_at IS NULL", "john").Find(&users)
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> ```
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## 软删除中的关联处理
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### HasMany / BelongsTo
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软删除模型的关联查询默认也会过滤已删除的关联项：
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```go
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type User struct {
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gorm.Model
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Name string
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Orders []Order `gorm:"foreignKey:UserID"`
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}
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type Order struct {
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gorm.Model
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UserID uint
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}
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var user User
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db.Preload("Orders").First(&user, 1)
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// Preload 生成的 SQL 会自动加入 deleted_at IS NULL：
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// SELECT * FROM orders WHERE user_id = 1 AND deleted_at IS NULL;
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```
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### ManyToMany
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对于多对多关联，GORM 在操作中间表时也会考虑软删除状态：
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```go
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// 给订单添加商品（如果商品已被软删除，默认不会关联）
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product := Product{Name: "Go Programming"}
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db.Model(&order).Association("Products").Append(&product)
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// 如果要强制关联已删除的商品
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db.Model(&order).Clauses(clause.OnConflict{DoNothing: true}).
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Association("Products").Append(&product)
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```
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> [!question] 思考题
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> 如果一个父记录被软删除，它的子记录（HasMany）还能被查询到吗？
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>
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> > **答案**：取决于查询起点。以未删除的父记录查询，子记录的软删除仍然生效；但如果你先 Unscoped 查到了已删除的父记录，再 Preload 其关联，子记录的软删除状态由 Preload 决定。
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## 唯一约束与软删除冲突
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这是软删除最常见的坑点——唯一约束检查在 UPDATE 之前执行，而旧记录仍然占着唯一值：
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```go
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type Article struct {
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gorm.Model
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Slug string `gorm:"uniqueIndex;not null"` // 例如：my-first-post
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}
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// 第一次保存成功
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db.Create(&Article{Slug: "my-first-post"})
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// 更新 slug
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db.Model(&Article{}).Where("id = ?", 1).Update("slug", "my-updated-post")
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// UPDATE articles SET slug='my-updated-post', deleted_at=NULL WHERE id=1;
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// ⚠️ MySQL 不会对已删除行检查唯一约束（InnoDB bug）
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// ⚠️ PostgreSQL 和 SQLite 会报错：duplicate key value
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```
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### 解决方案
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```go
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// 方案一：使用部分唯一索引（PostgreSQL 支持）
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// CREATE UNIQUE INDEX idx_articles_slug ON articles(slug) WHERE deleted_at IS NULL;
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// GORM 暂不直接支持部分索引，需手动执行 SQL
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// 方案二：额外加一个版本字段
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type Article struct {
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gorm.Model
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Slug string `gorm:"not null"`
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SlugHash string `gorm:"uniqueIndex;not null"` // slug + 随机哈希
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}
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// 方案三：用复合唯一索引覆盖软删除标记
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// 在数据库层面创建 (slug, is_deleted) 联合唯一约束
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```
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> [!warning] 跨数据库行为不一致
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> MySQL 的 InnoDB 引擎在处理软删除行的唯一约束时存在历史缺陷，不同版本行为可能不同。**不要依赖这种行为一致性**，应在应用层做好校验。
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## 恢复已删除数据
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```go
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// 恢复单个记录
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db.Model(&User{}).Where("id = ?", 42).Update("deleted_at", nil)
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// UPDATE users SET deleted_at=NULL WHERE id=42;
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// 批量恢复
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result := db.Model(&User{}).
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Where("deleted_at IS NOT NULL AND email LIKE '%@test.com'").
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Update("deleted_at", nil)
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fmt.Printf("恢复了 %d 条记录\n", result.RowsAffected)
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```
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> [!important] 恢复后记得重新设置 UpdatedAt
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> 恢复操作本身也是一次 UPDATE，所以 `UpdatedAt` 会自动更新。如果你希望保留原始时间戳，需要在更新前保存到临时变量。
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## 定时清理策略
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软删除会导致数据无限膨胀，建议建立定期清理机制：
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```go
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// cron 定时任务：每月清理 90 天前的软删除记录
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func CleanSoftDeletedRecords(tx *gorm.DB) error {
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cutoff := time.Now().AddDate(0, 0, -90)
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models := []any{&User{}, &Order{}, &Product{}}
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for _, model := range models {
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tx.Where("deleted_at IS NOT NULL AND deleted_at < ?", cutoff).
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Delete(model)
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}
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return nil
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}
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```
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## 软删除决策图
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```mermaid
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flowchart TD
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Start[执行删除操作] --> TypeQ{业务需求_}
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TypeQ --> |可恢复/需审计| SoftDel["软删除<br/>db.Delete()"]
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TypeQ --> |合规要求/不需要恢复| HardDel["物理删除<br/>db.Unscoped().Delete()"]
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SoftDel --> AfterSoft[查询时需要已删除数据?]
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AfterSoft --> |是| UnscopedOn["db.Unscoped()"]
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AfterSoft --> |否| NormalQ["普通查询<br/>自动过滤"]
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HardDel --> AfterHard["数据永久移除"]
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style Start fill:#4FC08D,color:#fff
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style SoftDel fill:#3B82F6,color:#fff
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style HardDel fill:#EF4444,color:#fff
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style UnscopedOn fill:#F59E0B,color:#000
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```
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## 常见坑点速查
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| 问题 | 原因 | 解决方案 |
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|------|------|---------|
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| 唯一约束冲突 | 旧软删除行仍占唯一值 | 加版本字段或用部分索引 |
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| Unscoped 影响后续查询 | 开关是链式的 | 及时结束链或改用显式 Where |
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| 预加载跳过已删除关联 | GORM 自动加 deleted_at 过滤 | 用 Unscoped + Preload 组合 |
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| 软删除导致数据膨胀 | 没有定期清理策略 | 定时任务清理过期记录 |
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| First/Take 找不到已删除记录 | 自动过滤了 deleted_at | Unscoped().First() |
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## 关联笔记
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- [[02-模型定义]]
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- [[03-CRUD 操作]]
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- [[05-关联查询]]
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- [[08-事务管理]]
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