英文:
Embedding model structs with same attribute names in golang
问题
使用go 1.5和gorm。
假设我想创建一个名为events的表，其中包含created_by_id和updated_by_id两列。
我可以这样定义我的模型：
type By struct {
ByID sql.NullInt64
By *User
}
type CreatedBy struct {
By
}
type UpdatedBy struct {
By
}
type Event struct {
CreatedBy
UpdatedBy
}
当我尝试保存一个event对象时，by_id列的值将被保存，而不是created_by_id和updated_by_id的值。我需要怎么做才能确保CreatedBy和UpdatedBy的ByID属性的列名不同呢？
英文:
Using go 1.5, and gorm.
Say I want to make an events table that has a created_by_id and an updated_by_id columns.
I write my models like
type By struct {
ByID sql.NullInt64
By *User
}
type CreatedBy struct {
By
}
type UpdatedBy struct {
By
}
type Event struct {
CreatedBy
UpdatedBy
}
When I try to save an event object, the value for the column by_id will try to be saved rather than the values for created_by_id and updated_by_id. What do I need to do to make sure the column names of ByID attribute are different for CreatedBy and UpdatedBy?
答案1
得分: 1
问题在于你将CreatedBy和UpdatedBy都嵌入到了Event结构体中，所以对Event.By的调用是模棱两可的，不被允许的（你必须能够明确指定Event.CreatedBy.By和Event.UpdatedBy.By来消除这两个字段的歧义）。
解决方案很可能是_不要嵌入_这些类型，而是创建一个具有明确字段的结构体：
type Event struct {
CreatedBy CreatedBy
UpdatedBy UpdatedBy
}
gorm现在应该知道如何消除这两个列的歧义。
当然，如果你只是为了列映射的目的将By嵌入到CreatedBy和UpdatedBy中，那么你不需要声明新的结构体：
type By struct {
ByID sql.NullInt64
By *User
}
type Event struct {
CreatedBy By
UpdatedBy By
}
英文:
The problem is that you're embedding both CreatedBy and UpdatedBy into Event, so calls to Event.By are ambiguous and not allowed (you'd have to be able to specify Event.CreatedBy.By and Event.UpdatedBy.By explicitly to disambiguate the two fields).
The solution, most likely, would be to not embed the types, but actually create a struct with explicit fields:
type Event struct {
CreatedBy CreatedBy
UpdatedBy UpdatedBy
}
gorm should now know how to disambiguate the two columns.
Of course if you're only going to embed By into CreatedBy and UpdatedBy for the purposes of column mapping then you shouldn't need to declare new structs:
type By struct {
ByID sql.NullInt64
By *User
}
type Event struct {
CreatedBy By
UpdatedBy By
}
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