Loopback relation HasAndBelongsToMany with a same model (add friend / make friend Facebook like)

[Brian Duong]

This is a very common case:

We have an User model, now we want an user make friend with each other.

I tried to create a HasAndBelongsToMany like that:

I think its is very reasonable but it doesn't work...

of course this table UsersUsers was generated by Loopback!

It would be perfect is the foreign key is friendId (instead of undefined) and its value is an User ObjectId (instead of String)

Please advise, thanks in advance!

[Alex Megalokonomos]

HasManyThrough ?

with an intermediate table friendships like (friendshipid)  ,userid, friendid ? which can also be expanded with relationship type etc.?

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[Alex Megalokonomos]

In essense it's exactly the same as what loopback tries to create automatically but allows you to declare the table yourself so a) you can have friendid instead of undefined (because LB tries to set the column names programmatically and they end up both as UsersID so once is undefined) and b) you can extend the intermediate table with extra metadata  such as relationshiptype, date of friendship etc.

[Brian Duong]

Already tried but it also does not work:

• Created the table

• Added the relationship

• And the result:

Thanks anyway for your reply!

On Friday, October 7, 2016 at 3:40:01 PM UTC+7, Alex Megalokonomos wrote:

HasManyThrough ?

with an intermediate table friendships like (friendshipid)  ,userid, friendid ? which can also be expanded with relationship type etc.?

On Fri, Oct 7, 2016 at 11:29 AM, Brian Duong <b...@eaglit.com> wrote:

This is a very common case:

We have an User model, now we want an user make friend with each other.

I tried to create a HasAndBelongsToMany like that:

I think its is very reasonable but it doesn't work...

of course this table UsersUsers was generated by Loopback!

It would be perfect is the foreign key is friendId (instead of undefined) and its value is an User ObjectId (instead of String)

Please advise, thanks in advance!

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[Brian Duong]

Can you tell me more details on how can i declare the table UsersUsers manually and set one for the id, one for the fk ?

You also didn't notice the second problem of the case, fk key was saved as String instead of User Object Id

On Friday, October 7, 2016 at 3:49:19 PM UTC+7, Alex Megalokonomos wrote:

In essense it's exactly the same as what loopback tries to create automatically but allows you to declare the table yourself so a) you can have friendid instead of undefined (because LB tries to set the column names programmatically and they end up both as UsersID so once is undefined) and b) you can extend the intermediate table with extra metadata  such as relationshiptype, date of friendship etc.

On Fri, Oct 7, 2016 at 11:39 AM, Alex Megalokonomos <al...@clockwork.gr> wrote:

HasManyThrough ?

with an intermediate table friendships like (friendshipid)  ,userid, friendid ? which can also be expanded with relationship type etc.?

On Fri, Oct 7, 2016 at 11:29 AM, Brian Duong <b...@eaglit.com> wrote:

This is a very common case:

We have an User model, now we want an user make friend with each other.

I tried to create a HasAndBelongsToMany like that:

I think its is very reasonable but it doesn't work...

of course this table UsersUsers was generated by Loopback!

It would be perfect is the foreign key is friendId (instead of undefined) and its value is an User ObjectId (instead of String)

Please advise, thanks in advance!

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[Alex Megalokonomos]

if you're using a through model that you have defined you need to declare the right properties for it in the model declaration

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[Brian Duong]

how can Loopback know which property is the primary key and one other is foreign key ?

[Alex Megalokonomos]

Check: https://docs.strongloop.com/display/public/LB/HasManyThrough+relations

You should be able to define the relation using the  models json files (rather than the relations generator)

 ...Haven't tested it though

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[Brian Duong]

Solved after reading this one https://github.com/strongloop/loopback/issues/1993.

Closed