Gorm---- Association query

GORM Relational query

1. Defined a  User  and  Company, User  Can contain more than one  Company, as follows :

type User struct {
// here grom Yes map to table 
        ID        int        `gorm:"TYPE:int(11);NOT NULL;PRIMARY_KEY;INDEX"`
        Name      string     `gorm:"TYPE: VARCHAR(255); DEFAULT:'';INDEX"`
        Companies []Company  `gorm:"FOREIGNKEY:UserId;ASSOCIATION_FOREIGNKEY:ID"`
        CreatedAt time.Time  `gorm:"TYPE:DATETIME"`
        UpdatedAt time.Time  `gorm:"TYPE:DATETIME"`
        DeletedAt *time.Time `gorm:"TYPE:DATETIME;DEFAULT:NULL"`
}

type Company struct {
        gorm.Model
        Industry int    `gorm:"TYPE:INT(11);DEFAULT:0"`
        Name     string `gorm:"TYPE:VARCHAR(255);DEFAULT:'';INDEX"`
        Job      string `gorm:"TYPE:VARCHAR(255);DEFAULT:''"`
        UserId   int    `gorm:"TYPE:int(11);NOT NULL;INDEX"`
}

In the query  User  I hope that  Company  The information of , There are three ways :

Related

Use  Related  Method , You need to put  User  Good inquiry , And then according to  User  Specified in the definition  FOREIGNKEY  Go find  Company, If there's no definition , You need to specify , as follows :

var u User
db.First(&u)
db.Model(&u).Related(&u.Companies).Find(&u.Companies)

User  List traverses the list and queries one by one  Company

Association

Use  Association  Method , You need to put  User  Good inquiry , And then according to  User  Specified in the definition  AssociationForeignKey  Go find  Company,  Must define , as follows :

var u User
db.First(&u)
db.Model(&u).Association("Companies").Find(&u.Companies)

Preload

Use  Preload  Method , In the query  User  Go and get  Company  The record of , as follows :

//  Check the list  user
var u User
db.Debug().Preload("Companies").First(&u)
//  Corresponding  sql  sentence 
// SELECT * FROM users LIMIT 1;
// SELECT * FROM companies WHERE user_id IN (1);

//  Query all  user
var list []User
db.Debug().Preload("Companies").Find(&list)
//  Corresponding  sql  sentence 
// SELECT * FROM users;
// SELECT * FROM companies WHERE user_id IN (1,2,3...);

2. Many to many :

Such as articles and labels

type Label struct {
	ID        uint       `gorm:"primary_key" json:"id"` // label id
	CreatedAt time.Time  `json:"-"`
	UpdatedAt time.Time  `json:"updated_at"`
	Name      string     `json:"name"           form:"name"          gorm:"not null;"`                 // Tag name 
	Articles  []Article `json:"articles"       form:"articles"      gorm:"many2many:article_label;" ` // Associated with the article 
}

there Articles and Labels Respectively represents the table name

type Article struct {
	ID        uint      `gorm:"primary_key" json:"id"` // article id
	CreatedAt time.Time `json:"-"`
	UpdatedAt time.Time `json:"updated_at"`
	//DeletedAt  *time.Time `json:"-"`
	UserId    int      `json:"user_id"          form:"user_id"         gorm:"not null;"`                                            // Users 
	UserName  string   `json:"user_name"        form:"user_name"       gorm:"not null"`                                             // Name of the user 
	Title     string   `json:"title"            form:"title"           gorm:"not null"`                                             // Article title 
	Content   string   `json:"content"          form:"content"         gorm:"not null"`                                             // Article content 
	ClassId   int      `json:"class_id"         form:"class_id"        gorm:"not null;"`                                            // Classification 
	Recommend int      `json:"recommend"        form:"recommend"       gorm:"not null"`                                             // Is it recommended  1 recommend 2 Not recommended 
	Abstract  string   `json:"abstract"         form:"abstract"        gorm:"not null"`                                             // Article summary 
	Audit     string   `json:"audit"            form:"audit"           gorm:"not null"`                                             // Article review status   1 For adoption   2 To be reviewed  3 For not passing 
	Labels    []Label `json:"labels"           form:"labels"          gorm:"many2many:article_label"` // Articles are associated with tags 
}

// Articles approved according to the reverse association of labels  , What we get here this Is to get the article 
func (this *Label) LabArt() error {
	return NewConn().Table(this.TableName()).
		Preload("Articles", "audit = ?", "1").
		Where("id = ?", this.ID).First(this).Error
}

 

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