Question

Below is my (simplified) schema (in MySQL ver. 5.0.51b) and my strategy for updating it. There has got to be a better way. Inserting a new item requires 4 trips to the database and editing/updating an item takes up to 7!

items: itemId, itemName
categories: catId, catName
map: mapId*, itemId, catId
* mapId (varchar) is concat of itemId + | + catId

1) If inserting: insert item. Get itemId via MySQL API.
Else updating: just update the item table. We already have the itemId.

2) Conditionally batch insert into categories.

INSERT IGNORE INTO categories (catName) VALUES ('each'), ('category'), ('name'); 

3) Select IDs from categories.

SELECT catId FROM categories WHERE catName = 'each' OR catName = 'category' OR catName = 'name'; 

4) Conditionally batch insert into map.

INSERT IGNORE INTO map (mapId, itemId, catId) VALUES ('1|1', 1, 1), ('1|2', 1, 2), ('1|3', 1, 3); 

If inserting: we’re done. Else updating: continue.

5) It’s possible that we no longer associate a category with this item that we did prior to the update. Delete old categories for this itemId.

DELETE FROM MAP WHERE itemId = 2 AND catID <> 2 AND catID <> 3 AND catID <> 5; 

6) If we have disassociated ourselves from a category, it’s possible that we left it orphaned. We do not want categories with no items. Therefore, if affected rows > 0, kill orphaned categories. I haven’t found a way to combine these in MySQL, so this is #6 & #7.

SELECT categories.catId FROM categories LEFT JOIN map USING (catId) GROUP BY categories.catId HAVING COUNT(map.catId) < 1; 

7) Delete IDs found in step 6.

DELETE FROM categories WHERE catId = 9   AND catId = 10; 

Please tell me there’s a better way that I’m not seeing.

Answer 1

Steps 6 & 7 can be combined easily enough:

DELETE categories.* FROM categories LEFT JOIN map USING (catId) WHERE map.catID IS NULL; 

Steps 3 & 4 can also be combined:

INSERT IGNORE INTO map (mapId, itemId, catId)     SELECT CONCAT('1|', c.catId), 1, c.catID     FROM categories AS c     WHERE c.catName IN('each','category','name'); 

Otherwise, your solution is pretty standard, unless you want to use triggers to maintain the map table.