检查用户是否投票的正确方法是什么？

Question

For example, 10 results are displayed from MySQL table products and each product has a like and dislike button. If the user presses like or dislike, the voted table is updated.

Now what i'm having trouble with is: What is the right way of checking if the user has voted or not? What to store If product has been voted with like or dislike?

If there is 300 results, I don't want to do 300 queries to check in the voted table if the productid and userid is present. What would be the correct way of doing this? I still want to show the results, just not the like or dislike button if the user has voted.

Answer 1

Table A stores products, eg

id | product |

Table B stores user votes, eg

id | user_id | product_id | vote (like/dislike)

Then you can do a simple join query

SELECT `A`.`id`, `A`.`product`, `B`.`vote` from `A` LEFT JOIN `B` on `A`.`id` = `B`.`product_id` WHERE `B`.`user_id` = $current_user_id_value;

Then the result set will look like this

id |   product   |   vote   |
 1 | "product 1" |  NULL    |
 2 | "product 2" |  like    |
 3 | "product 3" |  dislike |
 4 | "product 4" |  NULL    |
...

Answer 2

使用左外部联接添加投票表中的行，其中用户ID与当前用户匹配，产品ID与产品表中的产品ID匹配到结果集。

Answer 3

The easiest is setting a cookie for the user and the products they have voted. Of course, the user could just delete their cookies and vote again.

The consistent way would be the one you describe, saving a row for each productId and userId . No need to query multiple times, though, you'd just have to do SELECT count(productID) WHERE productId=1 and userId=42

You can choose, amongst different scenarios, between consistency or performance. Maybe another database engine would be the best choice, together with cookies.

Answer 4

I have an odd solution :)

1. Create a field in your product table with name votes , type blob (or text)

2. Save the voted user in an array like:

   $votes = array( 1 => true, // userId => like/dislike (true/false) );

3. Use serialize & unserialize with object $votes (field vote ) to load or save voted users to you database. With less than 1 thounsand users votes on a product, the votes field is as small as acceptable I guess :)

4. Then you can check if the user is voted by isset($votes[$userId]) and like or dislike by:

   if (isset($votes[$userId])) if ($votes[$userId] == true) echo 'like'; else echo 'dislike';

Because you do the checking by PHP so execute time doesn't matter.

Hope this helps!

Answer 5

you can use memcache, to have the values stored with you as key=>value pair,

key can be "product_id+user_id" and when ever any change happens, update the db as well as memcache.