Gorm关联多对多

Question

我知道gorm多对多关联创建了一个连接表，但是如果我想要/需要一个带有附加字段的自定义连接表怎么办

下面是我的例子

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我有两个gorm模型

type Exercise struct {
    gorm.Model
    Name        string `gorm:"not null" json:"name"`
    Description string `gorm:"not null json:"description"`
}
type Workout struct {
    gorm.Model
    Name string `gorm:"not null" json:"name"`
    CreatedAt time.Time `gorm:"not null" json:"created_at"`
}

如果我使用gorm多对多关联，它将创建一个workout_exercise连接表，但我如何确保填充其他字段，如reps和sets。这是需要在控制器中完成的事情，而不是gorm处理的事情。我用Nodejs和sequelize做过类似的事情，但对go和gorm世界来说真的很陌生。

Answer 1

参加派对有点晚了但是..。我的目标是创造类似的东西，在花了一整天的时间，然后撞到了一堵墙，退了一步重新思考……

经过深思熟虑后，许多游戏，以及一个朋友的好建议，决定从一个稍微不同的角度来处理。

如果你以不同的方式看待它，你可以将它“重新表述”为两个有-一个(或属于-to)和两个一对多：

锻炼锻炼有很多锻炼和锻炼，workout-exercise

• workout-exercise有很多关于锻炼和一次锻炼的经验

此外，在我的游戏中，我意识到多对多表的属性(列)在上面的模型中没有被引用，所以它无论如何都没有用。

如果你把锻炼看作一个“一流”的模型，它开始变得更有意义，变得更有用：

锻炼你可以创建练习-这是一种静态的锻炼池可以创建锻炼，然后你可以使用resources

• You -

• 模型将锻炼填充到锻炼中。

总而言之，我的建议如下所示：

type Exercise struct {
    gorm.Model
    Name        string `gorm:"not null" json:"name"`
    Description string `gorm:"not null" json:"description"`
    Workouts    []WorkoutExercise
}

type Workout struct {
    gorm.Model
    Name      string    `gorm:"not null" json:"name"`
    CreatedAt time.Time `gorm:"not null" json:"created_at"`
    Exercises []WorkoutExercise
}

type WorkoutExercise struct {
    gorm.Model
    WorkoutID  uint
    Workout    Workout `gorm:"foreignKey:WorkoutID;references:ID"`
    ExerciseID uint
    Exercise   Exercise `gorm:"foreignKey:ExerciseID;references:ID"`
    Sets       uint
    Reps       uint
    Weights    uint
}

它的结果是以下模式(我认为这是所需的)：

gym=# \dt
               List of relations
 Schema |       Name        | Type  |   Owner   
--------+-------------------+-------+-----------
 public | installations     | table | gym
 public | workout_exercises | table | gym
 public | workouts          | table | gym
(3 rows)

gym=# \d workouts
                                       Table "public.workouts"
   Column   |           Type           | Collation | Nullable |               Default                
------------+--------------------------+-----------+----------+--------------------------------------
 id         | bigint                   |           | not null | nextval('workouts_id_seq'::regclass)
 created_at | timestamp with time zone |           | not null | 
 updated_at | timestamp with time zone |           |          | 
 deleted_at | timestamp with time zone |           |          | 
 name       | text                     |           | not null | 
Indexes:
    "workouts_pkey" PRIMARY KEY, btree (id)
    "idx_workouts_deleted_at" btree (deleted_at)
Referenced by:
    TABLE "workout_exercises" CONSTRAINT "fk_workouts_exercises" FOREIGN KEY (workout_id) REFERENCES workouts(id)

gym=# \d exercises
                                       Table "public.exercises"
   Column    |           Type           | Collation | Nullable |                Default                
-------------+--------------------------+-----------+----------+---------------------------------------
 id          | bigint                   |           | not null | nextval('exercises_id_seq'::regclass)
 created_at  | timestamp with time zone |           |          | 
 updated_at  | timestamp with time zone |           |          | 
 deleted_at  | timestamp with time zone |           |          | 
 name        | text                     |           | not null | 
 description | text                     |           | not null | 
Indexes:
    "exercises_pkey" PRIMARY KEY, btree (id)
    "idx_exercises_deleted_at" btree (deleted_at)
Referenced by:
    TABLE "workout_exercises" CONSTRAINT "fk_exercises_workouts" FOREIGN KEY (exercise_id) REFERENCES exercises(id)

gym=# \d workout_exercises
                                       Table "public.workout_exercises"
   Column    |           Type           | Collation | Nullable |                    Default                    
-------------+--------------------------+-----------+----------+-----------------------------------------------
 id          | bigint                   |           | not null | nextval('workout_exercises_id_seq'::regclass)
 created_at  | timestamp with time zone |           |          | 
 updated_at  | timestamp with time zone |           |          | 
 deleted_at  | timestamp with time zone |           |          | 
 workout_id  | bigint                   |           |          | 
 exercise_id | bigint                   |           |          | 
 sets        | bigint                   |           |          | 
 reps        | bigint                   |           |          | 
 weights     | bigint                   |           |          | 
Indexes:
    "workout_exercises_pkey" PRIMARY KEY, btree (id)
    "idx_workout_exercises_deleted_at" btree (deleted_at)
Foreign-key constraints:
    "fk_exercises_workouts" FOREIGN KEY (exercise_id) REFERENCES exercises(id)
    "fk_workouts_exercises" FOREIGN KEY (workout_id) REFERENCES workouts(id)

如果你想一想，在没有额外属性的情况下拉出锻炼的练习是没有意义的。如果你只想获得锻炼的练习，你可以从中介模型中提取*

workout := Workout
db.Preload("WorkoutExercise.Exercise").First(&workout, 10)

for _, we := range workout.Exercises {
    // access reps, etc directly from we
    // and access the exercise from the property we.Exercise
    log.Printf("do %d sets of %d repetitions of %s", we.Sets, we.Reps, 
               we.Exercise.Name)
}

*免责声明-并未实际运行此代码(其余部分正常工作)。一定要检查Nested Preloading，以实现一些深度嵌套的急切加载。

Answer 2

type Exercise struct {
    gorm.Model
    Name        string `gorm:"not null" json:"name"`
    Description string `gorm:"not null json:"description"`
    Workouts []Workout `gorm:"many2many:exercise_workout;"`
}
type Workout struct {
    gorm.Model
    Name string `gorm:"not null" json:"name"`
    CreatedAt time.Time `gorm:"not null" json:"created_at"`
}

Many2any的标记值是您定义的关联表名的名称。并使用以下代码加载包含锻炼数据的练习。

var exercises []Exercise
db.Preload("Workouts").Find(&exercises) 

如果您想用锻炼数据加载锻炼，只需在锻炼结构中添加many2many associate，例如：

type Exercise struct {
    gorm.Model
    Name        string `gorm:"not null" json:"name"`
    Description string `gorm:"not null json:"description"`
    Workouts []Workout `gorm:"many2many:exercise_workout;"`
}
type Workout struct {
    gorm.Model
    Name string `gorm:"not null" json:"name"`
    CreatedAt time.Time `gorm:"not null" json:"created_at"`
    Exercises []Exercise `gorm:"many2many:exercise_workout;"`
}

var workouts []Workout
db.Preload("Exercises").Find(&workouts)