在Laravel中，如何从数据透视表访问数据？

Question

Maybe I'm implementing wrong. Maybe I'm doing things I'm not supposed to do, but conceptually I think I'm okay.

I have two models, one is Users , other is Communities , and since it is a many to many relationship I need an intermediate table, Laravel calls them a pivot table. According to Laravel recommendations it is named communities_users

Normally, the pivot tables only contain the id's to the main tables. But I need a bit more data. Check this image, the migrations are done to match this diagram:

Here I have a role in the pivot table. Lets say a user belongs to two communities, one as community's president, other as a member.

Of course the president will have more capabilities than the member , for example, he can accept a pending person to become a member person, or he can promote a member to a deputy status or so...

Now lets say I want to get the names of the people with deputy role on a given community. I can easily do that using the Query Builder, by joining the three tables and applying where('communities_users.role', 'deputy') ,

Now, what if I want to use the ORM and get the whole User model?

I'd like to have a function on the Community so it gives me the users of a given role , maybe:

public function users($role) {
    ...
}

So I can do things like:

$community = Community::find($id);
foreach ($community->users('deputy') as user) {
    ...
    echo user->name; // or whatever
    ...
}

Is it possible? How?

Answer 1

As you said only the model keys will be present on the pivot table:

By default, only the model keys will be present on the pivot object. If your pivot table contains extra attributes, you must specify them when defining the relationship:

 return $this->belongsToMany('App\\Role')->withPivot('column1', 'column2'); 

So, in order to use additional fields when querying related records you need to tell Laravel that you are storing more columns in your intermediate/pivot table:

// Community.php

public function users()
{
    return $this->belongsToMany(User::class)
                ->withPivot('role'); // <---
}

Now you can get your desired output:

$community = Community::find($id);
$deputies = $community->users()->wherePivot('role', '=', 'deputy')->get();

foreach ($deputies as $deputy)
{
    echo $deputy->name;
}

Read this section of the documentation.

---

Observation

You said:

... according to Laravel recommendations it is named communities_users ...

At first, I though that this was ok since your models appear to have names in plural (I'm talking about model name, not table name). but then, in your desired output you used Community to refer to a model. So I'm gonna quote this from the Many to Many section of the documentation:

Many To Many

To define this relationship, three database tables are needed: users , roles , and role_user . The role_user table is derived from the alphabetical order of the related model names, and contains the user_id and role_id columns.

As you see, the general convention is to name the intermediate table in alphabetic order from the related model but in singular , so in your case: community_user .

This is the convention that Laravel uses, of couse you can just override the name in the relationship definition passing the intermadiate table name as an additional argument.

Answer 2

Hiding under the Many To Many section of the Eloquent relationship docs:

Filtering Relationships Via Intermediate Table Columns

You can also filter the results returned by belongsToMany using the wherePivot and wherePivotIn methods when defining the relationship:

return $this->belongsToMany('App\Role')->wherePivot('approved', 1);

return $this->belongsToMany('App\Role')->wherePivotIn('priority', [1, 2]);

Assuming your Communities model already has a belongsToMany relationship set up for Users, you should be able to do something like:

$deputies = $community->users()
    ->wherePivot('role', 'deputy') // or equivalent value
    ->get();

Answer 3

First you have to define relationship between models like this :

you told that you have Users model then in Users:

public function communities(){
    return $this->belongsToMany(Communities::class, 'communities_users','user_id', 'community_id');
}

and In your Communities model :

public function users(){
    return $this->belongsToMany(Users::class, 'communities_users','community_id','user_id')
     ->withPivot("role");
}

Now you can access any role type users in your controllers like this :

$community = Community::find($id);
$deputies = $community->users()
->wherePivot('role', 'deputy') // by passing different role
->get();

foreach ($deputies as $deputy)
{
    echo $deputy->name; // print names
}