Golang Go语言中使用一个数据处理库来泛型尝鲜

这是一个用 Go 实现的数据处理库，升级之前用 interface{}表示参数类型，阅读起来还是容易模糊。现在泛型出了之后，就把它升级一下：

原来：

// extract column from table
// * First Argument:table
// * Second Argument:column name
result := query.Column(users, "UserID")
userIDs := result.([]int)
// generate a map from table,key is column value and value is it’s row
// * First Argument:table
// * Second Argument:column name
result = query.ColumnMap(users, “UserID”)
userMap := result.(map[int]User)
// select data from table
// * First Argument:table
// * Second Argument:select rule
result = query.Select(users, func(a User) Sex {
if len(a.Name) >= 3 && a.Name[0:3] == “Man” {
return Sex{IsMale: true}
}
return Sex{IsMale: false}
})
sel := result.([]Sex)
// filter data from table
// * First Argument:table
// * Second Argument:filter rule
result = query.Where(users, func(a User) bool {
if len(a.Name) >= 3 && a.Name[0:3] == “Man” {
return true
}
return false
})
where := result.([]User)
// group data from table
// * First Argument: left table
// * Second Argument: group column name
// * Third Argument: group rule
result = query.Group(users, “UserID”, func(users []User) Department {
return Department{
Employees: users,
}
})
group := result.([]Department)
// join data from two table ，support LeftJoin,RightJoin,InnerJoin 和 OuterJoin
// * First Argument: left table
// * Second Argument: right table
// * Third Argument: join condition
// * Forth Argument: join rule
result = query.LeftJoin(admins, users, “AdminID = UserID”, func(admin Admin, user User) AdminUser {
return AdminUser{
AdminID:    admin.AdminID,
Level:      admin.Level,
Name:       user.Name,
CreateTime: user.CreateTime,
}
})
join := result.([]AdminUser)

现在

// extract column from table
// * First Argument:table
// * Second Argument:column name
userIDs := query.Column[User, int](users, "UserID") // []int
// generate a map from table,key is column value and value is it’s row
// * First Argument:table
// * Second Argument:column name
userMap = query.ColumnMapUser, int, map[int]User // map[int]User
// or
usersMap = query.ColumnMapUser, int, map[int][]User // map[int][]User
// select data from table
// * First Argument:table
// * Second Argument:select rule
sel = query.Select(users, func(a User) Sex {
if len(a.Name) >= 3 && a.Name[0:3] == “Man” {
return Sex{IsMale: true}
}
return Sex{IsMale: false}
}) // []Sex
// filter data from table
// * First Argument:table
// * Second Argument:filter rule
where = query.Where(users, func(a User) bool {
if len(a.Name) >= 3 && a.Name[0:3] == “Man” {
return true
}
return false
}) // []User
// group data from table
// * First Argument: left table
// * Second Argument: group column name
// * Third Argument: group rule
group = query.Group[User, Department, []Department](users, “UserID”, func(users []User) Department {
return Department{
Employees: users,
}
}) // []Department
// or
group = query.Group[User, []Department, *[]Department](users, “UserID”, func(users []User) []Department {
return []Department{
Employees: users,
}
}) // *[]Department
// join data from two table ，support LeftJoin,RightJoin,InnerJoin 和 OuterJoin
// * First Argument: left table
// * Second Argument: right table
// * Third Argument: join condition
// * Forth Argument: join rule
join = query.LeftJoin(admins, users, “AdminID = UserID”, func(admin Admin, user User) AdminUser {
return AdminUser{
AdminID:    admin.AdminID,
Level:      admin.Level,
Name:       user.Name,
CreateTime: user.CreateTime,
}
}) // []AdminUser

减少了断言，还是挺好的。

一点问题

目前的 Go 泛型不支持类型参数内嵌，所以在 Group 函数里使用了指针。

// 这样是不行的
func Group[T, E any, R E | []E](data []T, groupType string, groupFunctor func([]T) E) R
// 只好写成这样
func Group[T, E any, R *E | []E](data []T, groupType string, groupFunctor func([]T) E) R