作用域
原文：https://gobuffalo.io/documentation/database/scoping/
Scoping 作用域
Scoping is a way to structure your DB calls, when it needs the same “base” query. Let’s say you want to create a book store: the store provides books for everyone, but some special editions are reserved to customers with a registered account. It means that for the whole store, you’ll need to filter the books, so the “guest” customers can only see the restricted list of books.
作用域是一种构建数据库调用（当它需要相同的“基本”查询时）的方式。假设您想创建一个书店：该商店为每个人提供书籍，但某些特别版本仅限于拥有注册帐户的客户。这意味着对于整个商店，您需要过滤书籍，以便“访客”客户只能看到受限的书籍列表。
The Usual Way 通常的方式
A “naive” way can be writing each full query.
一种“天真的”方式可以是编写每个完整查询。
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| type Book struct {
ID uuid.UUID `json:"id" db:"id"`
Label string `json:"label" db:"label"`
Restricted bool `json:"is_restricted" db:"is_restricted"`
}
type Books []Book
// Get available books list
books := Books{}
tx := c.Value("tx").(*pop.Connection)
var err error
if !registeredAccount {
err = tx.Where("is_restricted = false").All(&books)
} else {
// Create an empty query
err = tx.All(&books)
}
if err != nil {
fmt.Printf("ERROR: %v\n", err)
} else {
fmt.Printf("%v\n", books)
}
// Get a specific book
book := Book{}
bookID := "6ba7b810-9dad-11d1-80b4-00c04fd430c8"
tx := c.Value("tx").(*pop.Connection)
var err error
if !registeredAccount {
err = tx.Where("is_restricted = false AND id = ?", bookID).First(&book)
} else {
err = tx.Find(&book, bookID)
}
if err != nil {
fmt.Printf("ERROR: %v\n", err)
} else {
fmt.Printf("%v\n", book)
}
|
The Scoped Way 作用域方式
The scope factorizes the common part of the query:
作用域将查询的公共部分分解为：
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| type Book struct {
ID uuid.UUID `json:"id" db:"id"`
Label string `json:"label" db:"label"`
Restricted bool `json:"is_restricted" db:"is_restricted"`
}
type Books []Book
// restrictedScope defines a base query which shares the common constraint.
func restrictedScope(registeredAccount bool) pop.ScopeFunc {
return func(q *pop.Query) *pop.Query {
if !registeredAccount {
return q
}
return q.Where("is_restricted = false")
}
}
// Get available books list
books := Books{}
if err := tx.Scope(restrictedScope(registeredAccount)).All(&books); err != nil {
fmt.Printf("ERROR: %v\n", err)
} else {
fmt.Printf("%v\n", books)
}
// Get a specific book
book := Book{}
bookID := "6ba7b810-9dad-11d1-80b4-00c04fd430c8"
tx := c.Value("tx").(*pop.Connection)
var err error
if err := tx.Scope(restrictedScope(registeredAccount)).Find(&book, bookID) != nil {
fmt.Printf("ERROR: %v\n", err)
} else {
fmt.Printf("%v\n", book)
}
|
See how we factorized the common restriction for each query, using the restrictedScope function?
您看到我们如何使用 restrictedScope 函数分解每个查询的公共限制了吗？