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Many to many relationship

Thread began 12/17/2011 7:49 am by steelace396915 | Last modified 12/21/2011 1:22 am by steelace396915 | 1233 views | 4 replies |


Many to many relationship

I wonder how to accomplish the following with DataAssist:

1. I have an eductaion site where users/students should be able to access different media (pdf and mp3 files etc). Some files should be accessible to all users, some to just a few and so on. I have set up one MySQL table named "users" for all the userdata and one named "media" for the media files. I have also created a inbetween table consisting just of 2 fields, UserID reflecting the user table primary key field UserID and MediaID reflecting the media table primary key field MediaID.

2. I have built all the login, logout, registration functionallity for users with SecurityAssist and it works great now. I have also built an administration section with users update and file uploading to the media tabel in database.

3. A user who logs in successfully is transfered to the students page where he/she should be able to access his/her registration information and mediafiles which he/she has access to. I want to be able to show/list only certain files for different users but don't know how to accomplish this?

For example: Several users should maybe have access to the same mediafile and sometimes just one user should be able to access a certain mediafile. For what I have learned I need to have the Many-to-many relational table I described above to achieve this? I just don't understand how to set this binding up on the page? Someone please give me some input in how to achieve this!?

/Martin Johannesson

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Jason ByrnesWebAssist

you can use a join query to bind the usermedia and media tables together

SELCT media.*
FROM media
INNER JOIN usermedia.MediaID = media.Media.ID

when a user logs in, the users ID is stored in a session variable.

edit your join query to add a where clause that will return the media only for the logged in user. Lets say for example that the name of the User session is "UserID":

WHERE usermedia.UserID = paramUID

then in the variables section, create a new variable:

Name: paramUID
Type: Number
Default value: -1
Runtime value: $_SESSION['UserID']

for more details on joined queries, see the following:

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Thanks Jason! I thought I needed a linking table like I described in post? This seems easier really but I don't know exaclty why! ;=) I'm a real newbie to PHP and MySQL yet but I'm learning new stuff every day!

I tried the code you gave me but I get error messege when testing the page:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.Media.ID WHERE users.UserID = -1' at line 1

My 2 tables are named: users and media
Table media has an ID field named: MediaID
In the users table I created a field named: UserMediaID

Come to think about it, I do have a separate table named accesslevels where I store the different levels (Admin, student, visitor). It has 2 fields, 1 ID field named AccessLevelsID and 1 named AccessLevelsName. In the users table I also have a field named UserAccessLevelsID then.
This is the problem right?

Martin J.

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Jason ByrnesWebAssist

well, the example i gave you _is_ using the linking table, but you dont need the data from all three tables to return the files that are associated to the users. you only need to use the linking table and the media table.

also bear in mind, that the recordset code i gave is not exact, you need to modify it based on your table and column names (This is info I dont have so cant give you exact SQL syntax).

assuming you have a users table, media table and usersmedia (the linking table) with the following basic structure:

userID - primaryKey

mediaID - primary KEY

usermediaID - primary key
usermediaUserID - relates to users.userID
usermediaMediaID - relates to media.mediaID

you can use the following SQL:
SELECT media.*
FROM media
INNER JOIN usermedia.usermediaMediaID =
WHERE usermedia.usermediaUserID = paramUID

I would recommend getting some books from the local bookstore on the MySQL Subject to become a little more familiar with this subject matter, there is only so much the internet can teach you.

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Thanks a lot Jason! I think I understand this now! Will definitely pick up some MySQL book and learn this from scratch!

I wish you and the others at Webassist a merry Christmas and a happy new 2012.

Martin Johannesson

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