GORM ORM：可以在两个关系方向上预加载吗？

Question

I would like to know if it is possible to preload data from both sides of a relationship. Consider this example:

type User struct {
    gorm.Model
    Name      string
    Documents []Document // has-many
}
type Document struct {
    gorm.Model
    UserID           uint
    Name             string
    DocumentFulltext DocumentFulltext // has-one
}
type DocumentFulltext struct {
    gorm.Model
    DocumentID uint
    Name       string
}

With that I can easily get the DocumentFulltext for any given document like this

db.Where("id = ?", ID).Preload("DocumentFulltext").Find(&document)

Works!

But what if I have the document and want to preload (or join) the User it belongs to?

db.Where("id = ?", ID).Preload("User").Find(&document)

That gives me a panic. ( invalid memory address )

db.Where("id = ?", ID).Joins("User").Find(&document)

And that produces wonky SQL like .... FROM "documents" User WHERE id =...

How is this possible? Do I need to use "manual" queries?

--

If it is not possible: what is a good-practice / guideline how to model my relationships so I can use GORM built-ins like.Preload() effectively?

Eg If I put the relationship between Users and Documents like this:

type User struct {
    gorm.Model
    Name string
}
type Document struct {
    gorm.Model
    User             User // belongs-to
    UserID           uint
    Name             string
    DocumentFulltext DocumentFulltext // has-one
}
type DocumentFulltext struct {
    gorm.Model
    DocumentID uint
    Name       string
}

then I can preload both, DocumentFulltext AND User, for any given Document. But I loose the ability the preload Documents and Fulltexts if I want to do it for a given User.

--

Any hints a re appreciated. Thx!

Answer 1

Use relation both side means User in Document struct and Documents in User struct

type User struct {
    gorm.Model
    Name      string
    Documents []Document // has-many
}

type Document struct {
    gorm.Model
    UseredID uint
    Name     string
    User   User
}

Then you can preload both sides

db.Debug().Where("id = ?", ID).Preload("User").Find(&document)
db.Debug().Where("id = ?", ID).Preload("Documents").Find(&user)