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- package main
- import (
- "database/sql"
- "errors"
- "fmt"
- _ "github.com/lib/pq"
- )
- type Post struct {
- Id int
- Content string
- Author string
- Comments []Comment
- }
- type Comment struct {
- Id int
- Content string
- Author string
- Post *Post
- }
- var Db *sql.DB
- // connect to the Db
- func init() {
- var err error
- //Db, err = sql.Open("postgres", "user=gwp dbname=gwp password=gwp sslmode=disable")
- Db, err = sql.Open("postgres", "user=gwp dbname=gwp sslmode=disable")
- if err != nil {
- panic(err)
- }
- }
- func (comment *Comment) Create() (err error) {
- if comment.Post == nil {
- err = errors.New("You need to specify the post that the comment belongs to.")
- return
- }
- err = Db.QueryRow("insert into comments (content, author, post_id) values ($1, $2, $3) returning id", comment.Content, comment.Author, comment.Post.Id).Scan(&comment.Id)
- return
- }
- // Get a single post
- func GetPost(id int) (post Post, err error) {
- post = Post{}
- post.Comments = []Comment{}
- err = Db.QueryRow("select id, content, author from posts where id = $1", id).Scan(&post.Id, &post.Content, &post.Author)
- rows, err := Db.Query("select id, content, author from comments where post_id = $1", id)
- if err != nil {
- return
- }
- for rows.Next() {
- comment := Comment{Post: &post}
- err = rows.Scan(&comment.Id, &comment.Content, &comment.Author)
- if err != nil {
- return
- }
- post.Comments = append(post.Comments, comment)
- }
- rows.Close()
- return
- }
- // Create a new post
- func (post *Post) Create() (err error) {
- err = Db.QueryRow("insert into posts (content, author) values ($1, $2) returning id", post.Content, post.Author).Scan(&post.Id)
- return
- }
- func main() {
- post := Post{Content: "Hello World!", Author: "Sau Sheong"}
- post.Create()
- // Add a comment
- comment := Comment{Content: "Good post!", Author: "Joe", Post: &post}
- comment.Create()
- readPost, _ := GetPost(post.Id)
- fmt.Println(readPost) // {1 Hello World! Sau Sheong [{1 Good post! Joe 0xc20802a1c0}]}
- fmt.Println(readPost.Comments) // [{1 Good post! Joe 0xc20802a1c0}]
- fmt.Println(readPost.Comments[0].Post) // &{1 Hello World! Sau Sheong [{1 Good post! Joe 0xc20802a1c0}]}
- }
- /usr/local/Cellar/go/1.7.4_2/libexec/bin/go run /Users/kaiyin/golang/src/github.com/sausheong/gwp/Chapter_6_Storing_Data/sql_store2/store.go
- panic: runtime error: invalid memory address or nil pointer dereference
- [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5fa9a]
- goroutine 1 [running]:
- panic(0x1d62c0, 0xc42000c0e0)
- /usr/local/Cellar/go/1.7.4_2/libexec/src/runtime/panic.go:500 +0x1a1
- database/sql.(*DB).conn(0x0, 0x1, 0x22, 0x1c, 0x0)
- /usr/local/Cellar/go/1.7.4_2/libexec/src/database/sql/sql.go:781 +0x3a
- database/sql.(*DB).query(0x0, 0x216def, 0x40, 0xc42004fd80, 0x2, 0x2, 0x1, 0x10, 0xc42000cba0, 0x0)
- /usr/local/Cellar/go/1.7.4_2/libexec/src/database/sql/sql.go:1074 +0x3b
- database/sql.(*DB).Query(0x0, 0x216def, 0x40, 0xc42004fd80, 0x2, 0x2, 0x1, 0xc42000cba0, 0xc42004fd28)
- /usr/local/Cellar/go/1.7.4_2/libexec/src/database/sql/sql.go:1062 +0x90
- database/sql.(*DB).QueryRow(0x0, 0x216def, 0x40, 0xc42004fd80, 0x2, 0x2, 0x11200b7b18)
- /usr/local/Cellar/go/1.7.4_2/libexec/src/database/sql/sql.go:1143 +0x70
- main.(*Post).Create(0xc420018380, 0xc420018380, 0xc42004fe20)
- /Users/kaiyin/golang/src/github.com/sausheong/gwp/Chapter_6_Storing_Data/sql_store2/store.go:69 +0xfe
- main.main()
- /Users/kaiyin/golang/src/github.com/sausheong/gwp/Chapter_6_Storing_Data/sql_store2/store.go:75 +0xd7
- exit status 2
- Process finished with exit code 1
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