Simple friendship table

Rails
1

Tables:
Users (id, name, sex)
Friendships (user_id, friend_id, status)

If user(1) and user(2) are friends shoud I add two rows into friendships
table?

1, 2, “best friends”
2, 1, “best friends”

Or is it enough to have one of these rows? Select * from friendships
where user_id = 2 or friend_id = 2 ???

But if I have only one friendship row and I need to list all friens of
user(2) How can I do it? I don’t know which one “user_id” or “friend_id”
is needed “data”.

Of course, I can check: IF search_id != friend_id print
(friend_id).user.name ELSE print (user_id).user.name But it is slow and
stupid…

2

Hi, you only need one entry per friendship (where, for extra
functionality, the first id could always be the one who initiated the
friendship).
Friendships table could be something like have (uid1, uid2, status).
Probably put first two as primary key.

To find ids of all friends of user 1 you would do :

(SELECT uid2 AS uid, status FROM friendships WHERE uid1 = 1)
UNION
(SELECT uid1,status FROM friendships WHERE uid2 = 1)

This would return a set of rows with columns (uid, status) for all
friends of user 1. If you have:

Uid1,uid2,status
1,2,“best friend”
1,3,“partner”
3,2,“lover”
3,7,“barely met”
4,1,“enemy”
7,1,“buddy”

The above select would return:

Uid, status
2,“best friend”
3,“partner”
4,“enemy”
7,“buddy”

Regards

Binni

-----Oprindelig meddelelse-----
Fra: [email protected]
[mailto:[email protected]] P vegne af Fresh M.
Sendt: 21. december 2011 12:04
Til: [email protected]
Emne: [Rails] Simple friendship table

Tables:
Users (id, name, sex)
Friendships (user_id, friend_id, status)

If user(1) and user(2) are friends shoud I add two rows into friendships
table?

1, 2, “best friends”
2, 1, “best friends”

Or is it enough to have one of these rows? Select * from friendships
where user_id = 2 or friend_id = 2 ???

But if I have only one friendship row and I need to list all friens of
user(2) How can I do it? I don’t know which one “user_id” or “friend_id”
is needed “data”.

Of course, I can check: IF search_id != friend_id print
(friend_id).user.name ELSE print (user_id).user.name But it is slow and
stupid…

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3

Just a small addition to my previous email. If you also want to see,
from the result, whether user 1 initiated the friendship (i.e. where
uid1=1), you could use the following SQL statement:

(SELECT uid2 AS uid, status, 1 AS initiated FROM friendships WHERE uid1
= 1) UNION (SELECT uid1,status,0 FROM friendships WHERE uid2 = 1)

This would give you the following result (using same data as below):

Uid, status, initiated
2,“best friend”,1
3,“partner”,1
4,“enemy”,0
7,“buddy”,0

Where initiated=1 are the ones with uid1=1 and initiated=0 are the ones
with uid2=1

-----Oprindelig meddelelse-----
Fra: [email protected]
[mailto:[email protected]] P vegne af Brynjolfur
Thorvardsson
Sendt: 21. december 2011 13:02
Til: [email protected]
Emne: SV: [Rails] Simple friendship table

Hi, you only need one entry per friendship (where, for extra
functionality, the first id could always be the one who initiated the
friendship).
Friendships table could be something like have (uid1, uid2, status).
Probably put first two as primary key.

To find ids of all friends of user 1 you would do :

(SELECT uid2 AS uid, status FROM friendships WHERE uid1 = 1) UNION
(SELECT uid1,status FROM friendships WHERE uid2 = 1)

This would return a set of rows with columns (uid, status) for all
friends of user 1. If you have:

Uid1,uid2,status
1,2,“best friend”
1,3,“partner”
3,2,“lover”
3,7,“barely met”
4,1,“enemy”
7,1,“buddy”

The above select would return:

Uid, status
2,“best friend”
3,“partner”
4,“enemy”
7,“buddy”

Regards

Binni

-----Oprindelig meddelelse-----
Fra: [email protected]
[mailto:[email protected]] P vegne af Fresh M.
Sendt: 21. december 2011 12:04
Til: [email protected]
Emne: [Rails] Simple friendship table

Tables:
Users (id, name, sex)
Friendships (user_id, friend_id, status)

If user(1) and user(2) are friends shoud I add two rows into friendships
table?

1, 2, “best friends”
2, 1, “best friends”

Or is it enough to have one of these rows? Select * from friendships
where user_id = 2 or friend_id = 2 ???

But if I have only one friendship row and I need to list all friens of
user(2) How can I do it? I don’t know which one “user_id” or “friend_id”
is needed “data”.

Of course, I can check: IF search_id != friend_id print
(friend_id).user.name ELSE print (user_id).user.name But it is slow and
stupid…

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4

It would probably run a lot faster if you had a view and separate
indexes on the two uid columns. I haven’t got access to my MySQL at the
moment, so i can’t check the syntax for creating a view but you should
be able to find that yourself. Something like:

CREATE VIEW friendshipview AS ()

Creating separate indexes on the columns used in the select statements
should speed things up quite a bit, an index should speed up by a factor
of 10^2 or 3. If you have a very active database you might also consider
rebuilding the index regularly, with OPTIMIZE TABLE

.

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Sendt: 22. december 2011 21:33
Til: [email protected]
Emne: [Rails] Re: SV: Simple friendship table

Brynjolfur T. wrote in post #1037658:

(SELECT uid2 AS uid, status FROM friendships WHERE uid1 = 1) UNION
(SELECT uid1,status FROM friendships WHERE uid2 = 1)

It works fine, but it is slow :frowning:

Only one entry per friendship (1 500 000 rows in database)

SELECT with UNION: 1.2108 sek

Dublicate entryes ( total 3 000 000 rows in database)

SELECT without UNION: 0.0007 sek

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5

(SELECT uid2 AS uid, status FROM friendships WHERE uid1 = 1) UNION
(SELECT uid1,status FROM friendships WHERE uid2 = 1)

How to write same in Rails 3 Active Record Query format?

6

A simple way would be to just call .find_by_sql()

On the other hand, if you create a view in MySQL to handle the query,
say the view is called “friends”, then you should be able to create a
model like this:

app/models/friend.rb

class Friend < ActiveRecord::Base
end

Obviously, depending on the view and tables behind it, you might want to
make your new model read only. That can apparently be done like this (I
haven’t actually tested this!)

class Post < ActiveRecord::Base

def readonly?
return true
end

end

There are probably lots of other ways of wrapping the result as an
object, but basically I don’t think you can avoid passing the SQL UNION
statemenet as is. There might be a way of calling two separate SQL
statements, store the results in separate variables and then adding the
two:

@var1 = @friends.where(<select 1>)
@var2 = @friends.where(<select 2>)

@friendsfound = @var1 + @var2

Obviously, the returned column names would have to match, and I’m not at
all sure this would do what it looks like doing!

-----Oprindelig meddelelse-----
Fra: [email protected]
[mailto:[email protected]] P vegne af Fresh M.
Sendt: 22. december 2011 23:53
Til: [email protected]
Emne: [Rails] Re: SV: Simple friendship table

(SELECT uid2 AS uid, status FROM friendships WHERE uid1 = 1) UNION
(SELECT uid1,status FROM friendships WHERE uid2 = 1)

How to write same in Rails 3 Active Record Query format?

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7

Brynjolfur T. wrote in post #1037995:

@var1 = @friends.where(<select 1>)
@var2 = @friends.where(<select 2>)

@friendsfound = @var1 + @var2

tmp1 = Friendships.includes(:users).select(“uid1 as user_id”,
status).where(“uid2 = (?)”, @user.id)
tmp2 = Friendships.includes(:users).select(“uid2 as user_id”,
status).where(“uid1 = (?)”, @user.id)
@friends = tmp1 + tmp2

Tested, it works, but the only problem is ordering.

How to order:

.order(“FIELD( friendships.status, ‘lover’, ‘best friend’, ‘partner’,
‘enemy’ ), users.name”)

8

On 21 December 2011 11:04, Fresh M. [email protected] wrote:

Or is it enough to have one of these rows? Select * from friendships
where user_id = 2 or friend_id = 2 ???

But if I have only one friendship row and I need to list all friens of
user(2) How can I do it? I don’t know which one “user_id” or “friend_id”
is needed “data”.

Of course, I can check: IF search_id != friend_id print
(friend_id).user.name ELSE print (user_id).user.name But it is slow and
stupid…

First setup the model relationships so that you are not messing about
with id values all the time, something like
this railscast [1]. Then if you want all the friends of a user it is
simply.
user.friends + user.inverse_friends

Colin

[1] #163 Self-Referential Association - RailsCasts

9

On 24 December 2011 18:50, Fresh M. [email protected] wrote:

tmp2 = Friendships.includes(:users).select(“uid2 as user_id”,
status).where(“uid1 = (?)”, @user.id)
@friends = tmp1 + tmp2

Tested, it works, but the only problem is ordering.

How to order:

.order(“FIELD( friendships.status, ‘lover’, ‘best friend’, ‘partner’,
‘enemy’ ), users.name”)

Because you are adding the two collections together you will have to
sort it afterwards. Have a look at Array#sort and sort_by.

Colin