阅读gorm文档

Golang/gorm.md

@@ -0,0 +1,79 @@
+- [GORM](#gorm)
+  - [QuickStart](#quickstart)
+  - [Declaring Models](#declaring-models)
+
+
+# GORM
+## QuickStart
+GORM为golang的orm框架，其使用示例如下：
+```go
+package main
+
+import (
+  "gorm.io/gorm"
+  "gorm.io/driver/sqlite"
+)
+
+type Product struct {
+  gorm.Model
+  Code  string
+  Price uint
+}
+
+func main() {
+  db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
+  if err != nil {
+    panic("failed to connect database")
+  }
+
+  // Migrate the schema
+  db.AutoMigrate(&Product{})
+
+  // Create
+  db.Create(&Product{Code: "D42", Price: 100})
+
+  // Read
+  var product Product
+  db.First(&product, 1) // find product with integer primary key
+  db.First(&product, "code = ?", "D42") // find product with code D42
+
+  // Update - update product's price to 200
+  db.Model(&product).Update("Price", 200)
+  // Update - update multiple fields
+  db.Model(&product).Updates(Product{Price: 200, Code: "F42"}) // non-zero fields
+  db.Model(&product).Updates(map[string]interface{}{"Price": 200, "Code": "F42"})
+
+  // Delete - delete product
+  db.Delete(&product, 1)
+}
+```
+## Declaring Models
+gorm中，Model通过struct来进行定义，struct中的fields可以为如下类型：
+- 基础golang类型
+- 指针
+- type alias
+- 自定义类型
+  - 自定义类型需要实现`database/sql`中的Scanner和Valuer接口
+
+如下为一个Model定义的示例：
+```go
+type User struct {
+  ID           uint           // Standard field for the primary key
+  Name         string         // A regular string field
+  Email        *string        // A pointer to a string, allowing for null values
+  Age          uint8          // An unsigned 8-bit integer
+  Birthday     *time.Time     // A pointer to time.Time, can be null
+  MemberNumber sql.NullString // Uses sql.NullString to handle nullable strings
+  ActivatedAt  sql.NullTime   // Uses sql.NullTime for nullable time fields
+  CreatedAt    time.Time      // Automatically managed by GORM for creation time
+  UpdatedAt    time.Time      // Automatically managed by GORM for update time
+  ignored      string         // fields that aren't exported are ignored
+}
+```
+在上述Model中
+- 基础类型的字段可以直接访问，例如`uint, uint8, string`等
+- 指针类型，例如`*time.Time, *string`等，代表该字段值可为空
+- `sql/database`中的`sql.NullString`和`sql.NullTime`类型，也代表该字段可为空
+- `CreateAt`字段和`UpdatedAt`字段是由Gorm管理的字段，当Record被创建或更新时，该字段的值会自动被注入为当前时间
+- `Non-exported fields`（首字母不是大写）并不会被映射
+