I have a table dislikes which contains two columns, idone and idtwo.
These are unique ids' from users, for example:
| idone | idtwo |
-----------------
| 5 | 4 |
This means that user with id=5 does not like user with id=4. What I have in PHP is an array containing the ids' of all the users that the current user has selected as not liking them.
So say dislikes={1,2,3}, this means that the current user does not like user 1,2, or 3. There is an unknown number of users in the database.
So if user 1 chooses to dislike user 2 and user 3 (this is done via HTML dropdown), I pass dislike={2,3} to a PHP page which processes this data.
I want the PHP page to then add entries (1,2) and (1,3). Here is the first problem, how can I make sure only to add unique entries?
Also say that user 1 changes the fact that he dislikes user 2. Then I pass dislike={3} to the php page and must somehow remove all entries (1,!3), i.e. all entries in which user 1 dislikes anyone except user 3. How can I achieve this? Or is there a better way?
Since you're using MySQL the easiest thing is probably to use REPLACE INTO instead of INSERT with a primary key or unique index on the pair of columns (idone, idtwo).
Alternatively, on update, you can run a transaction that does any one of:
Remove existing rows for this user, add all rows, commit
Select existing rows, remove the rows from your local set that you would duplicate, add only new rows, commit
Related
I'm trying to show or not show links based on a users access level. The links will be different depending on the section of the site the user might be in. The links also may not all be in one menu. They will more than likely be in various places on the page.
Currently I have a database table that contains Users, Groups and Sections. The main menu is built from the Sections database table. I'm thinking I should create an Actions table and add a link that I'd like to show for each section in the action menu. So, my tables so far are like.
Users
user_id
Groups
group_id
group_title
Sections
section_id
section_title
Table I'm thinking of adding.
Actions
action_id
action_title
action_group_id
action_section_id
The part I'm not sure on is should I add the same link multiple times to the Actions table for each group that is allowed access. Or, just add it once and do a if group id is greater than, then show link.
Example for entering the same link multiple times.
action_id action_title action_group_id action_section_id
1 View all 1 1
2 View all 2 1
3 View all 3 1
I was hoping to not flood the page with a bunch of if/then statements. Plus, this doesn't seem like the best way to handle because it requires human interpretation as to what the access levels stand for.
Any help on this is appreciated. I could be going in the complete wrong direction here?
Create a many to many relationship with an additional table where you insert an entry for each permission the group has access to. Am I correct in assuming section is what you're creating permission to?
Table: Group_Section (Or whatever you'd like to name it)
Group_id | Section_ID
---------+-----------
1 | 1
1 | 2
1 | 3
2 | 1
2 | 3
|
You can see that the Group with ID = 1 can access sections 1,2,3 while Group with ID = 2 can access only 1,3. You can then add whatever permissions to the table you want and manage them through the use of foreign keys.
Does that make sense?
Here is a good article but the things are discussed in general http://en.wikipedia.org/wiki/Access_controlenter link description here
In your case, use what TheCapn wrote and I'll just add, that its 'best to start session for every user and just check his access level when he's trying to reach a restricted part.
Personnaly, to do this kind of thing, i set a user level in the user table and a section level in the section table.
Then you simply have to filter the section according to your user level.
You can do this by adding a statemtn to you sql like
AND section_level >= "user_level";
or then again, get all the section and filter tham with php.
foreach($section as $s){
if ($s->level >= user_level) echo $s->title
}
Of course, you'll need to adjust the <. = and > according to the hierachy of your system.
I personnaly use a lowering hierachy, meaning, the lower the level you are the more right you have. This way you can make a 'banned' user by setting his level to 99 or something.
THis would be only for your menus, make sure you control the user_level on each page as well so if someone get to the page directly it get kicked..
Hope it points your in the right direction. ;)
So I need to make a checklist for a web app where an administrator can edit a checklist for a user. The administrator can check those when a certain condition is met and also write a comment about it if necessary.
I set up 3 tables:
A user table which stores all the user information like name, birthplace and so on. Primary key is user_idnr
Then I have a table called CHECKLIST_properties. It stores all the different items of the checkbox. It has the following columns:
property_idnr | type | description
Finally, I have a table called CHECKLIST_user_property. It is used to link a property to a user, when a row is created, it is checked. It has the following columns:
link_idnr | user_idnr | property_idnr | comments
I am having trouble planning out how to save the checked boxes in the database. You need to determine when a row needs to be added or removed from the table. Can anyone give me some tips on how to set this up properly?
I see a couple of options:
remove all the rows and add the currently selected ones back in. This can have unintended side-effects (new auto incrementing numbers, etc).
add a column that is used to track the status of the rows. Use INSERT ... ON DUPLICATE KEY UPDATE to add rows to the table and/or update existing rows. The new/updated rows would have a different value in the new column (like a timestamp). Then delete all the rows with an older value (as they weren't added/updated, they're not needed).
I have a MySQL database with a growing number of users and each user has a list of items they want and of items they have - and each user has a specific ID
The current database was created some time ago and it currently has each users with a specific row in a WANT or HAVE table with 50 columns per row with the user id as the primary key and each item WANT or HAVE has a specific id number.
this currently limits the addition of 50 items per user and greatly complicates searches and other functions with the databases
When redoing the database - would it be viable to instead simply create a 2 column WANT and HAVE table with each row having the user ID and the Item ID. That way there is no 'theoretical' limit to items per user.
Each time a member loads the profile page - a list of their want and have items will then be compiled using a simple SELECT WHERE ID = ##### statement from the have or want table
Furthermore i would need to make comparisons of user to user item lists, most common items, user with most items, complete user searches for items that one user wants and the other user has... - blah blah
The amount of users will range from 5000 - 20000
and each user averages about 15 - 20 items
will this be a viable MySQL structure or do i have to rethink my strategy?
Thanks alot for your help!
This will certainly be a viable structure in mysql. It can handle very large amounts of data. When you build it though, make sure that you put proper indexes on the user/item IDs so that the queries will return nice and quick.
This is called a one to many relationship in database terms.
Table1 holds:
userName | ID
Table2 holds:
userID | ItemID
You simply put as many rows into the second table as you want.
In your case, I would probably structure the tables as this:
users
id | userName | otherFieldsAsNeeded
items
userID | itemID | needWantID
This way, you can either have a simple lookup for needWantID - for example 1 for Need, 2 for Want. But later down the track, you can add 3 for wishlist for example.
Edit: just make sure that you aren't storing your item information in table items just store the user relationship to the item. Have all the item information in a table (itemDetails for example) which holds your descriptions, prices and whatever else you want.
I would recommend 2 tables, a Wants table and a Have table. Each table would have a user_id and product_id. I think this is the most normalized and gives you "unlimited" items per user.
Or, you could have one table with a user_id, product_id, and type ('WANT' or 'HAVE'). I would probably go with option 1.
As you mentioned in your question, yes, it would make much more sense to have a separate tables for WANTs and HAVEs. These tables could have an Id column which would relate the row to the user, and a column that actually dictates what the WANT or HAVE item is. This method would allow for much more room to expand.
It should be noted that if you have a lot of of these rows, you may need to increase the capacity of your server in order to maintain quick queries. If you have millions of rows, they will have a great deal of strain on the server (depending on your setup).
What you're theorizing is a very legitimate database structure. For a many to many relationship (which is what you want), the only way I've seen this done is to, like you say, have a relationships table with user_id and item_it as the columns. You could expand on it, but that's the basic idea.
This design is much more flexible and allows for the infinite items per user that you want.
In order to handle wants and have, you could create two tables or you could just use one and have a third column which would hold just one byte, indicating whether the user/item match is a want or a need. Depending on the specifics of your projects, either would be a viable option.
So, what you would end up with is at least the following tables:
Table: users
Cols:
user_id
any other user info
Table: relationships
Cols:
user_id
item_id
type (1 byte/boolean)
Table: items
Cols:
item_id
any other item info
Hope that helps!
Im going to develop Stock maintaining system using php+mysql. which will runs on server machine, so many users can update stock data. (in/out)
Im currently working on this system. I have following problems.
User A opens record “A”. ex- val=10
User B opens record “A”. ex - val=10
User A saves changes to record “A”. ex - val=10+2=12 (add 3 items, then stock should be 12)
User B saves changes to record “A”. ex - here i need to get record "A" value AS = 12, then B update val=12+3=15. (then add 3 items final stock will be 15)
In this example, User A’s changes are lost – replaced by User B’s changes.
I know mysql Innodb facilitate row level locking. My question is ,
is innodb engine do concurrent control ; and is this enough to (Innodb) to avoid "lost update" problem. or need to do extra coding to avoid this problem.
Is this enough please tell me how innodb works with my previous example. (lost update)
(sorry for my bad english)
thanks
InnoDB allows concurrent access, so User A and User B could definitely be handling the same data. User A will update the row based on his/her data, then User B can do the same -- ultimately resulting in User A's loss of data.
You should consider an alternative, if every update is vital to keep. For example, if both users are updating a blog article, you could make a new table that holds all these edits. Both user's edits would be preserved, despite when they retrieved the article content. When the article is retrieved, you can check when the most recent edit occurred and retrieve that instead.
Look, there's something called "versioning".
The idea is simple:
When a user opens a record, he also gets the version number.
When he saves changes to that record, at the sql level, the update is conditional, meaning that the update will happen ONLY if the current version is the same. This update also increases the version by one.
This way ensures you're not writing to a "stale" copy of your record.
Hope it's clear.
You could also implement some polling to the server, keep a record of the last update of the row and if it changes where if user B updates the record before A then you can notify user A that the record has been updated and that his changes wont take effect or you could update the values dynamically.
You can use two tables for this purpose. First - StockItems with item name, id, and count. Second - StockActivities with item id and operation amount.
To add or remove items from stock you need to insert records to the second table StockActivities, with item id and quantity that is added / removed.
item id:1, qnt: +10
item id:1, qnt: +1
item id:10, qnt: -2
Field count of StockItems table should be "read only" for users and should be calculated based on StockActivities table.
For example, you can create after insert trigger for StockActivities table that will update count field of added / removed stock item.
Judging by comments left, I think it prudent to respond with some pointers I have come across, in case someone needs to.
If you only want to update a value by an offset, you can do this quite easily and atomically. Assume the following data:
+----+--------+-------+
| id | name | price |
+----+--------+-------+
| 1 | Foo | 49 |
| 2 | Bar | 532 |
| 3 | Foobar | 24 |
+----+--------+-------+
We can now run the following queries to add one to the price:
select id, price from prices where name like "Foo";
// Later in the application
update prices set price=50 where id=1;
This is the non-concurrent/non-atomic way to do this, assuming that there is no changes or fetches in between the two queries. A more atomic way to do this, is the following.
select id, price from prices where name like "Foo";
// Later in the application
update prices set price=price+1 where id=1;
Here, this query allows us to increment the price in one query, eliminating the ability for others to come and update between two queries.
Additionally, there are methods of updating data safely, where the nature of the update is not a simple addition or subtraction. Let's say, here, that we have the following data:
+----+----------+---------------------+
| id | job_name | last_run |
+----+----------+---------------------+
| 1 | foo_job | 2016-07-13 00:00:00 |
| 2 | bar_job | 2016-07-14 00:00:00 |
+----+----------+---------------------+
In this case, we have multiple different clients, where all clients can do any job. We then need a way to dispatch work to one client, and only one client.
We can either use a transaction, where we will error out if the record has been updated or we can use a technique called CAS, or Compare and Swap.
Here's how we do this in MySQL:
update jobs set last_run=NOW() where id=1 and last_run='2016-07-13 00:00:00'
Then, in the data returned from mysql, we can tell the number of rows affected. If we have affected a row, then we have successfully updated it, and the job is ours. If there were no rows updated, then another machine has updated it, claiming the job there.
This works because any update from our application will cause the column to change, and since the column's value is a condition for completing the updated, it will avoid concurrent changes, allowing the application to decide what occurs next.
This is a followup to a question I posted a few days ago.
basically, I have a site with six links. In order to access the site, users must log in using LDAP authentication. When they do this, I grab some of their account credentials (username, firstname, lastname), and store it in a PHP $_SESSION variable.
That works; the user can log in, and the session data is being stored successfully.
Now, I want to set up a way to track which links have been clicked by what users. Basically just store a time stamp in the database of when they clicked the link. I want to be able to see who has (or has not) clicked each link, and when.
Can I do this in a single table / would that be a bad idea? I was thinking setting up the table like this:
TABLE (each bullet indicative of a column)
auto-incrementing ID
user account name: abc1234
user account first name: John
link 1: Last Accessed 5/2/2012 at 4:15PM
link 2: NULL
link 3: NULL
link 4: Last Accessed 5/1/2012 at 2:20PM
link 5: NULL
link 6: NULL
basically the above would say that "John" had only clicked the first and 4th links. The rest are null because he has never accessed them. If he were to click #1 again, it would overwrite with the more recent date/time.
Can I do this in a single table? or will that create complications? I feel like the thing I will have the hardest time with is checking to see if the user is already in the database before adding the info (ie so that if John logs in a second time, a whole new row isn't created for him)
Thanks for any help!
That would be a bad idea. What if you wanted to have a seventh link? What if the user format would change?
This solution requires 3 tables:
Users - contains user data (And a user ID).
Links - contains link data (And a link ID).
Clicks - many-to-many relationship between users and links.
That third table would look like this:
user_id | link_id | timestamp
-----------------------------
1 | 2 | ...
2 | 2 | ...
1 | 3 | ...
............
why not just have
increment_ID
Account_ID
Link_URL
Timestamp
Then just insert a new record for each click. You also don't need to manage links since you'll store the entire URL path