CODEWITHSUNDEEP
mongodbdatabase-designdatabase
Mia
Mia

Reputation: 6531

Database and item orders (general)

I'm right now experimenting with a nodejs based experimental app, where I will be putting in a list of books and it will be posted on a forum automatically every x minutes.

Now my question is about order of these things posted.

I use mongodb (not sure if this changes the question or not) and I just add a new entry for every item to be posted. Normally, things are posted in the exact order I add them.

However, for the web interface of this experimental thing, I made a re-ordering interaction where I can simply drag and drop elements to reorder them.

My question is: how can I reflect this change to the database?

Or more in general terms, how can I order stuff in general, in databases?

For instance if I drag the 1000th item to 1st order, everything below needs to be edited (in db) between 1 and 1000 the entries. This does not seem like a valid and proper solution to me.

Any enlightenment is appreciated.

Upvotes: 1

Views: 57

Answers (1)

TAM
TAM

Reputation: 1741

An elegant way might be lexicographic sorting. Introduce a String attribute for each item. Make the initial length of the values large enough to accomodate the estimated number of items. E.g., if you expect 1000 items, let the keys be baa, bab, bac, ... bba, bbb, bbc, ...

Then, when an item is moved from where it is to another place between two items, assign a value to the sorting attribute of the moved item that is somewhere equidistant (lexicographically) to those items. So to move an item between dei and dej, give it the value deim. To move an item between fadd and fado, give it the value fadi.

Keys starting with a were initially not used to leave space for elements that get dragged before the first one. Never use the key a, as it will be impossible to move an element before this one.

Of course, the characters used may vary according to the sort order provided by the database.

This solution should work fine as long as elements are not reordered extremely frequently. In a worst case scenario, this may lead to longer and longer attribute values. But if the movements are somewhat equally distributed, the length of values should stay reasonable.

Upvotes: 1

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