issue47896.go

     1  //  compile
     2  
     3  // Copyright 2021 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import (
    10  	"database/sql"
    11  )
    12  
    13  // Collection generic interface which things can be added to.
    14  type Collection[T any] interface {
    15  	Add(T)
    16  }
    17  
    18  // Slice generic slice implementation of a Collection
    19  type Slice[T any] []*T
    20  
    21  func (s *Slice[T]) Add(t *T) {
    22  	*s = append(*s, t)
    23  }
    24  
    25  type Scanner interface {
    26  	Scan(...interface{}) error
    27  }
    28  
    29  type Mapper[T any] func(s Scanner, t T) error
    30  
    31  type Repository[T any] struct {
    32  	db *sql.DB
    33  }
    34  
    35  func (r *Repository[T]) scan(rows *sql.Rows, m Mapper[*T], c Collection[*T]) error {
    36  	for rows.Next() {
    37  		t := new(T)
    38  		if err := m(rows, t); err != nil {
    39  			return err
    40  		}
    41  		c.Add(t)
    42  	}
    43  	return rows.Err()
    44  }
    45  
    46  func (r *Repository[T]) query(query string, m Mapper[*T], c Collection[*T]) error {
    47  	rows, err := r.db.Query(query)
    48  	if err != nil {
    49  		return err
    50  	}
    51  	if err := r.scan(rows, m, c); err != nil {
    52  		rows.Close()
    53  		return err
    54  	}
    55  	return rows.Close()
    56  }
    57  
    58  type Actor struct {
    59  	ActorID   uint16
    60  	FirstName string
    61  	LastName  string
    62  }
    63  
    64  type ActorRepository struct {
    65  	r Repository[Actor]
    66  }
    67  
    68  func (ActorRepository) scan(s Scanner, a *Actor) error {
    69  	return s.Scan(&a.ActorID, &a.FirstName, &a.LastName)
    70  }
    71  
    72  func (r *ActorRepository) SelectAll(c Collection[*Actor]) error {
    73  	return r.r.query("SELECT `actor_id`, `first_name`, `last_name` FROM `actor` LIMIT 10", r.scan, c)
    74  }
    75
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