2020. január 16., csütörtök 8:20:17 UTC+1 időpontban Shulhan a következőt
írta:
>
> ## Problem
>
> At some point we have a function that receive an instance of database
> connection to query rows in specific table.
>
> Let's say that function F() accept DB that query table T.
>
> If function F() called with DB instance, it will query only rows that has
> been committed into database.
>
> IF function F() called with Tx instance, it will query all rows including
> the one that has not been committed yet into database.
>
> Since DB and Tx are different types, we will have two functions that
> almost have identical code,
>
> func F(db *sql.DB) (output int) {
> q := `SELECT … FROM T WHERE …`
> err := db.QueryRow(q).Scan(&output)
> …
> return output
> }
>
> func FWithTx(tx *sql.Tx)(output int) {
> q := `SELECT … FROM T WHERE …`
> err := tx.QueryRow(q).Scan(&output)
> …
> return output
> }
>
>
> ## Proposed solution
>
> Add an interface Session (the name is not fixed yet) to package sql with
> the following signature,
>
> type Session interface {
> func Exec(query string, args ...interface{}) (Result, error)
> func ExecContext(ctx context.Context, query string, args
> ...interface{}) (Result, error)
> func Prepare(query string) (*Stmt, error)
> func PrepareContext(ctx context.Context, query string) (*Stmt, error)
> func Query(query string, args ...interface{}) (*Rows, error)
> func QueryContext(ctx context.Context, query string, args
> ...interface{}) (*Rows, error)
> func QueryRow(query string, args ...interface{}) *Row
> func QueryRowContext(ctx context.Context, query string, args
> ...interface{}) *Row
> }
>
> Session interface is combination of DB and Tx that contains all identical
> methods.
>
>
> ## Rationale
>
> Without Session, user will have two functions that have the same code,
>
> By using Session, we can minimise duplicate code in the user level. for
> example using the previous problems definition the function F() become one,
>
> func F(session sql.Session)(output int) {
> q := `SELECT … FROM T WHERE …`
> err := session.QueryRow().Scan(&output)
> …
> return output
> }
>
>
> ## Discussion
>
> Any thought about this proposal?
Just define the interface and use it - Go is not Java, iff a type
statisfies an interface, then it also implements it!
You can use anonymous interfaces also!
```
func F(db interface { QueryRow() *sql.Row })(output int) {
q := `SELECT … FROM T WHERE …`
err := db.QueryRow().Scan(&
>
> output)
> …
> return output
> }
```
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