如果找不到参考表中添加记录的最佳方法

Question

I'm trying to implement a simple tag system in my app. When users want to tag an object, they can use existing tags and/or create new tags at the same time. I have a table 'tag' which just stores the unique tag string value as a PK. In 'object_tag' I have a FK reference to this column. In a request from the client there can be multiple tags for one object. On the server I will loop through all the tags and store them in 'object_tag'. If the tag doesn't exist in the 'tag' table, it should be inserted first.

What is the most efficient way to do this? I could just check if the tag exists before each insert, but I want to minimize the database I/O.

Answer 1

You will need 3 tables as follows:

Object - list of objects, primary key oid Tag - list of tags, primary key tid ObjectTag - pairs of oid, tid values

See also:

Tags: Database schemas

The Problem: You want to have a database schema where you can tag a bookmark (or a blog post or whatever) with as many tags as you want. Later then, you want to run queries to constrain the bookmarks to a union or intersection of tags. You also want to exclude (say: minus) some tags from the search result.

• " MySQLicious " solution - uses one denormalized table. MySQLicious imports del.icio.us data into a table with this structure.
• "Scuttle" solution - Scuttle organizes its data in two tables. That table “scCategories” is the “tag”-table and has got a foreign key to the “bookmark”-table.
• "Toxi Solution" Toxi came up with a three-table structure. Via the table “tagmap” the bookmarks and the tags are n-to-m related. Each tag can be used together with different bookmarks and vice versa. This DB-schema is also used by wordpress .

see also Tagging system: Toxi solution questions