manytomany gorm

example.go

//struct channel


type Channel struct {
	ID        uint      `json:"id" gorm:"primary_key" settable:"false"`
	Title             string             `json:"t" sql:"not null"`
  RelatedSets       []Set              `json:"rs,omitempty" gorm:"many2many:related_sets;"` 
}

//struct Set
type Set struct {
  ID        uint      `json:"id" gorm:"primary_key" settable:"false"`
  Title             string             `json:"t" sql:"not null"`
  Channel               *Channel           `json:"ch,omitempty" `
  ChannelID             uint               `json:"id-ch" sql:"index;not null"`
}

//sql da tabela de ref

CREATE TABLE related_sets (
    channel_id integer NOT NULL,
    set_id integer NOT NULL
);

ALTER TABLE related_sets ADD CONSTRAINT fk_related_sets_set_id FOREIGN KEY (set_id) REFERENCES sets;
ALTER TABLE related_sets ADD CONSTRAINT fk_related_sets_channel_id FOREIGN KEY (channel_id) REFERENCES channels;
ALTER TABLE related_sets ADD CONSTRAINT related_sets_channel_set_pkey PRIMARY KEY (channel_id, set_id);

// preload
c.Database.Preload("RelatedSets").First(&ch)

// insert

	err := db.Exec("INSERT INTO related_sets (set_id, channel_id) VALUES (?, ?)",
		setId,
		c.ID).
		Error