2. Inspect a variable and find its type 检查变量并找到它的类型
package mainimport("fmt")type order struct{ordId intcustomerId int}type employee struct{name stringid intaddress stringsalary intcountry string}funccreateQuery(b order)string{i := fmt.Sprintf("insert into order values(%d, %d)", b.ordId, b.customerId)return i}funccreateQuerySet(b employee)string{i := fmt.Sprintf("insert into order values(%s, %d, %s, %d, %s)", b.name, b.id, b.address, b.salary, b.country)return i}funcmain(){a :=10fmt.Printf("%d, %T\n", a, a)b := order{171103,1006,}e := employee{"Like",1,"Shanghai",999999,"Minghang",}fmt.Println(createQuery(b))fmt.Println(createQuerySet(e))}// 10, int// insert into order values(171103, 1006)// insert into order values(Like, 1, Shanghai, 999999, Minghang)
3. Reflect.Type and reflect.Value 反射类型和值
package mainimport("fmt""reflect")type order struct{ ordId intcustomerId int}funccreateQuery(q interface{}){ t := reflect.TypeOf(q)v := reflect.ValueOf(q)fmt.Println("Type ", t)fmt.Println("Value ", v)}funcmain(){ o := order{ordId:456,customerId:56,}createQuery(o)}// Type main.order // Value {456 56}
4. Reflect.Kind 查看底层种类
package mainimport("fmt""reflect")type order struct{ ordId intcustomerId int}funccreateQuery(q interface{}){ t := reflect.TypeOf(q)k := t.Kind()fmt.Println("Type ", t)fmt.Println("Kind ", k)}funcmain(){ o := order{ordId:456,customerId:56,}createQuery(o)}// Type main.order // Kind struct
5. NumField() and Field() methods 字段数量和索引值方法
package mainimport("fmt""reflect")type order struct{ ordId intcustomerId int}funccreateQuery(q interface{}){if reflect.ValueOf(q).Kind()== reflect.Struct {// struct == structv := reflect.ValueOf(q)// {456 56}fmt.Println("Number of fields", v.NumField())// 2for i :=0; i < v.NumField(); i++{fmt.Printf("Field:%d type:%T value:%v\n", i, v.Field(i), v.Field(i))}}}funcmain(){ o := order{ordId:456,customerId:56,}createQuery(o)}// Number of fields 2 // Field:0 type:reflect.Value value:456 // Field:1 type:reflect.Value value:56
6. Int() and String() methods 整型和字符型方法
package mainimport("fmt""reflect")funcmain(){ a :=56x := reflect.ValueOf(a).Int()fmt.Printf("type:%T value:%v\n", x, x)b :="Naveen"y := reflect.ValueOf(b).String()fmt.Printf("type:%T value:%v\n", y, y)}// type:int64 value:56 // type:string value:Naveen
7. Complete Program 完整示例
package mainimport("fmt""reflect")type order struct{ ordId intcustomerId int}type employee struct{ name stringid intaddress stringsalary intcountry string}funccreateQuery(q interface{}){if reflect.ValueOf(q).Kind()== reflect.Struct {t := reflect.TypeOf(q).Name()query := fmt.Sprintf("insert into %s values(", t)// 输出传入的valuesv := reflect.ValueOf(q)// 赋值vfor i :=0; i < v.NumField(); i++{switch v.Field(i).Kind(){case reflect.Int:if i ==0{query = fmt.Sprintf("%s%d", query, v.Field(i).Int())}else{query = fmt.Sprintf("%s, %d", query, v.Field(i).Int())}case reflect.String:if i ==0{query = fmt.Sprintf("%s\"%s\"", query, v.Field(i).String())}else{query = fmt.Sprintf("%s, \"%s\"", query, v.Field(i).String())}default:fmt.Println("Unsupported type")return}}query = fmt.Sprintf("%s)", query)fmt.Println(query)return}fmt.Println("unsupported type")}funcmain(){ o := order{ordId:456,customerId:56,}createQuery(o)e := employee{name:"Naveen",id:565,address:"Coimbatore",salary:90000,country:"India",}createQuery(e)i :=90createQuery(i)}// insert into order values(456, 56) // insert into employee values("Naveen", 565, "Coimbatore", 90000, "India") // unsupported type
二、 Reading Files
1. Reading Files 读取文件
package mainimport("fmt""os")funcmain(){contents, err := os.ReadFile("test.txt")if err !=nil{fmt.Println("File reading error", err)return}fmt.Println("Contents os file:",string(contents))}// Contents os file: Hello World. Welcome to file handling in GO
2. Using absolute file path 使用绝对路径
package mainimport("fmt""os")funcmain(){contents, err := os.ReadFile("D:/Go/oop/test.txt")if err !=nil{fmt.Println("File reading error", err)return}fmt.Println("Contents os file:",string(contents))}// Contents os file: Hello World. Welcome to file handling in GO
3. Passing the file path as a command line flag 将文件路径作为命令行标志传递
package main import("flag""fmt")funcmain(){ fptr := flag.String("fpath","test.txt","file path to read from")flag.Parse()contents, err := os.ReadFile(*fptr)if err !=nil{fmt.Println("File reading error", err)return}fmt.Println("Contents of file: ",string(contents))}// Contents of file: Hello World. Welcome to file handling in GO.
4. Reading a file in small chunks
package mainimport("bufio""flag""fmt""io""log""os")funcmain(){targetPath := flag.String("targetPath","test.txt","file path to read from")flag.Parse()// 进行命令行参数的解析 将相应的值赋给标志变量targetPathf, err := os.Open(*targetPath)// err: nil f: *os.Fileif err !=nil{log.Fatal(err)// 将错误信息打印到标准错误输出}deferfunc(){// 延迟开启匿名函数一直循环 如果关闭文件时发送错误 log处理错误if err = f.Close(); err !=nil{log.Fatal(err)}}()r := bufio.NewReader(f)// 创建了一个 bufio.Reader 对象r用于逐行读取文件内容b :=make([]byte,3)for{n, err := r.Read(b)// r.Read(b) 方法读取文件内容 将读取到的内容存储在字节切片b中 并返回读取的字节数n和可能出现的错误errif err == io.EOF {// 如果读取到文件末尾输出fmt.Println("Finished reading file")break}if err !=nil{// 如果读取文件发生错误fmt.Println("Error %s reading files", err)break}fmt.Println(string(b[0:n]))// 输出切片内容 切片容量3}}// Hel // lo // Wor // ld. // We// lco // me // to // fil // e h // and // lin // g i // n G // o. // finished reading file
5. Reading a file line by line 逐行读取文件
package mainimport("bufio""flag""fmt""log""os")funcmain(){ fptr := flag.String("fpath","test.txt","file path to read from")flag.Parse()f, err := os.Open(*fptr)if err !=nil{log.Fatal(err)}deferfunc(){if err = f.Close(); err !=nil{log.Fatal(err)}}()s := bufio.NewScanner(f)for s.Scan(){fmt.Println(s.Text())}err = s.Err()if err !=nil{log.Fatal(err)}}// Hello World. Welcome to file handling in Go. // This is the second line of the file. // We have reached the end of the file.
type A struct {CreateTime *time.Time gorm:"create_time"
}
1、定义数据库表映射结构体如上，create_time字段在表里面是datetime格式。
2、如果CreateTime不给值，在存库时，create_time字段的值为NULL。
3、赋值时，…
